Paramphibia: A New Class of Tetrapods

PARAMPHIBIA: A NEW CLASS OF TETRAPODS

Mark A. S. McMenamin

Meanma Press 2015

Published February 16, 2015

Meanma Press South Hadley, Massachusetts, USA ©2015 by Mark A. S. McMenamin All rights reserved.

McMenamin, Mark A. S. Paramphibia: A New Class of Tetrapods/Mark A. S. McMenamin ISBN 1-893882-20-9 ISBN13 978-1-893882-20-1

Printed in the United States of America c 10 9 8 7 6 5

DOI: 10.13140/2.1.2569.0401/1

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LIST OF ILLUSTRATIONS

Figure 1. Geological map showing the fossil locality for Permodiadonta oklahoma n. gen. n. sp. Figure 2. Permodiadonta oklahoma n. gen. n. sp., occlusal view of jaw. Figure 3. Permodiadonta oklahoma n. gen. n. sp. SEM micrograph of tooth. Figure 4. Permodiadonta oklahoma n. gen. n. sp. SEM micrograph of punctate tooth. Figure 5. Permodiadonta oklahoma n. gen. n. sp., grooved enamel at base of tooth, SEM image. Figure 6. Morphogenetic field lines running across the jaw of Permodiadonta oklahoma n. gen. n. sp. Figure 7. Cladogram showing the distinction between vertebrates with complex morphogenetic fields and those with simpler morphogenetic fields. Figure 8. Stethacanthus productus, a Carboniferous shark. Figure 9. Diagrammatic map of the field lines in Permodiadonta oklahoma n. gen. n. sp. Figure 10. Reconstruction of Permodiadonta oklahoma n. gen. n. sp. Figure 11. Permodiadonta oklahoma n. gen. n. sp., labeled sketches of jaw. Figure 12. Permodiadonta oklahoma n. gen. n. sp., stereo pair of lingual side of jaw. Figure 13. Permodiadonta oklahoma n. gen. n. sp., stereo pair of ventral side of jaw. Figure 14. Permodiadonta oklahoma n. gen. n. sp., SEM view of bulbous tooth connected to low mediodistal ridge.

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PREFACE

In midsummer 2014, an Oklahoma fossil collector encountered an enigmatic jaw fossil in Permian strata at a site west of Waurika. I was fortunate enough to obtain this specimen, and the collector kindly provided the following information about the fossil locality: [I]t is like a wonderland of Permian even if it is a very small site. Dimetrodon, Edaphosaurus, Trimerorhachis, Diadectes, and shark [occur there]. It was [possibly an ancient meander] loop in the river. There are thousands of parts, but really no whole animals . . . As far as I know there has never been [a fossil like this one] found . . . . which would mean that it is one of a kind . . . a [unique type of Permian] animal. This would be a very good study piece. This is one of a kind as far as I know from Waurika. The purpose of this book is to demonstrate that this fossil is indeed a very good study piece. One of the best. Mark McMenamin South Hadley, Massachusetts February 16, 2015

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INTRODUCTION

IN ADDITION to the traditional four classes of tetrapods, amphibians (Class Amphibia), reptiles (Class Reptilia), birds (Class Aves) and mammals (Class Mammalia), herein is introduced a new, fifth class of tetrapods—Class Paramphibia. Paramphibians are characterized by a unique morphogenetic field with field lines that diverge and converge in alternating bundles. Restricted to Lower Permian terrestrial strata of the Wellington-Garber Complex, paramphibians are known from a single species, Permodiadonta oklahoma n. gen. n. sp., from the Ryan Formation in Oklahoma, USA (Fig. 1). The fossil locality is west of the Waurika fossil site. Waurika is well known for its abundant, if typically disarticulated, Permian vertebrate fossils (Olsen 1967; Davis 2012).

