Paludicola vol 8, issue 2 March 2011

PALUDICOLA SCIENTIFIC CONTRIBUTIONS of the ROCHESTER INSTITUTE OF VERTEBRATE PALEONTOLOGY

VOLUME 8 NUMBER 2

11 APRIL 2011 ISSN 1091-0263

PALUDICOLA SCIENTIFIC CONTRIBUTIONS OF THE ROCHESTER INSTITUTE OF VERTEBRATE PALEONTOLOGY Editors William W. Korth Rochester Institute of Vertebrate Paleontology 265 Carling Road Rochester, NY 14610 Phone (585) 482-0203 e-mail: [email protected] Judy A. Massare Department of Earth Sciences State University of New York, College at Brockport Brockport, NY 14420 Phone (585) 395-2419: Fax (585) 395-2416 e-mail: [email protected]

EDITORIAL POLICY Paludicola is published under the auspices of the Rochester Institute of Vertebrate Paleontology (RIVP). It is intended to serve as an “in-house” publication for students and professional paleontologists who are not affiliated with institutions that provide such a publication. All manuscripts considered for publication in Paludicola are expected to be original and have not been published elsewhere in any other form or are not being considered for publication anywhere else. This journal is intended as an outlet for papers on any aspect of Vertebrate Paleontology. Paludicola is published twice annually (Fall and Spring). All submitted manuscripts are subject to review by external qualified specialists and the editorial staff of Paludicola. The format of all submitted manuscripts should follow that of the Journal of Vertebrate Paleontology (printed in the first issue of each year). Questions about other editorial policies will be addressed by the editorial staff upon request. Please contact the editorial staff for prices of subscriptions and back issues (prices are subject to change). Back issues of volumes 1 – 6 can be purchased from PaleoPublications Inc. Prices and listings are available on-line at www.paleopubs.com.

Copyright  2011 by the Rochester Institute of Vertebrate Paleontology

Paludicola 8(2):75-90 March 2011 © by the Rochester Institute of Vertebrate Paleontology

RODENTS FROM THE CHADRONIAN (LATEST EOCENE) MEDICINE POLE HILLS LOCAL FAUNA, NORTH DAKOTA. PART 1. EUTYPOMYIDAE, CYLINDRODONTIDAE AND PIPESTONEOMYS Allen J. Kihm Department of Geosciences, Minot State University, 500 University Ave W, Minot, ND 58707

ABSTRACT The Medicine Pole Hills local fauna is a large Chadronian fauna composed of more than 4600 mammal specimens, mostly isolated teeth, derived from a limited sequence of mudball conglomerates and sandstones. The producing layer probably represents an early stage of deposition of the Chadron Formation in North Dakota, but it may not be related to any of the named members of the formation. The material described includes Eutypomys parvus, Cylindrodon collinus, Pseudocylindrodon neglectus, Ardynomys saskatchewensis and Pipestoneomys sp. The samples of E. parvus and A. saskatchewensis include teeth not previously described for these taxa. The assemblage has the greatest commonality to the middle Chadronian Calf Creek local fauna of southern Saskatchewan. This similarity does not necessarily indicate a middle Chadronian age for the Medicine Pole Hills local fauna. The lack of late early Chadronian localities with large samples of rodents may exaggerate the apparent differences between these faunas and the Medicine Pole Hills sample. The Calf Creek and Medicine Pole Hills local faunas may represent an intermediate stage between the McCarty’s Mountain and Pipestone Springs faunas of Montana. The Medicine Pole Hills fauna may be somewhat older than the Calf Creek local fauna based on the occurrence of Leptomeryx yoderi.

(Murphy et al., 1993), but continuing studies of the geology, particularly the heavy minerals, suggest this correlation is poorly supported (Webster and Kihm, 2009). The unit producing the fossils probably belongs within the Chadron Formation, but its correlation to, or stratigraphic relationship with the Chalky Buttes Member is yet to be determined. The specimens described in this study were collected by dry and wet screening over a number of years. The initial sample was collected between 1989 and 1993 by personnel of the PTRM through surface collecting and dry screening an undetermined amount of matrix from the most surficial units. This collection includes approximately 1500 mammal specimens. Stratigraphically controlled samples were taken in 2004 from a trench cut down to the base of the unit. Seven samples totaled 3.1 tonnes of matrix and produced approximately 1100 mammal specimens. The specimens recovered from each of the sampled intervals were compared and no faunal distinction was noted between the lowest and highest units, although the samples did vary in abundance of fossils. As there was no evidence of a faunal distinction between the sampled intervals, a portion of the spoil pile associated with digging the trench was processed in 2006. From the 4.4 tonnes processed, approximately 2000 mammal specimens were recovered.

INTRODUCTION This is the third in a series of papers that describe the mammals of the Medicine Pole Hills local fauna of southwestern North Dakota. Previous papers have dealt with the multituberculates (Schumaker and Kihm, 2006) and soricids (Kihm and Schumaker, 2008). In relationship to the rest of the fauna, rodents comprise about 60% of the more than 4600 mammal specimens, most of which are isolated teeth. The most common rodents are the eomyids, totaling more than 2300 specimens and about 50% of the total mammal specimens. The three rodent groups described in this study represent about 4% of the total mammal specimens. Background—The Medicine Pole Hills local fauna specimens in this study come from a single quarry, Pioneer Trails Regional Museum (PTRM) Locality V89002, in Bowman County, North Dakota. The quarry sample was taken from a series of mudball conglomerate and sandstone units (see Schumaker and Kihm 2006, for details) totaling approximately 5.5m in total thickness. These lie unconformably on the late Paleocene Tongue River Formation and are not overlain by any other geologic unit in any of the known exposures. The beds have been correlated with the Chalky Buttes Member of the Chadron Formation 75

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At a minimum, 7.5 tonnes of fossiliferous matrix were processed using 0.84mm screens. More than 50% of the more than 4600 mammal specimens were recovered from the smallest screened interval (0.84-1.4 mm). The only collections of Chadronian material of comparable magnitude are the Raben Ranch local fauna (Ostrander, 1980) with 4462 specimens, the Calf Creek local fauna with approximately 7000 specimens (J. Storer, pers. comm. 2005), the Flagstaff Rim sequence of faunas with very approximately 10,000 specimens (R. Emry, pers. comm. 2008) and the Pipestone Springs local fauna which is represented by several hundreds of specimens in each of several major museums (Carnegie Museum of Natural History, US National Museum, American Museum of Natural History, Field Museum of Natural History, among others). ____________________________________________ TABLE 1. Abbreviations used in this paper

Museums PTRM CM

Pioneer Trails Regional Museum, Bowman, North Dakota Carnegie Museum of Natural History, Pittsburgh, Pennsylvania

CMN

Canadian Museum of Nature, Ottawa, Ontario

RSM

Royal Saskatchewan Museum, Regina, Saskatchewan

ROM

Royal Ontario Museum, Toronto, Ontario

Measurements n

number of specimens

OR

observed range

AP

Anteroposterior length

W

Width, maximum

Wa

Width anterior

Wp

Width posterior

Teeth (subscript = lower tooth, superscript = upper tooth) P

Premolar

D

Deciduous

M

Molar

R, L

Right, Left

___________________________________________ Abbreviations used are given in Table 1. All measurements are given in millimeters unless otherwise indicated. The classification of rodents follows Korth (1994) and tooth nomenclature is based on Wood and Wilson (1936).

SYSTEMATIC PALEONTOLOGY Family Eutypomyidae Miller and Gidley 1918 Genus Eutypomys Matthew 1905 Eutypomys parvus Lambe 1908 (Figure 1, Table 2) Referred Specimens—all PTRM: RDP4 8338; LDP4 1398, 4866, 6100, 7924, 10967; RP4 10417, 10973; LP4 4900, 10997; RM1 or 2 1364, 1955, 7290, 7715, 8323, 10966, 10971, 10980, 10986, 10989, 10991, 10992, 10993; LM1 or 2 1327, 2098, 7292, 8006, 10985; RM3 10969, 10987; LM3 6275, 7935, 10968, 10979, 10990; RDP4 7425, 7949, 10982, 10983, 10994, 16012; LDP4 11013; RP4 5028, 10965; LP4 6150, 10972, 10975, 10996; RM1 or 2 1488, 2629, 5022, 5029, 5105, 6158, 6206, 7291, 7943, 10970, 10976, 10978, 10981, 10988, 11019; LM1 or 2 2012, 6126, 7397, 7712, 8319, 10995, 11004; RM3 1397, 5095, 10977; LM3 5027, 5032. Description—The DP4 (Fig. 1F) is similar to the 4 P (Fig. 1G) with three notable differences. The DP4 is smaller than the P4, the anterocone is more widely separated from the protoloph expanding the anterobuccal portion of the tooth, and the protocone/hypocone are more widely separated from the paracone/metacone. As noted by Storer (1978), the P4 of E. parvus is similar to that of E. thomsoni, but the tooth does show distinctions. The anterior cingulum is connected to the protoloph at about the midline of the tooth and continues as a strong loph to the anterobuccal corner of the tooth, often ending in a large oval anterocone which is not connected to the paracone. This creates an expanded anterobuccal corner for the tooth, a feature which can be seen on ROM 6314, a specimen figured by Russell (1972, Figure 9I) which he identified as a RM1or 2, but which is actually a left P4. This is in contrast to the condition described by Wood (1937) for E. thomsoni where the anterior cingulum connects to the protoloph near the paracone and extends both lingually towards the protocone and buccally to the anterobuccal corner of the tooth. However, it is not known how consistent this connection is in specimens of E. thomsoni. The protoloph and metaloph are complete in all specimens. The mure is typically diagonal with the connection to the protocone on the buccal or posterobuccal corner of the cusp. From there, the mure trends buccally then bends posterolingually to the hypocone. In some specimens, there are constrictions on the mure and in PTRM 8338 (a DP4) the mure does not connect to the protocone. The mesoloph is variable, typically reaching the buccal margin of the tooth, but the mesoloph may also be paired (PTRM 10973). The posterior cingulum descends from the hypocone and ends near the posterior face of the

KIHM—CHADRONIAN RODENTS FROM NORTH DAKOTA

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FIGURE 1. Eutypomys parvus from the Medicine Pole Hills local fauna. A, PTRM 16012 RDP4; B, PTRM 5028 RP4; C, PTRM 10978 RM1 or 2; D, PTRM 7291 RM1 or 2; E, PTRM 1397 RM3; F, PTRM 4866 LDP4; G, PTRM 10417 RP4; H, PTRM 10985 LM1 or 2; I, PTRM 10990 LM3. Buccal is up and the bar scale represents approximately 1 mm. ___________________________________________________________________________________________________________________

metacone, but does not attach to that cusp, leaving at least a portion of the posterior valley open buccally. The posterior cingulum is close to the metaloph as in E. thomsoni. The mesostyle is variable, distinct in some specimens, not developed in others. The number and positions of accessory lophules from the protoloph, metaloph, mesoloph, anterior and posterior cingula are variable. The M1 and M2 specimens are generally similar to the P4 except that the anterior cingulum attaches more lingually, either to the protocone or to the protoloph just buccal to the protocone (Fig. 1H), and the anterior cingulum parallels the protoloph, but does not merge with it until very worn. None of the specimens show the development of a parastyle. The mure is typically complete forming a posterolingual loph to the hypocone, but in some specimens the connection to the protocone is either weak, or the mure attaches to the protoloph (PTRM 1327, 10991) which allows the lingual valley to extend towards center of the tooth. The metaloph is complete on all specimens and the posterior cingulum parallels the metaloph but does not attach to the metacone until a late stage of wear. The M3 of E. parvus (Fig. 1I) has not previously been described. The tallest cusp is the paracone. The

anterior cingulum is complete from the protocone to the paracone and unlike the more anterior teeth, it attaches to the paracone at the anterobuccal corner of the tooth. The protoloph is complete, the hypocone is variable, but typically is reduced. The posterior cingulum extends from the hypocone, or from the protocone if the hypocone is indistinct, to the buccal margin of the tooth. The metacone is very reduced. In PTRM 10969 it is a distinct cusp, in 6275 it is indistinct, but the mesostyle is enlarged and forms an elongate ridge, and in 10979, the mesostyle is either paired, or the more posterior cusp is the metacone (although it is not attached to the metaloph). The mesoloph is variable. The metaloph typically reaches the buccal margin of the tooth, but makes a weak connection in some specimens (PTRM 6275, 7425) to the posterior cingulum. In the lower dentition, smaller premolar specimens are interpreted as DP4, the larger as P4. RSM P1585.491 described by Storer (1978) as a P4 is likely a DP4 based on its small size and diverging roots. The permanent P4 specimens in the Medicine Pole Hills collection have parallel roots. The protoconid and metaconid of the DP4 are reduced (Fig. 1A), in some specimens they are separated at the apices and a small