Figure 1. Geologic map showing the fossil locality for Permodiadonta oklahoma n. gen. n. sp. Geologic map units are as shown. Modified from Geology of Oklahoma by T. Wayne Furr and Massoud Safavi. 5

The unique jaw and punctate tooth morphology of Permodiadonta shares an odd mix of characteristics with fish, amphibians and reptiles. This mixture of traits precludes placement of the new species into any of these well-known vertebrate groups. In addition to punctate teeth (unusual in a tetrapod), there is a particularly unusual feature seen in Permodiadonta's jaw—morphogenetic field lines that alternately converge and distend as they run across the edge of the jaw (as revealed by placement of the animal's dentition). Another way of saying this is that the zahnreihe Z-spacing (DeMar 1972) is rhythmically variable. This strange configuration of zahnreihen (considered here as a proxy for the animal's morphogenetic field) reflects a body form that is as unique for vertebrates as the twisted-spindle morphology of the strange Early Cambrian echinoderm Helicoplacus is for Phylum Echinodermata. Helicoplacoids are placed in their own class (Class Helicoplacoidea), thus the placement here of Permodiadonta in its own tetrapod class (Paramphibia) is amply justified by the available evidence.

ZAHNREIHEN

Almost all reptiles show rows of "replacement" teeth; these rows are called zahnreihen (DeMar 1972). The cause of rows of teeth in reptiles and other vertebrates is sufficiently puzzling in evolutionary and developmental ("evo-devo") terms to lead DeMar (1972, p 438) to lament that "mathematical studies of the organization of dentitions are not likely to fully reveal causes." McMenamin (2009) considered zahnreihen to be expressions of morphogenetic fields that control the morphology of parazoan and metazoan body plans. DeMar (1972, p. 438) takes pains to disavow the possibility that a morphogenetic field might in some way cause zahnreihen tooth rows: "Zahnreihen . . . are probably not fundamental in a causational sense . . . [they] are without causal reality . . . [and are] unreal in a causational sense."

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It seems sensible to infer that the presence of a morphogenetic field can strongly influence development and morphological change. Here we will consider assigning a causal function to morphogenetic fields in terms of their influence on body form. Morphogenetic fields (or progenitor fields; Davidson 1993) can be traced back to an initiation at the fertilization event, namely the organization of maternal RNAs over the surface of the fertilized egg cell membrane. Once we begin to observe and interpret this aspect of biological reality, namely, that there is ontogenetic information contained in membrane patterns (Wells 2014), we can begin to appreciate that there are other influences on the morphology of creatures beyond the nuclear DNA. Not only will a proper understanding of morphogenetic fields and zahnreihen provide us with new tools to understand both the genesis of body form and macroevolutionary change, it will also help us to understand the relationship between odd changes to the morphogenetic field and the appearance of new higher taxa such as Class Paramphibia. It will also help us to reject false concepts of evolutionary gradualism and associated misunderstandings of macroevolution (McMenamin 2009, 2013). During the beginning of what might be called the 'punctuated equilibrium era' in paleontology, DeMar (1972, pp. 447-448) made reference to cracks in the edifice of evolutionary gradualism: "If it [be] necessary to invoke evolutionary gradualism, then it would not be possible to evolve gradually to either of these [zahnreihen] spacings without passing through spacings that would cause [maladaptive] gaps in the tooth row." Ricqulès and Bolt (1983, p. 22) were later to add, in their analysis of the puzzling nature of zahnreihen as applied to jaw morphology: "We would emphasize . . . that this descriptive usefulness of zahnreihen does not imply a particular ontogenetic and/or functional mechanism. Elucidation of such mechanisms is a separate problem." The time has arrived to deal with the mechanism problem. Paramphibians show us that zahnreihen are far more than merely successive rows of replacement teeth. This point is underscored by the enigmatic Triassic tetrapod Xenodiphyodon petraios Suess and Olsen, 1993, where we see the six anterior monocuspid teeth responding to a primary zahnreihe that runs roughly parallel to the jaw, and the tricuspid, molarized three posterior teeth responding to zahnreihen that run at nearly right angles to