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trigonid basin is present (PTRM 10983, 10994, 16012), in others the cusps are separated only by a minor groove. The ectolophid is complete in all specimens. The mesoconid is variable, in PTRM 16012 it is a distinct cusp with a buccad extension. In other specimens the mesoconid is less distinct and the buccad extension is absent. The mesolophid is variable, bifurcating or trifurcating with accessory ridges to the metalophulid II, lingual margin or hypolophid. The hypolophid is complete on all specimens as is the posterior cingulum. On some specimens the posterior cingulum is attached to the hypocone, in others it attaches to the hypolophid near the midline of the tooth. The metastylid is typically developed and nearly closes the talonid basin lingually. ____________________________________________ TABLE 2. Measurements of Eutypomys parvus teeth. Tooth Position DP4

P4

M1 or 2 M3

AP Wa Wp AP Wa Wp AP Wa Wp AP Wa

n

Mean

OR

5 6 6 4 4 4 18 17 15 7 7

2.50 2.26 2.30 2.64 2.66 2.56 2.63 2.98 2.90 2.20 2.31

2.39-2.68 2.13-2.42 2.20-2.49 2.39-2.84 2.58-2.84 2.42-2.67 2.31-3.06 2.67-3.45 2.67-3.33 2.00-2.52 2.23-2.47

AP 7 2.15 2.10-2.26 Wa 7 1.44 1.32-1.58 Wp 7 1.74 1.58-1.84 AP 5 2.71 2.62-2.81 P4 Wa 5 1.78 1.65-1.91 Wp 6 2.40 2.23-2.55 AP 18 2.56 2.29-2.88 M1or 2 Wa 17 2.57 2.13-2.88 Wp 18 2.60 2.23-2.94 AP 5 2.71 2.52-2.88 M3 Wa 5 2.45 2.33-2.65 Wp 5 2.08 1.91-2.26 _______________________________________________________ DP4

The P4 is similar to the DP4, but significantly larger (Fig. 1B). The only noted differences are that the metaconid and paraconid are taller than the talonid portion of the tooth and the mesoconid is more typically developed and it often has a buccad extension. The M1 and M2 (Figs. 1C,D) show the same level of variability as the DP4 and P4. The metaconid is the tallest cusp, with the entoconid a bit shorter. The protoconid is not connected to the metaconid by any loph until very late stages of wear, and this connection occurs initially at the lingual or buccal margins of the tooth. A valley extends from the anterobuccal corner of the tooth obliquely across the tooth to the

metastylid. The protoconid is connected to the metastylid by a ridge (metalophulid II) on most specimens. On a few specimens (such as PTRM 7291), this ridge connects to the posterior face of the metaconid and on a few specimens it connects to the mesolophid. The ectolophid is complete in all specimens except PTRM 5022 on which a narrow fissure occurs near the midpoint. On all other specimens, the buccal valley does not extend into the talonid basin. The hypolophid and posterior cingulum are complete in all specimens. The M3 is similar to the anterior molars (Fig 1E), the only noted difference is that the ectolophid is incomplete in two of five specimens, although the gaps in the ectoloph are narrow. In PTRM 5027, the mesoconid is separated by narrow notches both anteriorly and posteriorly. In PTRM 10977, the hypolophid does not reach the entoconid. Discussion—The collection from the Medicine Pole Hills represents the largest sample of teeth of E. parvus. The species was described by Lambe (1908) based upon a single P4 from the Chadronian of the Cypress Hills Formation. Russell (1972) described five additional specimens and Storer (1978) added six more, all isolated teeth, from the same formation. The Medicine Pole Hills sample includes 75 isolated teeth, including several tooth positions that have not been previously represented. E. parvus is smaller than E. thomsoni (Matthew, 1905). Based upon measurements of E. thomsoni given by Wood (1937), comparable tooth dimensions are 19%-50% larger than E. parvus specimens from the Medicine Pole Hills. The upper dentitions of these two species are generally similar in morphology. In the lower molars the primary difference is seen in the connection between the metalophulid I and the metalophulid II. In E. thomsoni, the metalophulid I connects to the ectolophid, metalophulid II, or mesolophid by a cross loph near the midline of the tooth and the valley beginning at the anterobuccal corner of the tooth does not reach across the tooth to the lingual border of the tooth. In E. parvus, there is no connection between the metalophulid I and the metalophulid II until very late stages of wear. The protoconid is typically connected to the metastylid, so the valley extends across the entire tooth (or to the internal margin if the metastylid is enlarged). Eutypomys inexpectatus (Wood, 1974) is larger than E. parvus, being comparable in size to E. thomsoni. The lower dentition is similar to E. parvus in having a valley separating the protoconid and metalophulid II from the metaconid and melatlophulid I, but this valley opens on the lingual face of the lower molars rather than on the anterolingual corner as in E. parvus. In addition, the basin between the anterior

KIHM—CHADRONIAN RODENTS FROM NORTH DAKOTA

cingulum and the metalophulid I opens posteriorly, a condition not seen in E. parvus. E. parvus differs from E. obliquidens (Storer, 1988) in having somewhat larger molars (2%-17%). In E. obliquidens, both the valley between the protoconid and metalophulid I and the valley between the protoconid and hypoconid extend across the entire tooth to the lingual margin. In E. parvus, the buccal valley between the protoconid and hypoconid ends at the ectolophid, which is almost always connected to the hypocone. If there is a gap in the ectolophid, it is narrow, unlike the wide valley seen in E. obliquidens. E. parvus appears to be intermediate between E. obliquidens and E. thomsoni in several features. E. parvus is intermediate in size between these species. E. obliquidens has both the anterior and posterior lingual valleys extend across the lower molars, E. parvus has only the anterior valley and E. thomsoni has neither of the valleys extend across the tooth. Finally, E. parvus is intermediate in age between the Duchesnean E. obliquidens and the Orellan E. thomsoni. The only record of E. thomsoni from the Chadronian is from Clark (1937) who reported two teeth which he compared to E. thomsoni, but which he later reported could not be found (Clark and Beerbower, 1967). Ostrander (1980) suggested that the eutypomyid material from the Raben Ranch local fauna represented a new species, which he did not name. The Raben Ranch sample included only two upper and two lower molars. The upper molar he described has features duplicated by several of the Medicine Pole Hills specimens, although perhaps not all on the same specimen. The mure connects the hypocone to the protoloph in PTRM 1327 and 10991 and the cross loph connecting the paracone to the metaloph is absent in some specimens (PTRM 10993), partial in others (PTRM 7292) and complete in others (PTRM 8006). The single M1 or 2 which Ostrander (1980) described has the characteristic separation of the protoconid from the metaconid by the oblique valley typical of E. parvus. The only feature which appears to distinguish the Raben Ranch species from E. parvus in the Medicine Pole Hills sample is the smaller size of the Raben Ranch teeth. Family Cylindrodontidae Miller and Gidley 1918 Genus Cylindrodon Douglass 1902 Cylindrodon collinus Russell 1972 (Figure 2, Tables 3-4a-e) Referred Specimens—all PTRM; RDP4 7722; LDP4 5915, 6229, 11002, 11012, 14606; LP4 8336, 10999; RM1 or 2 4988, 5023, 7455, 7719, 8324, 8335 (cf), 10299, 10398, 11006, 11027, 11028, 11030; LM1 or 2 2615, 5103, 5907, 7294, 7479, 7723, 8000, 8007,

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10952, 10998, 11009, 11011, 11015, 11032; RM3 11010, 11014; LM3 5017, 7391; LDP4 10301, 10936; RP4 7718, 7946; LP4 1399, 2047 (cf), 7710, 11005, 11025; RM1 or 2 7660, 10300, 11003, 11008, 11016, 11017, 11018; LM1 or 2 2587, 5021, 5024, 5098, 5911, 7711, 7923, 7934, 8320, 10935, 11000, 11029; RM3 5529, 5899, 7938; LM3 10962 (cf), 11031, 11033. Description—The DP4 (Fig. 2E) has not previously been described for C. collinus, but is similar to that of C. fontis figured by Black (1965). The protocone is more cuspate than on the molars. The anterior cingulum forms the anterior margin of the tooth and encloses the anterior basin. It attaches either to the protocone or to the protoloph. In one specimen (PTRM 11012, Fig. 2E) there is a lophule connecting the anterior cingulum and the protoloph dividing the anterior basin into two pits. The metaloph is complete except in PTRM 5915 where it essentially ends at the large metaconule. A metaconule is typically present, but unlike the condition seen in the upper molars, none of the specimens show a lophule connecting the metaconule with the posterior cingulum. The posterior cingulum is complete and attaches to the posterior face of the metacone, enclosing the posterior basin. The central basin is the deepest basin and rises to a broad buccal notch. Only PTRM 11012 has a mesostyle which is located on the posterior face of the paracone. The only P4 in the sample that preserves much of a crown pattern has a complete protoloph (Fig. 2G). There is a slight notch in the anterior cingulum and the shallow anterior basin opens anteriorly. The posterior basin is smaller, but deeper than the anterior basin. The central basin opens by a notch buccally. The specimen differs from the P4 of C. collinus figured by Russell (1972) in having the anterior cingulum with a notch, which is more similar to the P4 of C. fontis (Black 1965); however, in C. fontis, there is no protoloph. The upper molars are generally as described by Storer (1978) for the species, but the Medicine Pole Hills specimens show some additional variation (Fig. 2H-J). The protoloph is always complete to the paracone and about one quarter of the specimens show some development of a lophule from the protoloph to the anterior cingulum. In all specimens the anterior cingulum is complete to the buccal margin of the tooth and in most specimens ends at a parastyle. This cusp is variable when present, from a swelling on the anterior cingulum to a cusp as large as the paracone and separated from it by a distinct notch (PTRM 11032). The metaloph typically has a distinct metaconule, which may be a small swelling on the metaloph (PTRM 11006) or a large cusp (PTRM 7294). In PTRM 7455 (Fig 2I), the metaloph is not complete, but ends at the large metaconule. In all other specimens, the metaloph narrows lingual to the metaconule, but

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FIGURE 2. Cylindrodon collinus from the Medicine Pole Hills local fauna. A, PTRM 10301 LDP4; B, PTRM 7710 LP4; C, PTRM 7711 LM1 or 2; D, PTRM 5529 RM3; E, PTRM 11012 LDP4; F, PTRM 7722 RDP4; G, PTRM 10999 LP4; H, PTRM 10299 RM1 or 2; I, PTRM 7455 RM1 or 2; J, PTRM 8324 RM1 or 2; K, PTRM 7391 LM3. Buccal is up and the bar scale represents approximately 1 mm. ____________________________________________________________________________________________________________________

attaches to the protocone. In most specimens the metaconule gives rise to a lophule which attaches to the posterior cingulum. With wear, this divides the posterior basin into two pits. The posterior cingulum is complete to the posterior face of the metacone. The central basin is variably shaped; in some cases the protoloph and metaloph diverge buccally, in other specimens the lophs are nearly parallel. The central basin is deep and steep sided. It opens buccally by a notch which is variable in depth. In some specimens, a small mesocone is present. The M3 is similar to the description given by Storer (1978) although with some additional variability (Fig 2K). The metaloph is complete on all specimens,

but on PTRM 5017 it is a thin loph connecting low on the protocone. The metacone of this specimen is also oriented posterolingually, which creates a posterior basin that is elongate anteroposteriorly and which opens by a notch on the posterior face of the tooth, a condition similar to that described by Black (1965) for C. fontis. In all other specimens, the posterior cingulum is complete, enclosing a circular posterior basin. The protoconid and metaconid of the DP4 are separated by a valley (Fig. 2A). The posterior face of the trigonid forms a long sloping surface into the talonid basin. PTRM 10301, the less worn specimen, has a complete hypolophid and the posterior basin is

KIHM—CHADRONIAN RODENTS FROM NORTH DAKOTA

enclosed, although the entoconid is separated by a notch from the posterior cingulum. The only additional feature of note is the development of a large, crescentric hypoconulid. The P4 (Fig. 2B) matches the description of C. collinus given by Storer (1978). The only additional variation noted is in PTRM 7946 which has no development of a metalophid. All other specimens have the trigonid basin closed posteriorly by this lophule. The M1 and M2 match the description of these teeth given by Storer (1978). On the only two unworn specimens (PTRM 5911 and 7711, Fig. 2C), the metalophulid II is transverse rather than trending anterolingually as in C. fontis. The M3 (Fig. 2D) does not have the reduced posterior half seen in C. fontis, instead the talonid is only slightly narrower than the trigonid on unworn specimens and the hypolophid is as long as, or longer than, the metalophulid II. ___________________________________________ TABLE 3. Measurements of Cylindrodon collinus teeth, combined data. Tooth Position DP

4

P4 1 or 2

M

M3

AP W AP W AP W AP W

n

Mean

OR

6 6 2 2 24 24 4 4

1.87 1.44 1.47 1.44 1.80 1.65 1.50 1.27

1.74-1.94 1.23-1.65 1.36-1.58 1.23-1.65 1.42-2.16 1.13-2.49 1.39-1.58 1.03-1.52

AP 2 2.00 2.00-2.00 Wa 2 1.15 1.03-1.26 Wp 2 1.52 1.45-1.58 AP 6 1.99 1.74-2.20 P4 Wa 6 1.28 1.13-1.49 Wp 6 1.80 1.58-2.00 AP 17 1.96 1.78-2.13 M1 or 2 Wa 17 1.77 1.42-2.00 Wp 16 2.05 1.49-2.20 AP 6 1.71 1.55-1.91 M3 Wa 4 1.57 1.42-1.68 Wp 6 1.43 1.32-1.52 _______________________________________________________ DP4

Discussion—As noted by Emry and Korth (1996) there is considerable overlap in the sizes of the species of Cylindrodon. The Medicine Pole Hills sample is assigned to C. collinus because of the variable presence of a lophule connecting the metaloph and posterior cingulum on the upper molars. This loph is present to some degree in 11 of 13 specimens in the Medicine Pole Hills sample, and in 17 of 22 specimens in the Calf Creek sample at the Royal Saskatchewan Museum. In both samples, approximately one-half of the specimens show a strong connecting loph, and in the remainder there is a low or weak lophule. This loph is absent in C. fontis and consistently present in C.

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natronensis, C. solarborus and C. nebraskensis (Emry and Korth 1996). The Medicine Pole Hills specimens are larger than C. natronensis, and similar in size to C. solarborus when compared by stage of wear (Tables 3, 4a-e). Ostrander (1980, 1983) identified three species of Cylindrodon in the Raben Ranch local fauna, C. fontis, C. collinus and C. galbreathi. The only feature he used to distinguish C. fontis from C. collinus in the Raben Ranch sample was the separation of the posterior basin of the upper dentition into two pits, but as noted by Emry and Korth (1996) this feature is variably present in C. collinus, and as such the bulk of the Raben Ranch sample is likely composed of C. collinus. Korth (1992) synonymized C. galbreathi with C. nebraskensis, so two species of Cylindrodon do occur in the Raben Ranch fauna. Genus Pseudocylindrodon Burke 1935 Pseudocylindrodon neglectus Burke 1935 (Figure 3, Table 5) Cylindrodon fontis Matthew, 1903, in part Pseudocylindrodon neglectus Burke, 1935 Pseudocylindrodon silvaticus Russell, 1954 Referred Specimens—all PTRM RDP4 8288, 14960, 14705; RP4 10934; LP4 7388, 7393, 10945, 10946; RM1 or 2 5000, 7390; LM1 or 2 5010, 8009, 11024; RM3 4999 (cf), 7927, 8333; LM3 11026, 14970; LDP4 5537; RP4 6123, 7297, 7395, 10947; RM1 or 2 7944, 10413; LM1 or 2 7427, 7716, 7925, 7931; RM3 5525, 8337; LM3 5096, 5871, 11022. Description—The DP4 is triangular in occlusal outline. The single unworn specimen (PTRM 14705, Fig 3F)) has an anterior cingulum on the buccal half of the tooth that encloses a semicircular basin. The protocone is large and is connected by complete protoloph and metaloph to the external cusps. The posterior cingulum is only on the buccal half of the tooth and encloses a very narrow posterior basin. The central basin opens buccally by a wide V-shaped notch. PTRM 8288 differs in having a large anterocone separated by a notch from the paracone and in having a mesostyle which projects buccally at the opening of the central valley. The P4 (Fig. 3G) matches the description given by Black (1965) for this species. The M1 or 2 (Fig. 3H) specimens differ slightly from the Pipestone Springs specimens. In one specimen the anterior valley is open buccally, but in the other specimens, the anterior valley is either closed by a parastyle, or by the anterior cingulum attaching directly to the anterior face of the paracone. The posterior valley is closed in all specimens and the metaconule is attached to the posterior cingulum by a short loph in some specimens.

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TABLE 4a. Measurements of Cylindrodon collinus teeth in wear stage I*. Tooth Position DP4 P4 M1 or 2 M3

DP4

P4

M1 or 2

M3

n

Mean

OR

AP W AP W AP W AP W

4 4 10 10 2 2

1.91 1.37

1.87-1.94 1.23-1.62

1.93 1.27 1.53 1.11

AP Wa Wp AP Wa Wp AP Wa Wp AP Wa Wp

1 1 1 2 2 2 2 2 2 1 1 1

2.00 1.03 1.45 1.92 1.28 1.81 1.89 1.44 1.66 1.91 1.68 1.52

TABLE 4c. Measurements of Cylindrodon collinus teeth in wear stage III. Tooth Position DP4 P4

1.71-2.16 1.13-1.52 1.49-1.58 1.03-1.20

M1 or 2 M3

DP4 1.91-1.94 1.26-1.29 1.78-1.84 1.78-2.00 1.42-1.45 1.49-1.84

P4

M1 or 2

M3

n AP W AP W AP W AP W

1 1 1 1 -

AP Wa Wp AP Wa Wp AP Wa Wp AP Wa Wp

3 3 3 -

Mean

OR

1.74 1.65

1.78 1.52

2.03 1.73 2.10

1.94-2.13 1.65-1.81 2.00-2.20

*Wear stage defined by Emry and Korth (1996)

TABLE 4b. Measurements of Cylindrodon collinus teeth in wear stage II. Tooth Position DP4 P4 M1 or 2 M3

DP4

P4

M1 or 2

M3

n

Mean

AP W AP W AP W AP W

1 1 1 1 3 3 2 2

1.87 1.49 1.36 1.23 1.84 1.49 1.47 1.42

AP Wa Wp AP Wa Wp AP Wa Wp AP Wa Wp

1 1 1 4 4 4 2 2 1 2 2 2

2.00 1.26 1.58 2.03 1.28 1.80 1.89 1.79 2.16 1.68 1.49 1.41

OR

TABLE 4d. Measurements of Cylindrodon collinus teeth in wear stage IV. Tooth Position DP4 P4

1.81-1.87 1.32-1.58 1.39-1.55 1.32-1.52

M1 or 2 M3

DP4 1.74-2.20 1.13-1.49 1.58-2.00 1.81-1.97 1.62-1,97 1.62-1.74 1.42-1.55 1.32-1.49

P4

M1 or 2

M3

n AP W AP W AP W AP W

1 1 4 4 -

AP Wa Wp AP Wa Wp AP Wa Wp AP Wa Wp

5 5 5 2 2

Mean

OR

1.58 1.65 1.80 1.97

1.71-1.94 1.84-2.16

1.98 1.81 2.06 1.73

1.87-2.10 1.62-1.94 1.97-2.16 1.71-1.74

1.42

1.36-1.49

KIHM—CHADRONIAN RODENTS FROM NORTH DAKOTA

TABLE 4e. Measurements of Cylindrodon collinus teeth in wear stage V. Tooth Position DP4 P4 M1 or 2 M3

n AP W AP W AP W AP W

6 6 -

Mean

OR

1.55 2.20

1.42-1.65 2.00-2.49

AP Wa Wp AP P4 Wa Wp AP 5 1.96 1.81-2.10 M1 or 2 Wa 5 1.89 1.78-2.00 Wp 5 2.14 2.03-2.20 AP 1 1.55 M3 Wa 1 1.62 Wp 1 1.44 _______________________________________________________ DP4

The M3 (Fig. 3I) specimens match the description given by Black (1965) for P. neglectus. The DP4 (Fig 3A) is very low crowned. There is a minute remnant of a trigonid basin, and the trigonid forms a long slope into the shallow talonid basin. The ectolophid is complete as is the posterior cingulum. There is no evidence of a hypolophid. The entoconid is separated from the posterior extension of the metaconid by a wide shallow notch. Only one of the P4 specimens preserves details of the crown (PTRM 10947, Fig. 3B). In addition to being more mesodont, worn specimens differ from those of Cylindrodon collinus in being as broad as they are long. The trigonid has two distinct cusps with the metaconid larger and taller than the protoconid. These cusps are separated by a narrow fissure. The posterior slope of the trigonid is relatively long and less steep than that of C. collinus. The ectolophid is complete as is the posterior cingulum which rises to a tall entoconid. A very short hypolophid is attached to the entoconid, but this loph does not extend even to the midline of the tooth. The talonid basin is wide and shallow and opens buccally by a narrow notch that is almost as deep as the floor of the talonid basin. There is a posterior extension on the metaconid but there is no distinct metastylid. Two of the lower molar specimens are relatively unworn. PTRM 7925 (Fig. 3D) is very similar to the description given by Black (1965) for P. neglectus. Of note is the metalophulid II which drops from the apex of the protoconid to attach low on the posterolingual

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face of the metaconid. A posterior extension of the metaconid attaches to the entoconid and completely encloses the central basin. The hypolophid is complete, but is very low and rises little above the floor of the posterior basin. The entoconid rises above the posterior cingulum and is separated from it by a shallow notch. The second unworn specimen, PTRM 7931, differs in several features (Figure 3C). The metalophulid II is complete, but has its low point in the middle rather than at the metaconid. The hypolophid is complete and although below the level of the posterior cingulum rises well above the floor of the posterior basin. The posterior cingulum has a notch at the hypoconid and another shallower notch at the entoconid. The central basin opens lingually by a deep notch that extends to about one-half the depth of the central valley. A swelling on the posterolingual corner of the metaconid may represent a metastylid. Because these specimens are isolated teeth, it is not known if the variation relates to tooth position or represents individual variation. The M3 is similar to the description given by Black (1965), with one specimen (PTRM 8337) having a complete hypolophid, one (PTRM 5096) having an incomplete hypolophid with lophules from both the entoconid and hypoconid, and two specimens (PTRM 5871, 11022, Fig. 3E) having only minor lophules extending a short distance from the entoconid. ___________________________________________ TABLE 5. Measurements of the Pseudocylindrodon neglectus teeth. Tooth Position DP4 P4 M1 or 2 M3

DP4

P4

M1 or 2

M3

n

Mean

OR

AP W AP W AP W AP W

3 3 4 4 5 5 4 4

1.53 1.88 1.44 2.10 1.63 2.11 1.47 1.68

1.45-1.68 1.78-2.03 1.39-1.49 1.84-2.29 1.55-1.74 1.97-2.26 1.39-1.65 1.49-1.81

AP Wa Wp AP Wa Wp AP Wa Wp AP Wa Wp

1 1 1 4 4 4 5 5 5 5 5 5

1.58 1.07 1.32 1.89 1.34 1.93 1.71 1.57 1.81 1.89 1.66 1.59

1.78-2.00 1.16-1.52 1.81-2.10 1.55-1.91 1.49-1.71 1.78-1.84 1.68-2.16 1.36-1.94 1.42-1.78

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FIGURE 3. Pseudocylindrodon neglectus from the Medicine Pole Hills local fauna. A, PTRM 5537 LDP4; B, PTRM PTRM 10947 RP4; C, PTRM 7931 LM1 or 2; D, PTRM 7925 LM1 or 2; E, PTRM 11022 LM3; F, PTRM 14705 RDP4; G, PTRM 10934 RP4; H, PTRM 11024 LM1or 2; I, PTRM 8333 RM3. Buccal is up and the bar scale represents approximately 1 mm. ______________________________________________________________________________________________________________________

Discussion—The Medicine Pole Hills specimens do not represent P. medius (Burke, 1938) that has a P4 which is longer than it is wide, and a well developed hypolophid. In addition, the P4-M2 have mesostyles, which are absent in P. medius (Black, 1965). The Medicine Pole Hills specimens are comparable to the specimens from both the Calf Creek local fauna (Storer, 1978) and from the Pipestone Springs local fauna (Black, 1965), but are consistently smaller than P. neglectus from the Raben Ranch local fauna (Ostrander, 1980). Pseudocylindrodon silvaticus from the Kishenehn Formation of British Columbia. was considered distinct because the hypolophid of the M3 was incomplete (Russell, 1954). This condition is seen in several of the Medicine Pole Hills specimens (PTRM 5871, 11022) and, as noted by Russell, P. silvaticus is the same size as P. neglectus. Wood (1980) considered P. silvaticus to be a junior synonym of P. neglectus, a determination supported here by the variation in the Medicine Pole Hills M3 specimens. Genus Ardynomys Matthew and Granger 1925 Ardynomys saskatchewensis (Lambe) 1908 (Figure 4A-G, Table 6)

Sciurus? saskatchewensis Lambe, 1908 Prosciurus saskatchewanensis Russell,1934 Prosciurus saskatchewensis Russell, 1972 Ardynomys saskatchewensis Storer, 1978 ?Prosciurus saskatchewaensis Wood, 1980 Ardynomys saskatchewaensis Emry and Korth, 1996 Referred Specimens—all PTRM RM1 or 2 7478, 7926; LM1 or 2 11023, 11052; RM3 8332; LM3 11001, 14968; RDP4 10932; RP4 7295, 7717, 7726; LM1 or 2 8322, 11007, 11021; LM3 7272, 11020. Description—The single unworn M1 or 2 (PTRM 11052, Fig. 4F) has a large protocone with a slight anterior expansion that extends anterolingual to the attachment of the anterior cingulum. The anterior cingulum is complete and attaches to the anterior face of the paracone, enclosing a narrow anterior basin. The protoloph is complete. The posterior cingulum begins as a robust extension from the posterior face of the protocone that then trends buccally to attach to the posterior face of the metacone. The posterior basin is enclosed anteriorly by the complete metaloph. The metaconule is distinct and expanded toward the posterior cingulum, which would result in two distinct