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the primary zahnreihe. This unique and curious configuration shows that Xenodiphyodon (its group elevated below to the family Xenodiphyodonidae) has multiple zahnreihen running across the surface of its jaws. Zahnreihen are not merely parallel lines but form a sheetlike network where the lines appear, in Xenodiphyodon, to form an orthogonal grid. This analysis can be taken a step further. The morphogenetic fields of Cambrian archeocyaths can be considered as a three-dimensional network. The dimensionality of the archeocyathan "zahnreihen" equivalents may help to define the phylum-level assignment for this enigmatic group, so characteristic for the Cambrian Explosion (McMenamin 2009). Archeocyaths underscore the fact that the Cambrian Explosion, with its explosively sudden appearance of numerous animal phyla, is posing serious challenges for evolutionary biology and the paleontological sciences. Conventional darwinian explanations are in serious trouble. Of course, not all patterning in organisms may be attributed to zahnreihen. Divaricate patterns in mollusk shells are nicely described by stochastic fluctuation in pigment precursor concentrations along the growing edge of a shell (Seilacher 1972, his Fig 18). Pigment patterns in the zebra fish Danio rerio indicate that thyroid hormone plays an important role in pigment cell patterning (McMenamin et al. 2014). Androgens are thought to cause the secondary appearance of conical teeth on the premaxillary of male plethodontid salamanders (Ehmcke and Clemen 2000), a case demonstrating hormonal influence on the extent of the dental scleritome in amphibians. Finally, Gould and Katz (1975) described the geometrical constraints governing the growth of receptaculitids and the relationship of their growth pattern to the Fibonacci Sequence. None of these patterning types, however, can explain the odd emplacement of zahnreihen in the vertebrate jaw. Insurmountable difficulties will attend any attempt to explain the diverging and converging zahnreihen in Permodiadonta by means of, say, diffusing morphogen compounds. Any such morphogen concentration gradients would have to be so complexly structured that they would resemble, well, a morphogenetic field. The combination of converging/diverging zahnreihen and dyadic (fused) domal teeth in Permodiadonta directly contradicts the hypothesis of tooth patterning due to inhibitory chemical signals preventing tooth initiation ("zone of inhibition" [ZOI] theory) 8

that Whitlock and Richman (2013) present as an alternative to zahnreihen theory. The tooth patterning in vertebrates in many cases seems to represent response to an ur-toroidal (McMenamin 2009) morphogenetic grid system residing at or near the surface of the organism. The especially complex nature of the morphogenetic field in Permodiadonta is the primary justification for assigning this group to a new tetrapod class.

PARAMPHIBIA

This section will outline the reasons for defining the new Class Paramphibia. Comparisons with other tetrapod groups, particularly with regard to homologous and/or analogous traits, will be the focus of discussion here. The primary reason for creation of this new group of high taxonomic rank has to do with an emerging recognition of the importance of morphogenetic field analysis to questions of macroevolution. As mentioned above, this new approach is being developed out of necessity in an effort to advance our understanding of the seemingly intractable scientific conundrum of the Cambrian Explosion (McMenamin 2009, 2013).

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Figure 2. Permodiadonta oklahoma n. gen. n. sp. , occlusal view of jaw, labial side to right, lingual side to left. The labial curve of the jaw follows an emarginated cheek. Length of jaw 16 mm.

Permodiadonta oklahoma n. gen. n. sp. shows a unique combination of traits characteristic for the Paramphibia as defined here. The first of these has to do with the overall shape of the skull. The labial side of the jaw, occlusal view (Fig. 2), is deeply embayed, indicative of an emarginated cheek. This is the reflection of a posterior expansion of the skull, a trait shared with procolophonid parareptiles (McDonald 1991; Sues et al. 2000) such as Hypsognathus. Microsaurs such as Pantylus share a similar posteriorward expansion in skull morphology (Cope 1882; Romer 1969), and we may

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speak of convergent evolution in such cases (Kelley and Motani 2015). Functionally at least, the coronoid plate in Pantylus has developed into a grinding surface attached to a robust dentary (Williston 1925, his Figs. 6 and 18), comparable to similar morphology in Permodiadonta. These resemblances, however, are considered here to be superficial and due to homoplasy. Herrera and Pellmyr (2002, p. 64) note that "posterior expansion of the skull for the accommodation of extensive musculature for jaw closure in the processing [of] plant material . . . along with modification of molariform teeth into transversely expanded grinding or crushing surfaces" is indicative of herbivory in tetrapods, and indeed Permodiadonta oklahoma n. gen. n. sp. shows traits indicative of a plant diet. As part of the Permian land biota, quite a variety tetrapods developed modifications for a vegetarian lifestyle (Sues and Reisz 1998), including amphibians (Diadectes), parareptiles (procolophonids), synapsids (Edaphosaurus, caseids, etc.), the anapsids (pareiasaurs) and the reptiloid captorhinids (Labidosarus). The teeth of Permodiadonta oklahoma n. gen. n. sp. are well suited to a plant diet (Figs. 2-3). Its teeth are blunt with rounded to bulbous crowns suitable for masticating relatively soft plant material.

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Figure 3. Permodiadonta oklahoma n. gen. n. sp. , scanning electron micrograph (SEM) of tooth. Note the punctate tooth surface. Scale bar = 1 mm.

The odd combinations of traits in Permodiadonta may be described as follows. The animal shows a weird combination of rudimentary dental aveoli (tooth sockets), alveolar ridges and acrodontoid teeth, a character mix not usual in fish, amphibians or reptiles. Permodiadonta's teeth have foramina pits on tooth surfaces (Figs. 3-4), a character seen in some fish (e. g., pycnodonts) and microsaur amphibians (Hylerpeton; Carroll and Gaskill 1978, p. 74), but not to my knowledge in reptiles.

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Figure 4. Permodiadonta oklahoma n. gen. n. sp., scanning electron microscopy (SEM) image of tooth, enlargement showing foramina pitting (punctae). Scale bar = 300 microns.

Molarization is present in Permodiadonta, and in the Permian this is also observed in amphibians, reptiles and parareptiles. The deep lower jaw in Permodiadonta also occurs in Permian fish, amphibians, reptiles and parareptiles. Permodiadonta shares with reptiles and certain advanced amphibians (Diadectes; Williston 1925, his Fig. 17) a spacious Mecklian channel. The dorsal and ventral edges of the jaw ramus cross over in plan view (due to the emarginated cheek); this is also seen in the modern tuatara Sphenodon. "Jaw teeth" along the alveolar ridge formed by projections of the jaw occur

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in Permodiadonta and also occur in sphenodontids; compare these with those of a 'beaded' sphenodontian from the Cretaceous of Central México (Reynoso 1997). The acrodontoid teeth in Permodiadonta seemed to be fused to a labial parapet that is similar to that seen in sphenodontids. Extant sphenodontids have lost the teeth entirely and now only the bony projections remain to serve as pseudo-teeth. Emarginated cheeks can occur in reptiles other than Sphenodon and also in amphibians. Grooved enamel occurring at the base of teeth is a feature characteristic of parareptiles (Davis 2013, p. 181), and Permodiadonta shows this feature faintly on one of its teeth as seen in SEM view (Fig. 5).

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Figure 5. Permodiadonta oklahoma n. gen. n. sp. , scanning electron microscopy (SEM) image of tooth showing faint grooves in enamel at base of tooth. Scale bar = 0.5 mm.

Permodiadonta, however, does not appear to be a parareptile or procolophonid because if it was one, it would be among the earliest known (note that a Carboniferous parareptile with sharp teeth has just been reported; Modesto et al. 2015). All of the early members of these groups show pointed teeth indicative of insectivory. Permodiadonta has rudimentary teeth in an apparently less-derived evolutionary grade. They are clearly suited for crushing and/or mastication, and do not seem to be derived from sharply-pointed insectivore teeth. We may infer from this that paramphibians developed herbivory close to or at the time of emergence of their clade. Indeed, a plant-chewing trophic strategy may ultimately prove to be a defining characteristic for Class Paramphibia. Paramphibians may have been precocious plant feeders, perhaps even the first tetrapods to acquire the herbivorous lifestyle. Other detailed comparisons are possible between Permodiadonta and microsaur amphibians. Permodiadonta has a coronoid plate and ropy sculpturing on the dentary comparable to (but fainter than) that seen on Pantylus. Recall the fine pitting on the surfaces of teeth comparable to that of Hylerpeton. Comparisons may also be made between paramphibians and the procolophonid parareptiles. Ropy sculpturing on the dentary (Säilä 2010) is know to occur on Leptopleuron. There is a dentary foramen in Permodiadonta as in Lasasaurus (Falconnet et al. 2012). Interestingly, there are also ropy mediodistal ridges linking the teeth in Permodiadonta as in Lasasaurus (Falconnet et al. 2012). The cross section of the tooth in Permodiadonta is very similar to that in Spondylolestes (Cisneros 2008, his Fig. 7E). The symphaseal facet in Permodiadonta (although broken) is long as in Leptopleuron (Säilä 2010, her Figs. 4C-D). The labial side of the jaw appears to be a massive dentary as in Leptopleuron (Säilä 2010, her Figs. 4E). This trait is also occurs in Pantylus and Diadectes.