KIHM—CHADRONIAN RODENTS FROM NORTH DAKOTA

pits at a later stage of wear. The central basin is the deepest basin and rises buccally to a high notch. A weak mesocone is attached to the paracone. The M3 (Fig. 4G) is more circular in outline compared to the broadly rectangular anterior molars. The anterior cingulum, protoloph, metaloph and posterior cingulum are all complete and the buccal margin is completely enclosed. The mesocone is moderately to well developed. The metaconule is present on all specimens. The single specimen interpreted as a DP4 (Fig. 4A) is longer than wide, in contrast to the P4 which is as wide as it is long. It also has a lower crown and the enamel does not extend down the posterobuccal root as it does in the permanent tooth. The metaconid forms the tallest portion of the trigonid, but there is no groove separating it from the protoconid. If there was a trigonid basin, it has been eliminated by wear. The posterior face of the trigonid slopes gradually into the talonid basin. The ectolophid is complete as is the posterior cingulum. The entoconid is positioned somewhat anteriorly, and a weak hypolophid extends from the entoconid about halfway across the basin towards the hypoconid. The talonid basin opens by a relatively broad notch. A posterior extension on the metaconid may represent the metastylid. The P4 (Fig. 4B,C) is about as broad as it is long. The metaconid and protoconid are separate at their apices by a shallow groove. These cusps are connected by a very low metalophid which encloses a shallow trigonid basin. The ectolophid is complete as is the posterior cingulum. The entoconid is not placed as far forward as in the deciduous tooth and forms the posterolingual corner of the tooth. A low hypolophid connects the posterior cingulum and ectolophid and encloses a shallow basin on one specimen (PTRM 7726); other specimens show no evidence of a posterior basin either because of wear or because of the absence of a hypolophid. The talonid basin opens lingually by a V-shaped notch. The posterior face of the metaconid has an expansion, but not to the extent seen in the deciduous tooth. PTRM 11021 (Fig. 4E) is an unworn M1 or 2. The metaconid is the tallest cusp and is connected to the protoconid by a strong, transverse anterior cingulum. The protoconid is elongate anteroposteriorly and the metalophid is attached approximately halfway between the anterior and posterior margins of the tooth. The metalophid is as strong as the anterior cingulum, although somewhat lower, and attaches to the posterior expansion of the metaconid on the lingual margin of the tooth. The ectolophid is complete, with the apex of the hypoconid placed close to the buccal attachment of the metalophid. The hypolophid is complete and attaches to the hypoconid and the entoconid. The posterior cingulum is complete and bends anteriorly on

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the lingual margin of the tooth to attach to the entoconid. The anterior and posterior basins are totally enclosed and nearly equal in size. The central basin is deep, anteroposteriorly narrow and very steep sided. It opens by a narrow notch between the entoconid and the metalophid. PTRM 11007 (Fig. 4D) differs slightly, in that the metalophid attaches to the protoconid and the metaconid, enclosing a smaller, more shallow anterior basin. The central basin is wider and there is a distinct metastylid closing the lingual end of the basin. The M3 has a narrow trigonid basin enclosed by metalophid which attaches to the metaconid. The hypolophid is complete from the entoconid to the ectolophid. The posterior cingulum is complete and encloses a semicircular posterior basin. __________________________________________ TABLE 6. Measurements of Ardynyomys saskatchewensis teeth. Tooth Position M1 or 2 M3

AP W AP W

n

Mean

OR

3 3 2 2

1.98 2.75 2.28 2.26

1.84-2.20 2.49-3.18 2.10-2.45 2.20-2.33

AP 1 2.13 Wa 1 1.49 Wp 1 1.97 AP 3 2.23 2.20-2.26 P4 Wa 3 1.64 1.52-1.71 Wp 3 2.28 2.10-2.39 AP 3 2.27 2.10-2.36 M1 or 2 Wa 3 2.20 1.78-2.68 Wp 3 2.39 2.03-2.81 AP 2 2.50 2.36-2.65 M3 Wa 2 2.28 2.13-2.42 Wp 2 2.28 2.16-2.39 _______________________________________________________ DP4

Discussion—These specimens are assigned to A. saskatchewensis because of the connection of the metaloph and posterior cingulum seen on most of the upper molars. This connection is not seen in A. occidentalis (Emry and Korth, 1996). The upper molars all have the anterior and posterior cingulum fused to the buccal cusps, completely enclosing the anterior and posterior basins. The specimens are larger than named species of Pseudocylindrodon, except for P. texanus. Pseudocylindrodon texanus does not show an enlarged metaconule and there is no connection between the metaloph and the posterior cingulum (Wood, 1974). The rather convoluted taxonomic history of this species has been summarized by Emry and Korth (1996), but in short the species has previously been represented by only a single unworn tooth (the holotype, CMN 6479). The only additional specimens referred to this species are a very worn upper molar

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FIGURE 4. Ardnyomys saskatchewensis and Pipestoneomys from the Medicine Pole Hills local fauna. A-G, Ardnyomys saskatchewensis; A, PTRM 10932 RdP4; B, PTRM 7295 RP4; C, PTRM 7726 RP4; D, PTRM 11007 LM1 or 2; E, PTRM 11021 LM1 or 2; F, PTRM 11052 LM1 or 2; G, PTRM 14968 LM3. H-I Pipestoneomys sp.; H, PTRM 10974 RP4; I, PTRM 6167 LM1 or 2. Buccal is up and the bar scale represents approximately 1 mm. ____________________________________________________________________________________________________________________

(RSM P661.44) and an edentulous maxillary fragment (RSM P661.45). Assuming that the Medicine Pole Hills specimens are correctly assigned, they represent the most complete record of the dentition of A. saskatchewensis to date. The species named by Lambe (1908) clearly has priority over A. occidentalis (Burke 1936) as noted by Storer (1996). if the species are synonymous. Storer (1978) noted several features that distinguished the holotype of A. saskatchewensis, from the referred skull of A. occidentalis. Storer erroneously stated that CM 1055, the skull figured by Burke (1936, Fig. 1) was the holotype; the correct holotype is CM 1056, the lower jaw shown in the same figure. That being the case, the holotypes of A. saskatchewensis and A. occidentalis have no teeth in common. That point aside, the features noted by Storer (1978, p. 16) that distinguish A. saskatchewensis were a) "strong anterior and posterior cingula that close off valleys" b) "distinct metaconule", c) "metaloph very low near protocone" and d) "metaloph broader than protoloph". Emry and Korth (1996) added the connection of the metaloph to the posterior cingulum as another diagnostic feature of A. saskatchewensis. The Medicine Pole Hills specimens are approximately the same size as A.

occidentalis (Table 6) although the lower teeth tend to be narrower and the upper teeth tend to be wider than comparable teeth of that species. Finally, the Medicine Pole Hills M3 specimens all have the posterior and central valleys closed buccally, in contrast to the condition of A. occidentalis in which the central valley is open buccally, a feature noted by Burke (1936). Based on these differences, A. occidentalis appears to be distinct from A. saskatchewensis. Family incertae sedis Genus Pipestoneomys Donohoe 1956 Pipestoneomys sp. (Figure 4H-I) Referred Specimens—Both PTRM RP410974, LM 6167 Description—PTRM 10974 (Fig. 4H) is most probably a P4, although it may also represent a DP4. The amount of wear and the relative development of the roots suggest the former interpretation. There is a very large anterocone that is connected by the anterior cingulum to the protocone. The protocone is connected to the hypocone, in contrast to the P4 of P. pattersoni. The posterior cingulum is complete to the 1or 2

KIHM—CHADRONIAN RODENTS FROM NORTH DAKOTA

posterobuccal corner of the tooth. The metaloph is complete and the posterior basin is divided into two pits. There is no distinct metacone, but this may be due to the relatively advanced wear. The hypocone is connected to the paracone by an oblique loph which encloses a basin between the metaloph and the oblique loph. A lophule connects the oblique loph to the anterior cingulum. This encloses a basin between the protocone and hypocone. The ectoloph is complete from the metacone to the paracone but the paracone is separated by a deep groove from the anterocone. The anterior-posterior length is 2.71 mm, Wa is 2.03 mm and Wp is 1.81 mm. These measurements are greater than those of the P4 of P. pattersoni given by Alf (1962), but similar to the P4 measurements of P. pattersoni and P. bisulcatus given by Ostrander (1980). PTRM 6167 (Fig 4I) is an upper molar. The protocone is crescentric and gives rise to two lophs. The anterior cingulum forms the anterior border of the tooth. Just posterior and parallel to this is a second loph which encloses a transverse basin. These lophs join each other lingual to the paracone and are separated from the paracone by a shallow groove. There is no distinct parastyle. This differs from the holotype of P. bisulcatus in which the groove between the paracone and the buccal end of the anterior cingulum is deeper. There is a minor expansion on the more posterior loph towards the oblique loph from the hypocone. The hypocone is not connected to the protocone and the lingual valley extends across the tooth to the shallow groove at the anterobuccal corner of the tooth. An oblique loph connects the hypocone to the paracone and there is a very short lophule on the anterior side of the loph. The posterior cingulum is complete to the metacone. There are two minor lophules from the metacone extending into the posterior basin, but these to not reach the oblique loph. The metacone is connected to the paracone by a complete ectoloph which closes the posterior basin. The anterior-posterior length is 1.78 mm, Wa is 1.73 mm and Wp is 1.42 mm. Discussion—The P4 differs considerably from the only previously described P4 of Pipestoneomys (Alf, 1962). Some of these differences may be due to the more worn condition of the Medicine Pole Hills specimen, but some are probably due to individual variation. First, in P. pattersoni an oblique valley crosses the tooth, separating the protocone-anterocone from the hypocone. In PTRM 10974 this valley is closed lingually and medially by lophs. In P. pattersoni, the oblique loph does not reach the paracone (unlike the condition of the molars). In PTRM 10974, lophs from the hypocone reach both the metacone and the paracone. The characters that support an assignment to Pipestoneomys are the very large anterocone and protocone, and the anterior width

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being greater than posterior width. Ostrander (1980) reported P4 specimens of P. bisulcatus from the Raben Ranch local fauna but did not describe their morphology, the amount of variation of that tooth, or why these teeth were assigned to P. bisulcatus rather than P. pattersoni. The P4 of P. bisucatus, other than the specimens reported by Ostrander, is unknown and the species are similar in size. The single upper molar in the Medicine Pole Hills collection differs from the pattern of both P. bisulcatus and P. pattersoni in having two anterior lophs from the protocone to the anterobuccal corner of the tooth. The groove between the anterior lophs is very shallow, more similar to the pattern described for P. pattersoni (Donohoe, 1956), but in contrast to P. pattersoni, the posterior basin is not divided into two pits. The single posterior basin is more similar to the condition of P. bisulcatus. There appear to be several options on where to assign these specimens. The two anterior lophs from the protocone are unlike either P. bisulcatus or P. pattersoni, which could be used to justify, to some degree, assigning the specimen to a new species. The single posterior basin could support an assignment to P. bisulcatus as opposed to P. pattersoni. The shallow groove separating the anterior lophs from the paracone could support an assignment to P. pattersoni. Ostrander (1980), with a larger collection of Pipestoneomys specimens from the Raben Ranch local fauna, chose to assign some of those specimens to each of the named species, but provided no discussion on the range of variation. It seems equally likely, given the nature of the variation in taxa such as Eutypomys, that there may be considerable variation in the relative development and strength of lophs in Pipestoneomys. The fact that three different morphologies of similar sized upper molars, the only comparable teeth, occur at three different localities (Pipestone Springs, Sioux County, Nebraska and Medicine Pole Hills) could be indicative of distinct species, especially given the age differences between the faunas. However, at least two of these morphologic types occur in the Raben Ranch local fauna. Ostrander (1980) chose to interpret this as evidence of two contemporaneous species. Alternatively, it is not unreasonable to consider the identified differences between P. bisulcatus and P. pattersoni to be variants of a single species, with P. pattersoni being a junior synonym. The Medicine Pole Hills specimens suggest a higher degree of variation than previously described within Pipestoneomys, but the available sample does not allow for a determination of whether this variation is intraspecific. Pending a review of all of the Pipestoneomys material, no specific assignment is suggested for the Medicine Pole Hills specimens.