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The jaw in Permodiadonta has a sphenodontid-like labial parapet and a Mecklian channel that is comparable to that of Leptopleuron (Säilä 2010). The teeth are bulbous and molariform as in Haligona, and some teeth are organized into dyad molariforms as in Soternia, Leptopleuron and also Diadectes (Cabreira and Cisneros 2009; Säilä 2010). Permodiadonta oklahoma n. gen. n. sp. has a deep dentary giving it the appearance of a dicynodont-like jaw in miniature. This morphology is well-suited for consuming plant material. Finally, there may be effectively tricuspid teeth in Permodiadonta; tricuspids also occur in the Xenodiphyodonidae. We see then with Permodiadonta an odd mixture of traits shared rather evenly with unrelated groups of Permian vertebrates, but no key characters that allow Permodiadonta to be unambiguously placed into any of these groups. This by itself of course is no justification for erecting a new higher taxon of class rank. Like Xenodiphyodon, Permodiadonta would just be one among many tetrapod fossils of uncertain taxonomic affinity. However, there is an even more curious aspect of the Permodiadonta jaw relating to its morphogenetic field that is indicative of higher taxonomic rank for the Paramphibia. Let's explore this feature in the next section.

THE THIRD LAW OF MORPHOGENETIC EVOLUTION

Fig. 6 shows a plot of morphogenetic field lines running across the jaw of Permodiadonta oklahoma n. gen. n. sp. as determined by elongation of the major axes of the ellipsoids that are formed by its domal teeth as seen in plan view, and also by linear alignment in the foramina pit rows on tooth surfaces. Going from the anterior tip of the jaw in a posterior direction, observe how the field lines first converge, then diverge, then converge again, and finally diverge. This is a unique and unusual configuration that is unknown in any other type of tetrapod. It is this feature that provides justification for establishing here the new tetrapod Class Paramphibia.

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Figure 6. Morphogenetic field lines running across the jaw of Permodiadonta oklahoma n. gen. n. sp. Labial side to left. Note how the field lines do not run parallel but rather diverge and converge to form alternating bundles.

This new concept of Paramphibia has great utility because it divides all vertebrates into two groups, as can be seen in the cladogram shown in Fig. 7. The "lower" vertebrates (fishes, Paramphibians) are characterized by geometrically complex ("unruly") morphogenetic fields, whereas the "higher" vertebrates (higher on the cladogram, in any case; amphibians, reptiles, birds [including non-avian dinosaurs], and mammals) are characterized by simpler and more regular morphogenetic fields.

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Figure 7. Cladogram showing the distinction between vertebrates with complex morphogenetic fields and those with simpler morphogenetic fields. Ironically, more complex morphogenetic fields are associated with more "primitive" vertebrate types. (*) = Birds here include the non-avian dinosaurs.

Several examples will serve to illuminate this distinction between vertebrates with complex morphogenetic fields and those with simpler morphogenetic fields. Curiously, the more complex morphogenetic field types are associated with the supposedly more primitive vertebrate types. Among the cartilaginous fishes, consider the weird Carboniferous shark Stethacanthus (Fig. 8). Anterior emphasis of the scleritome gives the usual arrays of shark dentition, but in addition there is a patch of enlarged sclerites

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covering the head and furthermore, an extremely odd, large sclerite-covered flat dorsal fin that has been described as an ironing board or an anvil. It seems safe to infer that in Stethacanthus, its morphogenetic field is behaving in an unusual fashion. A sweeping geyser of morphogenetic field lines must be associated with the dorsal fin in Stethacanthus.

Figure 8. Stethacanthus productus, a Carboniferous shark with a very odd dorsal fin. Note the enlarged sclerites on the top of the head and on the bizarre dorsal fin, which bears a pad of large sclerites. A sweeping geyser of morphogenetic field lines are inferred here to be associated with the dorsal fin in Stethacanthus. Note cannibal feeding. Reconstruction by Dmitry Bogdanov.

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Judging by both scales and fin rays, the morphogenetic field in the vicinity of the tail of the modern coelacanth (Latimeria chalumnae) splays out in a narrow, diverging fountain of field lines, a sort of narrow, posterior version of the Stethacanthus dorsal fin anomaly. The odd field distortion of flatfishes (Platyichthus and related genera of the Order Pleuronectiformes) is another strange morphogenetic field perturbation seen in fish. And the molas or the ocean sunfishes of the family Molidae (they have the fewest vertebral segments of all the fishes!) bear one of the oddest morphogenetic fields in all of Phylum Chordata, so much so that it has become a classic image in D'Arcy Thompson's "morphing of fishes" (in On Growth and Form; Arthur 2006), where the posterior field lines splay out in an outrageous fashion, providing a marvelous explanation for the bizarre body plan of Mola mola. Surely the very strange tooth whorls of Helicoprion and Edestus (now assigned to the holocephalid fishes) represent a unique dental morphology without parallel in tetrapods. Finally, consider the bizarre disparity in the collection of sclerite types in the conodont apparatus; again this is an indication of complex morphogenetic field influence in the head region of these early chordate. In a meditation on D'Arcy Thompson's work, we again hear complaints (Arthur 2006) about lack of adequate "causal explanation," along with an agonized appeal to comparative developmental genetics. But the DNA-blueprint concept never seems to provide the answer. Higher vertebrates can of course show various tweaks to their morphogenetic fields, such as snouts, horns, tusks and flippers (the morphology of ichthyosaur flippers comes to mind here [in comparison to, say, cetacean flippers] as an example of both the first and second laws of morphogenetic evolution; McMenamin 2009), but rarely (with the possible exception of cetaceans, which may represent a heterochrony/neoteny-fueled special situation) is there ever the kind of extreme topological perturbation of the morphogenetic field as seen in fishes, and, as we will soon discuss, paramphibians. The second law of morphogenetic evolution states that "evidence for control by morphogenetic fields is most apparent in the earliest representatives of any particular lineage of complex life" (McMenamin 2009). To this we may now add the third law of morphogenetic evolution:

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HIGHER EVOLUTIONARY GRADES OF COMPLEX LIFE ARE CHARACTERIZED BY SIMPLIFICATION OF, OR STANDARDIZATION OF, THEIR RESPECTIVE MORPHOGENETIC FIELDS.

In a certain sense the third law is corollary to the second law. For example, a standardized morphogenetic field is going to be relatively less visible and less obviously in control of the morphology of an individual organism. In Stethacanthus morphogenetic field line anomalies are rather obvious, and they are even more obvious in the conodont apparatus. Such perturbations becomes less obvious in a paramphibian such as Permodiadonta, and downright subtle (but nevertheless important for species-level taxonomy) in a mammal such as Homo tsaichangensis McMenamin, 2015. There are several interesting Permian violations to the third law of morphogenetic evolution. The large Permian pelycosaur synapids Dimetrodon and Edaphosaurus are well-known for their sails, formed by vertebral neural spines that project upward to form a sail. Arguments attributing the impressive sails of these creatures to a thermoregulatory function are not convincing. Much more plausible is the likelihood that synapsid sails are the result of sexual selection. This leads to the fourth law of morphogenetic evolution:

SEXUAL SELECTION CAN GENERATE PROMINENT EXCEPTIONS TO THE OTHER LAWS OF MORPHOGENETIC EVOLUTION.