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CONCLUSIONS Eutypomys parvus has been reported from the Calf Creek local fauna (Storer 1978) and the Pipestone Springs local fauna (Tabrum et al., 1996). Both of these faunas are considered to be middle Chadronian by Prothero and Emry (2004), although they suggested that the Calf Creek local fauna is somewhat older than the Pipestone Springs local fauna (Prothero and Emry, 2004, Figure 5.2). Storer (1996) strongly suggested that the Calf Creek local fauna matched the late early Chadronian fauna from Flagstaff Rim, but reluctantly adopted a middle Chadronian interpretation. Eutypomys occurs in other Chadronian faunas, including E. inexpectatus from the earliest Chadronian Little Egypt local fauna of Texas (Wood, 1974) and E. cf. thomsoni from the late Chadronian Peanut Peak local fauna of South Dakota (Clark and Beerbower, 1967). Cylindrodon collinus has been reported from the Calf Creek local fauna (Storer, 1978) and the Raben Ranch local fauna (Ostrander, 1980), both of which are middle Chadronian. Cylindrodon natronensis (Emry and Korth, 1996) and C. fontis (Tabrum et al., 1996) have been reported from early to middle Chadronian faunas of Wyoming and Montana, respectively. Cylindrodon solarborus has been reported from the middle Chadronian of Wyoming, and C. nebraskensis has been reported from the middle to late Chadronian of Nebraska and Colorado (Emry and Korth, 1996). Pseudocylindrodon neglectus has been reported from the Duchesnean Porvenir, early Chadronian Little Egypt, and the late early Chadronian Airstrip local faunas of Texas (Wood, 1974), as well as the middle Chadronian Calf Creek (Storer, 1978), Raben Ranch (Ostrander, 1980), and Pipestone Springs (Black, 1965) local faunas. Pseudocylindrodon medius has been reported from the late early Chadronian McCarty’s Mountain local fauna and P. texanus has been reported from the Duchesnean Porvenir, late early Chadronian Little Egypt and late Chadronian Ash Springs local faunas of Texas (Wood, 1974). Ardynomys saskatchewensis has been reported only from the middle Chadronian Calf Creek local fauna (Storer, 1978). Ardynomys occidentalis has been reported from Duchesnean Diamond O and the late early Chadronian McCarty’s Mountain local faunas of Montana (Tabrum et al., 1996), the Duchesnean Porvenir, the earliest Chadronian Little Egypt and late early Chadronian Airstrip local faunas of Texas (Wood, 1974). Pipestoneomys has been reported from the middle Chadronian Pipestone Springs local fauna (Donohoe, 1956) and Chadron Formation of Nebraska (Alf, 1962; Ostrander, 1980), and the Orellan of Nebraska (West and Korth, 1994).

The most obvious interpretation from the rodent taxa considered in this report would be that the Medicine Pole Hills local fauna is middle Chadronian in age. All of the taxa, other than Pipestoneomys, occur in common with the Calf Creek local fauna. The Medicine Pole Hills fauna lacks any species (of the taxa considered in this report) restricted to early Chadronian or older faunas (e.g. Pseudocylindrodon medius, Ardynomys occidentalis). The only rodent taxon in the fauna of those considered here that occurs in the early Chadronian is P. neglectus, but this wide ranging species has been reported from the Duchesnean to the late Chadronian and from Texas to Saskatchewan. There does not appear to be a consistent biogeographic distribution for the taxa. Pseudocylindrodon neglectus occurs from Texas to Saskatchewan, Eutypomys parvus is known only from Montana, North Dakota and Saskatchewan. In contrast, the species of Cylindrodon seem to show restricted geographic distribution. Cylindrodon natronensis and C. solarborus occur in the late early and middle Chadronian of Wyoming (Emry and Korth, 1996), C. fontis occurs in late early and middle Chadronian of Montana (Tabrum et al., 1996), and C. collinus occurs in the middle Chadronian of Saskatchewan (Storer, 1978) and the Medicine Pole Hills local fauna. Ardynomys saskatchewensis is known only from Saskatchewan and North Dakota although the genus is widespread and was originally named based upon material from Asia (Matthew and Granger, 1925). Pipestoneomys has been reported from Nebraska, Montana, North Dakota, and perhaps from Saskatchewan (West and Korth, 1994). A middle Chadronian age interpretation would contradict the conclusion of Heaton and Emry (1996) who noted the occurrence of Leptomeryx yoderi in the Medicine Pole Hills fauna, a species that has been considered an index fossil for the late early Chadronian. However, the rodent data presented here cannot be taken as conclusive evidence for a middle Chadronian age. The late early Chadronian rodent fauna is not well known. The primary localities considered to represent the late early Chadronian are the Airstrip local fauna (TX), the Ahearn Member of the Chadron Formation (SD), the McCarty's Mountain local fauna (MT) and the Yoder and Flagstaff Rim (>15m below Ash B) faunas of Wyoming. Of these, the Airstrip local fauna has 5 rodent specimens representing 4 species (Wood, 1974), the Ahearn Member fauna given by Clark and Beerbower (1967) listed only a single specimen of Ischyromys, the Yoder local fauna has 24 rodent specimens representing 4 species (Kihm, 1987) and the McCarty's Mountain local fauna has approximately 225 specimens representing 7 species (A. Tabrum, pers. comm. 2009).

KIHM—CHADRONIAN RODENTS FROM NORTH DAKOTA

The lower Flagstaff Rim fauna contains 11 species (Emry, 1992). In comparison, the middle Chadronian rodent fauna is much better represented. The Calf Creek local fauna has more than 500 specimens representing at least 8 taxa (Storer, 1978) and the Raben Ranch local fauna has more than 3000 rodent specimens which Ostrander (1980) assigned to 30 taxa. The Medicine Pole Hills rodent fauna may look more similar to middle Chadronian faunas, at least in part, because of this sample bias. This would only be true if the rodent fauna of the late early Chadronian is incompletely known and if that unknown fauna looks similar to the middle Chadronian rodent fauna. At this time, the age of the Medicine Pole Hills local fauna could be considered either late early Chadronian based on Leptomeryx yoderi or middle Chadronian based on the similarity of the described rodents. The third alternative was suggested by Storer (1996) in stating that the Calf Creek local fauna may be intermediate between the late early Chadronian McCarty's Mountain and middle Chadronian Pipestone Springs local faunas. The Medicine Pole Hills might also represent an intermediate fauna similar to the Calf Creek local fauna. If the Calf Creek and Medicine Pole Hills faunas represent an intermediate stage, the occurrence of Leptomeryx mammifer in the Calf Creek fauna and L. yoderi in the Medicine Pole Hills fauna would suggest that the Medicine Pole Hills fauna is older than the Calf Creek fauna.

ACKNOWLEDGEMENTS The author would like to thank Messrs. Bill Simpson and Paul Mayer of the Field Museum of Natural History, Dr. Harold Bryant and Ms. Lee Ann Wright of the Royal Saskatchewan Museum for access to specimens. Mr. Guy Hanley of Minot State University produced the photographs. Mr. Jeff Oakland of Rhame, North Dakota allowed the collection of material on his lands and Mr. Dean Pearson of the Pioneer Trails Regional Museum aided in the collection of specimens as well as arranging the loan of specimens for study. Without all of their cooperation, this study would not have been possible. Drs. William Korth of the Rochester Institutute for Vertebrate Paleontology, John E. Storer and Robert J. Emry reviewed the manuscript and provided salient comments that improved the document. LITERATURE CITED Alf, R. 1962. A new species of the rodent Pipestoneomys from the Oligocene of Nebraska. Breviora 172:1-7.

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Black, C. C. 1965. Fossil mammals from Montana. Part 2. Rodents from the early Oligocene Pipestone Springs local fauna. Annals of Carnegie Museum 38(1):1-48. Burke, J. J. 1936. Ardnyomys and Desmatolagus in the North American Oligocene. Annals of Carnegie Museum 25:135-154. Burke, J. J. 1938. A new cylindrodont rodent from the Oligocene of Nebraska. Annals of Carnegie Museum 27:255-274. Clark, J. 1937. The stratigraphy and paleontology of the Chadron Formation in the Big Badlands of South Dakota. Annals of the Carnegie Museum 35:262-350. Clark, J. and J. R. Beerbower, 1967. Geology, paleoecology, and paleoclimatology of the Chadron formation. Pp. 21-74 in J. Clark, J. R. Beerbower, and K. K. Kietzke (eds.), Oligocene sedimentation, stratigraphy, paleoecology and paleoclimatology in the Big Badlands of South Dakota. Fieldiana: Geology Memiors 5:1-158. Donohoe, J. C. 1956. New aplodontid rodent from Montana Oligocene. Journal of Mammalogy 37(2):264-268. Emry, R. J., 1992. Mammalian range zones in the Chadronian White River Formation at Flagstaff Rim, Wyoming. Pp. 106-115 in D. R. Prothero and W. A. Berggren (eds.), Eocene-Oligocene Climatic and Biotic Evolution. Princeton University Press. Emry, R. J., and W. W Korth. 1996. Cylindrodontidae. Pp. 399-416 in D. R. Prothero and R. J. Emry (eds.), The Terrestrial Eocene-Oligocene Transition in North America. Cambridge University Press. Heaton, T. H. and R. J. Emry. 1996. Leptomerycidae. Pp. 581-608 in D. R. Prothero and R. J. Emry (eds.), The Terrestrial Eocene-Oligocene Transition in North America. Cambridge University Press. Kihm, A. J. 1987. Mammalian paleontology and geology of the Yoder Member, Chadron Formation, east-central Wyoming. Pp. 28-45 in J.E. Martin and G.E. Ostrander (eds.), Papers in vertebrate paleontology in honor of Morton Green. Dakoterra 3:1-122. Kihm, A. J. and K. K, Schumaker. 2008. Domnina (Mammalia, Soricomorpha) from the latest Eocene (Chadronian) Medicine Pole Hills local fauna of North Dakota. Paludicola 7(1):26-36. Korth, W.W. 1992. Cylindrodonts (Cylindrodontidae, Rodentia) and a new genus of eomyid, Paranamatomys, (Eomyidae, Rodentia) from the Chadronian of Sioux County, Nebraka.

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Transactions of the Nebraska Academy of Sciences 19:75-82. Korth, W. W. 1994. The Tertiary Record of Rodents in North America. Plenum Press, 319 pp. Lambe, L. M. 1908. The Vertebrata of the Oligocene of the Cypress Hills, Saskatchewan. Contributions to Canadian Palaeontology 3(4):164. Matthew, W. D. 1905. Notice of two new genera of mammals from the Oligocene of South Dakota. American Museum of Natural History Bulletin 21(3):21-26. Matthew, W. D. and W. Granger. 1925. New creodonts and rodents from the Ardyn Obo Formation of Mongolia. American Museum Novitates no. 193:1-7 pp. Murphy, E. C., J. W. Hoganson , and N. F. Forsman. 1993. The Chadron, Brule and Arikaree Formations in North Dakota. North Dakota Geological Survey Report of Investigation no. 96:1-144. Ostrander, G. 1980. Mammalia of the early Oligocene (Chadronian) Raben Ranch local fauna of northwestern Nebraska. Unpublished M.S. thesis, South Dakota School of Mines and Technology. 288 pp. Ostrander, G. 1983. New early Oligocene (Chadronian) mammals from the Raben Ranch local fauna, northwest Nebraska. Journal of Paleontology 57(1):128-139. Prothero, D. R. and R. J. Emry. 2004. The Chadronian, Orellan, and Whitneyan North American Land Mammal Ages. Pp. 156-168 in M. O. Woodburne (ed.) , Late Cretaceous and Cenozoic Mammals of North America, Biostratigraphy and Geochronology. Columbia University Press. Russell, L. S. 1954 Mammalian fauna of the Kishenehn Formation, southeastern British Columbia. Bulletin of the National Museum of Canada 132:92-111. Russell, L. S. 1972. Tertiary mammals of Saskatchewan. Part II: The Oligocene fauna, non-ungulate orders. Royal Ontario Museum Life Sciences Contribution 84:1-97. Schumaker, K. K. and A. J. Kihm. 2006. Multituberculata from the Medicine Pole Hills local fauna (Chadronian) of Bowman County, North Dakota. Paludicola 6(1):9-21.