An additional example can show the applicability of the fourth law of morphogenetic evolution. The sail-backed pelycosaurs are perhaps the iconic Permian reptiles; much less well known is the curious Permian amphibian Platyhystrix. This amphibian, in spite of its relatively small size (40 cm long) in comparison to the synapsids, has a sail that is oddly similar to those of Dimetrodon and Edaphosaurus. The long neural spines in Platyhystrix expand upwards in the same way as do the anterior neural spines of Edaphosaurus

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pogonias. This is a high degree of similarity in unrelated animals, so we must be seeing here a comparable interaction in the small animal and in the larger animals between the urgings of sexual selection and the integrity of a simple or relatively fixed morphorgenetic field. Sexual selection is interesting in evolutionary terms. It seems to evince the power for morphological change that conventional darwinists would habitually attribute to "ordinary" natural selection. But sexual selection is not ordinary natural selection, it is more like a "natural-artificial" selection that so tightly closes the loop to differential reproductive success that it can effectively cause distension or hernia in the structured morphogenetic field, causing weird morphologies to pop up. The facial morphology of Triceratops horridus comes immediately to mind. It is important to emphasize that these weird morphologies are effectively superficial with regard to the creature's fundamental body plan. For example, the body plan of Dimetrodon is not fundamentally changed by its sail; its body plan is otherwise quite similar to the related, sail-less pelycosaur synapsid predators such as Varanodon and Varanosaurus. How can sails can appear in both reptiles and amphibians during the Permian? The neural spines in Dimetrodon are rectangular in cross section near their bases but develop a figure-eight cross section higher up the spine. This is usually interpreted as a strengthening adaptation, but a better interpretation is that it represents a split in the morphogenetic field lines as they diverge moving upwards and away from the midline. The morphogenetic field's influence in the sail is particularly evident in Edaphosaurus, where the elongate neural spines have cross-bars that make the spines resemble masts of a clipper ship with the sails furled. The even spacing and strange rib-like downward curvature of the cross pieces (like a melting yardarm) in Edaphosaurus pogonias trace out morphogenetic field lines wrapping downwards toward the main trunk of the animal, a continuation as it were of the field line response noted above in Dimetrodon's sail. Inhibitory morphogens do not explain the pattern. The sail then is, in a sense, a bubble or hernia in the morphogenetic field induced by the potent influence of sexual selection. Fishes of course can also be subject to sexual selection, but as is the case for Mola mola, their potential for fundamentally weird morphology is greater than is that of the 22

tetrapods. Stethacanthus shows a greater degree of perturbation of its morphogenetic field than does a fin-backed tetrapod, as an anvil is more topologically complex than a sail. Figure 9 shows an inferred map of the morphogenetic field lines in the paramphibian Permodiadonta. Like a maiden's wavy hair before she brushes it out, the field lines diverge and converge in bundles to form a wavy pattern of field lines that apply to the entire paramphibian body plan. The odd nature of the field lines become manifest, and can be studied, as they run across the jaw and influence the sclerite formation that represents Permodiadonta dentition. The jaw region in vertebrates can therefore be seen as a region where the character of the morphogenetic field becomes manifest, and this is precisely why this region of the body was confusing paleontologists as they struggled to understand the meaning of zahnreihen. It also explains the reason for assigning new class status rather than stem group status to the Paramphibia; the distinction is by virtue of a uniquely complex and derived morphogenetic field. The paramphibian morphogenetic field, as shown in Fig. 9 looking something like a psychedelic watermelon, is a derived state indicative of higher taxonomic rank for the group. It may be possible to fruitfully speculate on how the Paramphibian morphogenetic field acquired its peculiar configuration. Could the wavy longitudinal field lines be the result of some sort of contraction in a deuterostome's body axis pole separation without corresponding shortening of the longitudinal field lines? It is almost as if an eel-shaped animal underwent body axis shortening, but with the recalcitrant longitudinal field lines refusing to cooperate with a reduction in length. Latitudinal field lines would not be much affected in any case. Paramphibians therefore provide the evidence required to show that yes, manipulations of morphogenetic fields can indeed lead to the appearance of new higher taxa. This is a hugely important theoretical result that gives us an enormous boost in our efforts to understand how modifications of morphogenetic fields could lead to rapid macroevolutionary change, such as the otherwise enigmatic appearance of most eumetazoan animal phyla at the base of the Cambrian.

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Figure 9. Hypothetical map of the field lines in Permodiadonta oklahoma n. gen. n. sp. Its diagrammatic toroidal body plan is shown in side view; the dashed lines represent the alimentary canal or gut. The mouth opening is to the left.