Storer, J. E. 1978. Rodents of the Calf Creek local fauna (Cypress Hills Formation, Oligocene, Chadronian), Saskatchewan. Saskatchewan Museum of Natural History Contributions 1:154 pp. Storer, J. E. 1988. The rodents of the Lac Pelletier lower fauna, late Eocene (Duchesnean) of Saskatchewan. Journal of Vertebrate Paleontology 8(1):84-101. Storer, J. E. 1996. Eocene-Oligocene faunas of the Cypress Hills Formation, Saskatchewan. Pp. 240-261 in D. R. Prothero and R. J. Emry (eds.), The Terrestrial Eocene-Oligocene Transition in North America. Cambridge University Press. Tabrum, A. R., D. R. Prothero , and D. Garcia. 1996. Magnetostratigraphy and biostratigraphy of the Eocene-Oligocene transition, southwestern Montana. Pp. 278-311 in D. R. Prothero and R. J. Emry (eds.), The Terrestrial EoceneOligocene Transition in North America. Cambridge University Press. Webster, J. R. and A. J. Kihm. 2009. Heavy mineral analysis and correlation of late Eocene sandstones of the Williston Basin. Geological Society of America Abstracts with Programs 41(7): 690. West, C. M. and W. W. Korth. 1994. First record of Pipestoneomys (Mammalia: Rodentia) from the Orellan (Oligocene). Transactions of the Nebraska Academy of Sciences 21:147-150. Wood, A. E. 1937. The mammalian fauna of the White River Oligocene. Part II. Rodentia. Transactions of the American Philosophical Society 28:155-269. Wood, A. E. 1974. Early Tertiary vertebrate faunas Vieja Group Trans-Pecos Texas: Rodentia. Texas Memorial Museum Bulletin 21:1-112. Wood, A. E. 1980. The Oligocene rodents of North America. Transactions of the American Philosophical Society 70:1-68. Wood, A. E. and R. W. Wilson. 1936. A suggested nomenclature for the cusps of the cheek teeth of rodents. Journal of Paleontology 10(5):388-391.

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HERPETOFAUNA OF LATE MIOCENE SAPPA CREEK FAUNA, NORTHWESTERN KANSAS J. Alan Holman1*, Leslie P. Fay 2, and William W. Korth 3 1

Michigan State University Museum, West Circle Dr., East Lansing, Michigan 48824-1045, *deceased 2 Illinois State Museum, Research & Collection Center, 1011 E Ash, Springfield, Illinois 62703 3 Rochester Institute of Vertebrate Paleontology, 265 Carling Road, Rochester, New York

ABSTRACT A diverse herpetofauna from the Clarendonian to Hemphillian Sappa Creek local fauna, Kansas, is described. The occurrence of biostratigraphically diagnostic amphibians and reptiles from the Clarendonian part of the sequence support the earlier age determination based on mammalian species. The earliest occurrence of the rattlesnake Crotalus is reported from the lower part of the Clarendonian section. Composition of the herpetofauna suggests a paleoenvironment with a warm, dry climate with at least seasonal surface water available.

SYSTEMATIC PALEONTOLOGY Class Amphibia Linneaus, 1758 Order Caudata Oppel, 1811 Family Ambystomatidae Hallowell, 1856 Ambystoma Tschudi, 1838 Ambystoma maculatum (Shaw, 1802) (Figure 1A, B)

INTRODUCTION The rocks exposed along Sappa Creek in northwestern Kansas have yielded numerous fossil mammals (Korth, 2004; Korth and Baskin, 2009). The stratigraphic section spans the boundary between the Clarendonian and Hemphillian land mammal ages, ranging from approximately 9.5 to 9.0 mya (Korth, 2004). Although much less common, several specimens of amphibians and reptiles have been collected from the same quarries. Screenwashing of microvertebrates has yielded very few micromammals, but has produced all of the elements of the herpetofauna except the large land tortoises. The specimens described below have been collected from the previously reported fossil quarries in Decatur and Rawlins counties, Kansas (Korth, 2004). The early Hemphillian quarries that have yielded the reptile and amphibian specimens described below are Anderson Quarries #1 and #2, and the late Clarendonian quarries are Katy’s Quarry, Mumm Quarry and Yoos Quarry (see Korth, 2004). Sappa Creek specimens described herein reside at the Carnegie Museum of Natural History (CM), Pittsburgh. Taxonomy for extant genera and species follows Crother (2008), and general geographic ranges of extant taxa follow Conant and Collins (1998). Measurements (in millimeters) were made with an optical micrometer calibrated in a binocular microscope at 9X magnification.

Specimens—CM 76280 - trunk vertebra; CM 76281- trunk vertebra. Locality—Mumm Quarry Comments—Tihen (1958) devised ratios of linear vertebral measurements to distinguish among morphological groups within Ambystoma. As the ranges of ratios overlap between groups, large sample sizes and corroboration with additional morphologic features are prudent in assigning fossil specimens. The Mumm vertebral ratios are 2.0/1.5 (CM76280) and 2.2/1.4 (CM76281). The former plots within the published A. opacum and A. tigrinum ranges, the latter just within the A. maculatum range, but also within A. opacum and A. tigrinum. Holman (2006:142) considered the combination of upswept posterior neural arch and large to very large size of trunk vertebrae “essential” for assignment to the A. tigrinum-group. Ambystoma opacum-group trunk vertebrae also exhibit somewhat upswept posterior arches, but are smaller than A. tigrinum (Holman, 2006). The Mumm specimens are relatively large (4.4, 4.9 mm centrum length), but do not exhibit pronounced upsweep of the 91

 

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FIGURE 1. Vertebrae of Ambystoma maculatum and indeterminate Pelobatid. A, B, A. maculatum, CM 76280, trunk vertebra. A, anterior view. B, dorsal view. C, ?Pelobatidae, genus and species indeterminate, CM 83047, vertebral centrum (ventral view). Bar scale = 5 mm. _____________________________________________________________________________________________________________________

Locality—Mumm quarry Comments—These two specimens are sufficiently complete for specific assignment.

neural arch, aligning them with the A. maculatumgroup. As the two vertebrae are much larger than other members of A. maculatum-group, including the Clarendonian-Hemphillian species A. minshalli Tihen and Chantell, we assign them to A. maculatum. This extant species has also been recorded from the Clarendonian WaKeeney local fauna of nearby Trego County, Kansas (Holman, 1975). A. priscum Holman, of the medial Barstovian of Nebraska (Holman, 1987), is larger than A. maculatum from Sappa Creek, but does not compare favorably in Tihen’s ratios. Present western range limit of A. maculatum is approximately 500 km east of the fossil locality.

Order Anura Rafinesque, 1815 Family Pelobatidae Bonaparte, 1850 ?Pelobatidae, genus and species indeterminate (Figure 1C) Specimen—CM 83047—vertebral centrum [centrum width = 1.8mm, centrum length = 2.0 mm], missing neural arch, right prezygopophysis, postzygopophyses, and distal transverse processes. Locality—Mumm quarry Comments—The vertebra is biconcave, characteristic of the third presacral of North American adult microhylids (Holman, 2006:184). However, this specimen is much larger than modern Gastrophryne,

Ambystoma sp. indet. Specimens—CM 76284 - R humerus, distal fragment; CM 76289 – vertebral centrum.

 

not

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  and the transverse processes leave the centrum laterally, not with a dorsally angled orientation. It most closely matches Scaphiopus or Spea and may represent a late-juvenile individual based on size. Anura, indeterminate Specimen—CM 76291—right tibiofibula fragment, central shaft with distal portion. Locality—Mumm quarry. Comments—This bone is not sufficiently complete for further identification. Additional collecting from the Sappa Creek localities may produce anuran material identifiable to genus or species level. All extant frog families of the Great Plains are known to have occurred in the region during the Clarendonian/Hemphillian interval (Holman 2006; Parmley et al., 2010). Class Reptilia Laurenti, 1768 Order Testudines Batsch, 1788 Family Testudinidae Gray, 1825 Hesperotestudo sp. indet. (large) Specimens—CM 76171 – medial pleural fragment; CM 76207 – limb element fragment; CM 73521 – limb element fragment. Locality—Anderson #1 quarry. Specimens—CM 76163 – 2nd right costal fragment, CM76164 – 3rd neural, CM 76165 – posterior costal fragment, CM 76166 – left peripheral medial fragment, CM 76167 – costal fragment, 76168 - left peripheral medial fragment, CM 76169 - costal fragment, CM 76218 – left scapula with both articular ends missing, CM 70378 - small indeterminate shell fragment. Locality—Mumm Quarry Hesperotestudo sp. indet. (small) Specimen—CM 76170 – pleural fragment. Locality—Katy’s quarry Comments—Holman (1975:59) reported Geochelone (=Hesperotestudo) orthopygia (Cope), a large-shelled land tortoise, and a second, smaller testudinid species represented by indeterminate material, from the WaKeeney local fauna. Wild Horse Creek #1, a Clarendonian-Hemphillian local fauna from Oklahoma, has also yielded large and small testudinid morphs (Czaplewski et al., 2001). Although none of the Sappa Creek quarries have yet produced sufficient material for specific identifications, the Anderson #1 and Mumm animals (large morph) were much larger than the Katy’s tortoise.

Testudinidae, gen. et sp. indet. (Figure 2C) Specimens—CM 76172 – entoplastron; CM 83048 – L ulna. Locality—Mumm Quarry. Comments—Relatively small size and particularly the scute pattern make assignment of the entoplastron equivocal between Gopherus and Hesperotestudo respectively, based on comparisons with modern and fossil material. A small individual of the former or juvenile of the latter could be represented. The ulna is also equivocal based on size, but is morphologically distinct from non-testudinid turtles. Tortoise material is almost ubiquitous among Great Plains Tertiary local faunas. Testudines indet. Specimen—CM 70379 - plastral fragment. Locality—Yoos quarry Comments—This bone is not sufficiently complete for further identification, but likely is a testudinid or emydid turtle. Order Sauria McCartney, 1802 Family Teiidae Cope, 1871 Aspidoscelis Fitzinger, 1843 Aspidoscelis sp. indet. (Figure 2A, B) Specimens—CM 76273 – trunk vertebra, CM 76275 – trunk vertebra, CM 76278 – right dentary, CM 76279 – left dentary, CM 76282 – trunk vertebra, CM 76285 – left tibia, CM 76286 – left humerus, CM 76287 – left femur. Locality—Mumm Quarry Comments—The material compares favorably with modern Aspidoscelis, but we are unable to assign it confidently to any one of the many species of Aspidoscelis including A. bilobatus (Taylor). Holman (1975) reports Aspidoscelis (as Cnemidophorus) cf. A. sexlineatus (Linneaus) from the WaKeeney local fauna. Order Serpentes Linneaus, 1758 Family Colubridae Oppel, 1811 Subfamily Xenodontinae Cope, 1893 Heterodon Latreille in Sonnini and Latreille, 1801 or Paleoheterodon Holman, 1964 (Figure 3) Specimen—CM 76274 – trunk vertebra. Locality—Mumm Quarry Comments—“The fact that subtle vertebral differences between genera of snakes such as

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  Xenodontinae, gen. et sp. indet. Specimen—CM 76276 – trunk vertebra. Locality—Mumm Quarry Comments—A very small xenodontine featuring low neural arch and a (damaged) neural spine that was apparently very long and low. It does not compare favorably with known North American Late Miocene diminutive xenodontines, such as Diadophis, or with other Neogene or modern xenodontines from the Great Plains. It may represent a previously unknown genus. Colubridae, gen. and sp. indet. (Figure 4) Specimen—CM 73519 – trunk vertebra. Locality—Katy’s Quarry Comments—This specimen is from a juvenile individual, suggestive of a lampropeltine. Colubridae, genus and species indeterminate Specimen—CM 76277 – trunk vertebra in three fragments. Locality—Anderson Quarry #2 Comments—Representing a very small snake, the specimen is not sufficiently complete for further identification. Family Viperidae Oppel, 1811 Subfamily Crotalinae Oppel, 1811 Crotalus Linneaus, 1758 Crotalus sp. indet. (Figure 5) FIGURE 2. Aspidoscelis and undetermined testudinid. A, B, Aspidoscelis sp. indet., CM 76278, right dentary. A, lateral view. B, medial view. C, Testudinidae, gen. and sp. undet. CM 76172 , entoplastron (ventral view). Bar scale = 1 mm.

Specimen—CM 76272 – trunk vertebra. Locality—Yoos Quarry Comments—This vertebra has multiple paracotylar foramina, characteristic of Crotalus, but not Agkistrodon or Sistrurus. Neural spine and zygosphenes are not complete enough to indicate species identity. Holman (2000) and Parmley and Holman (2007) recognized Crotalus from the middle and late Hemphillian, and Parmley and Hunter (2010:539) questionably referred two trunk vertebrae to “cf. Crotalus sp. indet.” from the late Clarendonian. The Yoos Quarry specimen is the oldest definite reported Crotalus.

____________________________________________ Paleoheterodon and Heterodon may be accompanied by very marked differences in their individual skull bones is provocative” (Holman, 2000:133). This single vertebra is an insufficient sample to attempt generic identity. A larger sample from Sappa Creek may offer insight into the Heterodon/Paleoheterodon lineage, as there is a temporal, but not spatial, overlap between the two genera in the Hemphillian record. Parmley and Hunter (2010) noted that there was no morphological difference between the trunk vertebrae of Paleoheterodon and Heterodon, thus making a generic distinction on the Kansas material impossible.

 

DISCUSSION Mammalian biostratigraphy indicates that the Clarendonian-Hemphillian transition is represented within the sequence of quarries in the North and Middle Fork of the Sappa Creek sections (Korth,

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FIGURE 3. Heterodon or Paleoheterodon, CM 76274, trunk vertebra. A, Dorsal view. B, ventral view. C, anterior view. D, posterior view. E, left lateral view. Bar scale = 1 mm.

________________________________________________________________________________________________ 2004). Taxonomically and potentially biostratigraphically diagnostic amphibian and reptile fossils have been recovered from the Clarendonian part of the sequence (Mumm and Yoos quarries) and are consistent with this assignment (Table 1). No early

Miocene (sensu Holman, 2000) faunal elements have been recovered. Larger samples of several known taxa (especially xenodontine snakes and Hesperotestudo tortoises) may contribute to understanding of those

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FIGURE 4. Colubridae, gen. and sp. indet., CM 73519, trunk vertebra. A, Dorsal view. B, ventral view. C, anterior view. D, posterior view. E, right lateral view. Bar scale = 1 mm. ______________________________________________________________________________________________________________________

lineages, as well as further refining placement of Sappa Creek localities within the Great Plains Miocene. Occurrences of Crotalus rattlesnakes have not been previously published from localities older than the middle to late Hemphillian of Nebraska (Holman, 2000; Parmley and Holman, 2007), indicating that the Yoos quarry specimen is the oldest known record of the genus.

 

Although only a few distinctly identifiable forms are represented in the known Sappa Creek samples, some ecological parameters can be suggested. The presence of a large Hesperotestudo morph limits paleoenvironmental temperature reconstruction to no lower than 0˚C because, unlike smaller tortoises and turtles, this large tortoise could not burrow to escape adverse conditions (Hibbard, 1960). The modern

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FIGURE 5. Crotalus sp. indet., CM 76272, trunk vertebra. A, Dorsal view. B, ventral view. C, anterior view. D, posterior view. E, right lateral view. Bar scale = 1 mm.

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  LITERATURE CITED

representatives of other reptiles identified to genus or species prefer grassy (?Heterodon) to semi-xeric habitats. Kansas Aspidoscelis have temperature optimums approaching 34˚C (Collins, 1982:160). No obligate aquatic taxa have been recognized, but the amphibians required seasonal surface water for egglaying. ____________________________________________

Collins, J. T., 1982. Amphibians and reptiles in Kansas; University of Kansas Museum of Natural History, Public Education Series 8, 356p. Conant, R., and J. T. Collins, 1998. A Field Guide to Reptiles and Amphibians – Eastern and Central North America (3rd ed. expanded); Boston & New York, Houghton Mifflin, 615p. Crother, B. I., (ed.), 2008. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, pp. 1-84, SSAR Herpetological Circular 37. Czaplewski, N. J., J. P. Thurmond, D. G. Wyckoff, 2001. Wild Horse Creek #1: A Late Miocene (Clarendonian-Hemphillian) vertebrate fossil assemblage in Roger Mills County, Oklahoma; Oklahoma Geology Notes 61(3):60-67. Hibbard, C. W., 1960. An interpretation of Pliocene and Pleistocene climates in North America; Annual Report, Michigan Academy of Science, Arts, and, Letters 64:5-30, Holman, J. A. 1975. Herpetofauna of the WaKeeney local fauna (Lower Pliocene: Clarendonian) of Trego County, Kansas; University of Michigan Museum of Paleontology, Papers on Paleontology No. 12: 49-66. Holman, J. A. 1987. Herpetofauna of the Egelhoff site (Miocene: Barstovian) of south-central Nebraska; Journal of Vertebrate Paleontology 7:109-120. Holman, J. A. 2000. Fossil snakes of North America: origin, evolution, distribution, paleoecology; Indiana Press, Bloomington, 357p. Holman, J. A. 2006. Fossil salamanders of North America; Indiana Press, Bloomington, 232p. Korth, W. W. 2004. Preliminary determination of the age of the Sappa Creek local fauna, northwestern Kansas; Paludicola 4(4):115124. Korth, W. W. and J. A. Baskin. 2009. A new species of Leptarctus (Carnivora, Mustelidae) from the late Clarendonian (late Miocene) of Kansas. Annals of Carnegie Museum 78:2944. Parmley, D. and J. A. Holman. 2007. Earliest rossil record of a pigmy rattlesnake (Viperidae: Sistrurus Garman). Journal of Herpetology 41:141-144. Parmley, D. and K. B. Hunter. 2010. Fossil snakes of the Clarendonian (late Miocene) Pratt Slide local fauna of Nebraska, with the description

TABLE 1. Herpetofauna from Sappa Creek local fauna by quarries (arranged in chronological order). Hemphillian Quarries Anderson # 2 Colubridae gen. et. sp. indet. Anderson #1 Hesperotestudo, sp. indet. Clarendonian Quarries Katy's Hesperotestudo, sp. indet. [small] Colubridae gen. et. sp. indet. Mumm Hesperotestudo, sp. indet. Testudinidae Aspidoscelis sp. indet. ?Heterodon or Paleoheterodon Xenodontinae, gen. et. sp. indet. Ambystoma maculatum Ambystoma sp. indet. Anura Anura, ?Pelobatidae Yoos Testudines Crotalus, sp. indet. ____________________________________________

ACKNOWLEDGEMENTS Amy Henrici of Carnegie Museum and Laura Abraczinskas of Michigan State University Museum were most helpful to LPF in taking over where JAH left off with the Sappa Creek herps. Dennis Parmley of Georgia College and State University contributed his expertise on Miocene snakes. Much of LPF’s contribution was made possible by a sabbatical leave from Rock Valley College, Rockford, Illinois. Earlier versions of this paper were critically read by Drs. D. Parmley and Smith.

 

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  of a new natricine colubrid. Journal of Herpetology 44:526-543. Parmley, D. K. B. Hunter and J. A. Holman. 2010. Fossil frogs from the Clarendonian (late Miocene) of Oklahoma, U>S>A> Journal of Vertebrate Paleontology 30:1879-1883.

Tihen, J. A. 1958. Comments on the Osteology and phylogeny of ambystomatid salamanders; Bulletin of the Florida State Museum Biological Sciences 3:1-50.

Paludicola 8(2):100-105 April 2011 © by the Rochester Institute of Vertebrate Paleontology

LARGE ICHTHYOSAURIAN REMAINS FROM THE LA CASITA TYPE LOCALITY (TITHONIAN, UPPER JURASSIC), COAHUILA, MEXICO Marie-Céline Buchy1 and Anabel Covarrubias Cervantes2 1- Museo del Desierto, Prol. Perez Treviño 3745, Parque Las Maravillas, CP 25015, Saltillo, Coahuila, Mexico. Current address: 1, Tossen Hat, F-22140 Kermoroc’h, France. [email protected] 2- Unidad Académica Multidisciplinaria Zona Huasteca - UASLP, Cd. Valles, San Luis Potosí, Mexico.

ABSTRACT The specimen described here (CPC 306) is the first and only vertebrate from the Tithonian La Casita type locality in southern Coahuila, Mexico. The specimen comprises at least 42 centra from the posterior trunk and anterior tail, as well as neural arch and rib fragments, of an ophthalmosaurid ichthyosaur. The size of the centra are comparable to Ophthalmosaurus natans, but the pattern of variation in the centrum height/centrum length ratio and the values of that ratio are more similar to O. icenicus. The preservation prevents a more precise taxonomic identification. Ophthalmosaurus has been reported from Gomez Farias, a site further south in Coahuila. The Mexican Gulf ichthyosaurs show no signs of endemism and have a lower diversity than elsewhere in the world at the time. Thus every specimen from the Gulf at present is important, pending futher discoveries in the region.

In July 2008, the senior author was allowed by COECYT to excavate and prepare the large ichthyosaur now numbered CPC 307 (Buchy and López Oliva 2009; Buchy et al. 2009). Due to the absence at MUDE of a catalogue of unpublished specimens, the origin of many specimens in the collection is known only if the person who found them or someone who heard about it is available for consultation. When the project was submitted to COECYT, confusion occurred between the locality of CPC 307 and that of CPC 306. Only when the project was granted was the senior author made aware of the confusion, that was clarified by a first visit to the excavation site of CPC 307 (of a late Tithonian age according to Buchy and López Oliva 2009), located a few kilometers south of the site of CPC 306. Preparation of CPC 306 was completed and the student exchange program Verano de la Ciencia from CONACYT provided the opportunity to study it. Systematic examination of the marine reptiles from the Late Jurassic Mexican Gulf conducted during the last decade yielded various ichthyosaurs, and therefore a (still in nascent stage) taxonomical framework within which the specimen herein described can now be assessed.

INTRODUCTION A decade of investigation of Upper Jurassic outcrops in northeast Mexico has yielded a rich assemblage of marine reptiles that populated the Mexican Gulf (e.g. Buchy 2007). Based on the study of invertebrates and microfossils, the Gulf appears to have been isolated from the opening Atlantic until the Berriasian (e.g. Goldhammer 1999; Goldhammer and Johnston 2001). The study of marine reptiles tends to confirm some endemism (see a review in Buchy 2007), however, many specimens are yet to be studied to confirm and characterize the peculiarity of the vertebrate assemblage. Furthermore, elucidation of the phylogenetic affinities of the specimens is pending the results of preparation and anatomical studies. Fish remains are also known from the same sites, but their study has not been initiated yet. During the last decade of investigation, fieldwork was undertaken revealing new material, however various institutional and private collections also yielded specimens of value that had gone ignored for years. Among those is the presently described specimen, now CPC 306 (at MUDE). CPC 306 was reported as coming from the La Casita type locality in southern Coahuila (Imlay 1936; Aguirre Garza et al. 2000:fig. 1) and to our knowledge, it is indeed the first and only vertebrate remains described from this locality. It was discovered by a field party of UANL-FCT, and then excavated with the help of MUDE and UNAM personnel in spring 2000. The specimen was partly prepared and subsequently attributed by its discoverers to the genus Ichthyosaurus (Aguirre Garza et al. 2000); after this preliminary report, preparation was never completed.

Abbreviations—COECYT, Consejo Estatal de Ciencia y Tecnologia Coahuila; CONACYT, Consejo Nacional de Ciencia y Tecnología; MUDE, Museo del Desierto, Saltillo, Coahuila; UANL-FCT, Universidad Autónoma de Nuevo León, Facultad de Ciencias de la Tierra, Linares, Nuevo León; UNAM, Universidad Nacional Autónoma de México.

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FIGURE 1: Map of Mexico (insert) and detail of southeast Coahuila and central Nuevo León; the area of the find is shown by a star. _____________________________________________________

SYSTEMATIC PALEONTOLOGY Order Ichthyosauria de Blainville, 1835 Family Ophthalmosauridae Baur, 1887 Ophthalmosauridae indet. Material—CPC 306 (Figures 2, 3). At present, the specimen comprises at least 42 centra from the posterior part of the trunk and anterior part of the tail and numerous non-matching fragments. The anteriormost centra are partly obscured by rib and neural arch fragments. Origin—Tithonian La Casita type locality, Municipio de General Cepeda, Coahuila, Mexico (Aguirre Garza et al. 2000:fig. 1). Preservation—The specimen was collected as isolated fragments and at least one plaster jacket which still houses the posterior-most part of the specimen (21 centra included in the count of 42). It was partly prepared then stored in that condition at MUDE for some years, during which time it was moved around according to space requirements. It is unknown if any of the specimen was lost during these movements. At least 21 additional centra (Table 1) are documented outside this plaster jacket. The original publication (Aguirre Garza et al. 2000) mentioned 30 centra. The posterior-most part of the specimen was still partly unprepared in its (open) plaster jacket when it was 'rediscovered' in 2008, but it remains unclear whether the published 30 centra correspond only to the centra outside of the jacket (in this case, several were lost subsequently or are now preserved as non-matching fragments), or are a very

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rough estimate of these plus what was inside the jacket. The centra are partly articulated (see Table 1 and Figure 2). The bone is very weathered, and to prevent further damage it was coated with transparent epoxy resin; it is unclear whether this resin is stable over time. Owing to the poor standards of the collection of fossils at MUDE under the present administration, and the risk of the fossil being further damaged by being moved or when being sent for exhibition, it was considered the only option to stabilize and preserve it. Description—The centra are typically ichthyosaurian in shape (e.g. McGowan and Motani 2003). The disarticulated centra of CPC 306 were ordered by comparison with CPC 307, and were consequently numbered, knowing that some centra may be missing in between (Table 1). As is visible on the articulated specimen CPC 307 (currently under study), in the anterior part of the vertebral column, the dia- and parapophyses are clearly separated; in the pelvic region, they migrate ventrally and toward one another. They fuse on centrum 47 and constitute a high oval articular facet for the rib, whereas further posteriorly (serial position unknown, some vertebrae missing in between) the facet becomes subcircular or long oval. The dia- and parapophyses of CPC 306 fuse on the 10th preserved centrum. The articular facet becomes long oval on the 16th preserved centrum. The centrum of CPC 306 where the fusion occurs is about 44 mm long and 100 mm high; that of CPC 307 is about 50 mm long and 125 mm high. Taking into account the slight distortion the latter underwent, both centra share the same length to height proportion (about 0.4). DISCUSSION The original attribution of CPC 306 to Ichthyosaurus (Aguirre Garza et al. 2000) cannot be sustained; CPC 306 likely represents an ophthalmosaurid on stratigraphic grounds (McGowan and Motani 2003). The dimensions of CPC 306 (Table 1) exceeds in size that of specimens attributed to Ophthalmosaurus icenicus (e.g. Motani 1999; Massare et al. 2006), but compare closely in that respect to specimens referred to O. natans by Massare et al. (2006). Few adequately preserved centra of CPC 306 allow to determine the ratio centrum height/centrum length (CH/CL, see Massare et al. 2006; Table 1). The values of this ratio for centra from the posterior dorsal region (anterior to the 10th preserved centrum) are lower than those documented for O. icenicus by Massare et al. (2006), coming closer to the values for O. natans as given by these authors. In contrast, the high value of CH/CL for the 18th preserved centrum (3.14; centrum from the anterior caudal region) and pattern of variation of CH/CL along the specimen (Table 1) is more similar

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TABLE 1. Type of preservation and dimensions of the centra of CPC 306 in mm. All measurements are approximate due to poor preservation. Dia- and parapophyses fuse on the 10th preserved centrum.

centrum number comments 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

isolated three clusters of respectively four, six and two articulated centra

isolated cluster of four articulated centra

cluster of three articulated centra centra still in plaster jacket; centra 29, 30 and 34 are documented as imprints on the jacket but are now fragments

height at the level of the neural canal / / / / 108 108 / / / 100 100 100 104 / / / / 107 / / / 100 100 / / / / 95 / / 95 / / / 100 / 83 / / / / /

ventral length 43 45 45 / 46 46 44 44 43 44 44 41 42 45 42 38 38 34 38 38 40 / 45 40 39 42 40 40 / / 40 40 39 / 37 / 37 36 33 34 31 /

centrum height / length

2.34 2.34

2.27 2.27 2.43 2.47

3.14

2.22

2.37

2.37

2.7 2.24

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FIGURE 2: CPC 306, right lateral view of the 42 centra that can be ordered in the vertebral series (see text and Table 1). Scale bar 50 mm. ____________________________________________________________________________________________________________________

FIGURE 3: CPC 306, A, detail of centra 6 to 11 (see text and Table 1) in right ventrolateral view and B. interpretative drawing. C. centrum 6 in cranial view and D interpretative drawing. Scale bar 50 mm ____________________________________________________________________________________________________________________

to the values and variation of CH/CL for O. icenicus (Massare et al. 2006), despite size similarity to O. natans. The nature and poor preservation of CPC 306 prevents a more precise taxonomic identification at present. From the Late Jurassic Mexican Gulf, CPC 307 represents a large form, close to Brachypterygius according to the anatomy of its forefin (Buchy and López Oliva 2009; material under study). The genus Ophthalmosaurus has been documented, likely represented by the ubiquitous, type species O. icenicus (Buchy 2010), coming from near Gomez Farías, a site further south in Coahuila that is considered a Lagerstätte owing to its richness in marine vertebrates (Buchy et al. 2006a). Additionally, from Gomez Farías a unique, isolated centrum from the posterior part of the dorsal region (having separated dia- and parapophyses located ventrally on the centrum) exhibits dimensions that also exceed those commonly attributed to O. icenicus. This specimen, CPC 488 (at MUDE), has a height of 92 mm and a length of 35 mm, with a length to height ratio of 0.38, and is therefore similar to CPC 306 and CPC 307. CPC 488 likely indicates

the presence in Gomez Farías of a second type of ichthyosaur possibly close (at least in size) to CPC 306 and 307. The individual age of CPC 306 compared to that of CPC 307 cannot be determined; based on its smaller size CPC 306 could indeed represent a juvenile of the taxon documented by CPC 307. Thus the diversity of ichthyosaurs from the Late Jurassic Mexican Gulf is much lower than what is reported from the rest of the world at the time (McGowan and Motani 2003; Fernández 2007). Compared to other groups of marine reptiles, e.g. thalattosuchians (see a review in Buchy 2007; Buchy et al. 2006b, 2007; Buchy 2008), the Mexican Gulf ichthyosaurs show no obvious sign of endemism, despite being (relatively) abundant. The current scarceness of diagnostic ichthyosaurian material from the Gulf is likely the reason (Buchy 2007). It should be noted that it was suggested that the Late Jurassic Mexican Gulf may have represented a 'nursery' for ubiquitous ichthyosaurs (Buchy 2010), in order to explain the preliminary observation that ichthyosaurs apparently do not show the same

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endemism as other marine reptile groups, invertebrates and microfossils. In any case, CPC 306, its finding and curation history do plead for a more thorough and professional search for ichthyosaurian remains from the Late Jurassic Mexican Gulf, as well as generally for more competent preparation and curation skills devoted to such fossils in Mexican Institutions in the future. It is essential to assess the actual diversity of ichthyosaurs there at the time, and to investigate whether or not the Gulf represented a 'nursery'. It is also essential to determine the origin, pattern, timing and dynamic of the population of the Gulf by the various groups of marine reptiles compared to what was deduced from (relatively) abundant invertebrates and microfossils. In this respect, awaiting further fieldwork, it should be considered that every marine reptile from the Gulf at present is important, keeping in mind what future research will hopefully yield as comparative material. ACKNOWLEDGEMENTS A decade of investigation of the Mexican marine reptiles was financed by DFG grants (FR1314/4-1, 6-1, 7-1, 9-1, 9-2) to E. Frey (Karlsruhe) and W. Stinnesbeck (Heidelberg) and COECYT Coahuila to MCB (grant COAH-2008C04-37). Thanks are also due to J. G. López Oliva (UANL-FCT) for access to specimens in his care and discussion and to A. H. González González (MUDE). Thanks to C. R. Delgado De Jesus (MUDE) for information about the original field campaign, and to S. J. Aguirre Garza, R. H. Peterson Rodríguez, J. A. Velasco Segura and G. C. Chavez (all UANL-FCT) and R. Hernández Rivera (UNAM) for having found the specimen and brought it to institutional collection. Further preparation was performed by J. A. Robledo García and A. I. Oyervides Salazar (both MUDE). The Verano de La Ciencia patronized by CONACYT was organized at MUDE by C. E. Luna Fuentes and M. R. Ovalle Martinez. The authors are indebted to the Curaduria de Plantas department of MUDE for the coffee breaks. The manuscript greatly benefited from comments of M. Fernández (La Plata) as reviewer and J.A. Massare (Brockport) as reviewer and Editor. LITERATURE CITED Aguirre Garza, S. J., R. H. Peterson Rodríguez, J. A. Velasco Segura, C. R. Delgado, and G. C. Chavez. 2000. Evidencia de un reptil marino del Jurásico superior en la Sierra de Parras, Coahuila, México. VII Congreso Nacional de Paleontologia, Sociedad Mexicana de Paleontologia, libro de resumenes: 115. Baur, G. 1887. Über den Ursprung der Extremitäten der Ichthyopterygia. Jahresberichte und

Mitteilungen des Oberrheinischen geologischen Vereines 20:17-20. Blainville, H. D. de. 1835. Description de quelques espèces de reptiles de la Californie, précédée de l'analyse d'un système général d'Erpetologie et d'Amphibiologie. Nouvelles Annales du Muséum National d'Histoire naturelle, Paris 4:233-296. Buchy, M.-C. 2007. Mesozoic marine reptiles from north-east Mexico: description, systematics, assemblages and palaeobiogeography. Unpublished PhD thesis, University of Karlsruhe, 98 p. Available online at: http://digbib.ubka.uni-karlsruhe.de/volltexte /1000007307 Buchy, M.-C. 2008. New occurrence of the genus Dakosaurus (Reptilia, Thalattosuchia) in the Upper Jurassic of north-eastern Mexico with comments upon skull architecture of Dakosaurus and Geosaurus. Neues Jahrbuch für Geologie und Paläontologie 249:1-8. Buchy, M.-C. 2010. First record of Ophthalmosaurus (Reptilia: Ichthyosauria) from the Tithonian (Upper Jurassic) of Mexico. Journal of Paleontology 84(1): 149-155. Buchy, M.-C. and J. G. López Oliva. 2009. Occurrence of a second ichthyosaur genus (Reptilia: Ichthyosauria) in the Late Jurassic Gulf of Mexico. Boletín de la Sociedad Geológica Mexicana 61(2): 233-238. Buchy, M.-C., Frey, E., Stinnesbeck, W. and A. H. González González. 2006a. A new Tithonian (Upper Jurassic) marine vertebrate concentration Lagerstätte in north-eastern Mexico. Hantkeniana 5:17-19. Buchy, M.-C., P. Vignaud, E. Frey, W. Stinnesbeck, and A. H. González González. 2006b. A new thalattosuchian crocodyliform from the Tithonian (Upper Jurassic) of north-eastern Mexico. Comptes Rendus Palevol 5:785794. Buchy, M.-C., W. Stinnesbeck, E. Frey, and A. H. González González. 2007. Première mention du genre Dakosaurus (Crocodyliformes, Thalattosuchia) dans le Jurassique supérieur du Mexique. Bulletin de la Société géologique de France 178(5): 391-397. Buchy, M.-C., Z. M. Casas García, C. R. Delgado de Jesús, J. Flores Medina, J. G. López Oliva, A. I. Oyervides Salazar, and J. A. Robledo García. 2009. The El Sombrero ichthyosaur: a second genus of ichthyosaurs (Reptilia: Ichthyopterygia) in the Late Jurassic Mexican Gulf. XI Congreso nacional de paleontología, Querétaro (Mexico), 25-27 February 2009, Abstract Book: 91. Fernández, M. S. 2007. The Ichthyosauria, p. 271291. In Z. Gasparini, L. Salgado and R.

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Coria, eds. Patagonian Mesozoic Reptiles, Indiana University Press. Goldhammer, R. K. 1999. Mesozoic sequence stratigraphy and paleogeographic evolution of north east Mexico, p. 1-31. In C. Bartolini, J. L. Wilson, and T. F. Lawton, eds. Sedimentary and tectonic history of north central Mexico. Geological Society of America Special Paper, 340. Goldhammer, R. K., and C. A. Johnson. 2001. Middle Jurassic – Upper Cretaceous Paleogeographic Evolution and Sequencestratigraphic framework of the Northwest Gulf of Mexico Rim, p. 45-82. In C. Bartolini, R. T. Buffler, and A. CantúChapa, eds. The Western Gulf of Mexico Basin – Tectonics, Sedimentary Basins, and Petroleum Systems. American Association of Petroleum Geologists, Memoir, 75.

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Imlay, R. W. 1936. Evolution of the Coahuila Peninsula, Mexico, part IV, geology of the western part of the Sierra de Parras: Geological Society of America Bulletin 47, 1091–1152. Massare, J. A., E. A. Buchholz, J. M. Kenney, and A.-M. Chomat. 2006. Vertebral morphology of Ophthalmosaurus natans (Reptilia: Ichthyosauria) from the Jurassic Sundance Formation of Wyoming. Paludicola 5(4):242-254. McGowan, C. and R. Motani. 2003. Handbook of Paleoherpetology, Part 8, Ichthyopterygia. Pfeil Verlag, München, 175 p. Motani, R. 1999. Phylogeny of the Ichthyopterygia. Journal of Vertabrate Paleontology 19:472495.

ROCHESTER INSTITUTE OF VERTEBRATE PALEONTOLOGY The Rochester Institute of Vertebrate Paleontology (RIVP) was founded in December of 1992 as a nonprofit corporation for the purpose of furthering scientific research in Vertebrate Paleontology. Officers President: William W. Korth Provost: Judy A. Massare

Research Associates Jon A. Baskin Department of Biological and Health Sciences, Texas A&M University-Kingsville. Kingsville, TX 78363 Jeffrey Chiarenzelli Department of Geology St. Lawrence University 23 Romoda Drive Canton, NY 13617 Robert L. Evander Department of Vertebrate Paleontology American Museum of Natural History Central Park West at 79th St. New York, NY 10024 Margaret Diamond 5215 Ledge Lane Williamsville, NY 14221

Board of Directors William W. Korth, Rochester, NY Judy A. Massare, Rochester, NY George McIntosh, Rochester, NY

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CONTENTS Rodents from the Chadronian (latest Eocene) Medicine Pole Hills local fauna, North Dakota. Part 1. Eutypomyidae, Cylindrodontidae and Pipestoneomys ALLEN J. KIHM Herpetofauna of the late Miocene Sappa Creek fauna, northwestern Kansas J. ALAN HOLMAN, LESLIE P. FAY, AND WILLIAM W. KORTH Large ichthyosaurian remains from the La Casita type locality (Tithonian, Upper Jurassic), Coahuila, Mexico MARIE-CÉLINE BUCHY AND ANABEL COVARRUBIAS CERVANTES

75-90 91-99

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