Figure 10 shows a reconstruction of Permodiadonta oklahoma n. gen. n. sp. It has a generalized Permian tetrapod body form, with alternating variations in scale size to denote pulsating variations in the spacing of the morphogenetic field lines as extrapolated from detailed analysis of the mandible ramus.

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Figure 10. Reconstruction of Permodiadonta oklahoma n. gen. n. sp. Note the height of the lower jaw, a thickness appropriate for a herbivorous paramphibian. Note also the variation in scale size across the length of the body, an expression of wavy morphogenetic field lines in Permodiadonta. This surface texturing is conjectural but quite in accord with the inferences made here regarding the complex paramphibian morphogenetic field. Length of animal approximately 17 cm.

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SYSTEMATIC PALEONTOLOGY

Kingdom Animalia Phylum Chordata Superclass Tetrapoda Class Paramphibia nov. Description. As per the species. Age and Distribution. Early Permian of North America. Paramphibia may have been a victim of the Permo-Triassic mass extinction.

Order Permodiadontia nov. Description. As per the species.

Family Permodiadontidae nov. Description. As per the species.

Genus Permodiadonta n. gen. Description. As per the species.

Permodiadonta oklahoma n. gen. n. sp. (Figs. 2-6, 10-14)

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Type specimen. 1 of 1/19/2015; NCSM 28323. Diagnosis. Lower mandible of cellular bone with teeth developed on a low labial parapet and adjacent coronoid plate. Relatively wide interdental regions. Labial view of jaw ramus dominated by deep dentary (Figs. 11A-C, 12, 13). In occlusal view, molarized tooth rows run across the jaw at alternating oblique angles (Fig. 6). A low labial parapet runs along the edge of the jaw, hosting acrodontoid teeth at the jaw margin. Teeth on the coronoid plate show alveolar root-like anchorages, although sockets or alveoli are not obvious. Fractured transverse section through one tooth shows a concentric pattern suggestive of a central canal with circular cross section. Vertical fractures show marrow-like pockets (Fig. 12) and irregular canal-like zones embedded in enameloid material. An external mandibular foramen is visible on the posterior part of the jaw. In lingual view (Fig. 11B), the coronoid plate forms a narrow shelf or roof over a spacious Mecklian channel. The tip of the jaw is broken but the symphyseal region appears to widen out to a roughly rhombohedral facet. A nearly horizontal groove with marbled bone and enameloid material occurs in the symphyseal region; whether or not this represents the alveolus of a tusk-like tooth is unknown. The splenial is narrow and forms a ventral keel on the mandible; the surangular is immediately above the articular (Fig. 11A, 13). Faint sculpturing is visible on the dentary. Teeth are bulbous to domal-shaped and in many cases punctate, bearing fine foramina pits (Figs. 2-4, 14). The punctae may show faint alignment in rows parallel to the long axes of the ellipsoidal teeth. Teeth are typically linked either by molarized dyadic fusions or by low mediodistal ridges (Fig. 14).

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Figure 11. Permodiadonta oklahoma n. gen. n. sp. A, lingual view of jaw, anterior to right; B, labial view of jaw, anterior to left; C, ventral view of jaw. Abbreviations: art, articular; c, coronoid plate; d, dentary; emf, external mandibular foramen; m, Mecklian channel; s, splenial; sa, surangular. Length of jaw 16 mm.

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Figure 12. Permodiadonta oklahoma n. gen. n. sp., slightly oblique stereo pair of lingual side of jaw. Length of jaw 16 mm.

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Figure 13. Permodiadonta oklahoma n. gen. n. sp., slightly oblique stereo pair of ventral side of jaw showing ventral keel formed by the splenial. Length of jaw 16 mm.

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Figure 14. Permodiadonta oklahoma n. gen. n. sp., SEM view of bulbous tooth connected to low mediodistal ridge in the lower central part of the photomicrograph. Scale bar = 500 microns.

Remarks. The fusions or low mediodistal ridges linking the teeth (Falconnet et al. 2012) are comparable to those inferred from a cast for the procolophonid parareptile Lasasaurus; however, in Permodiadonta the enameloid ridges are more like thick draping sheets than ropy ridges, and they are best developed near the labial parapet. In Lasasaurus, "the kind of tooth implantation is hard to identify" (Falconnet et al. 2012, p. 361) because the relationship between the mediodistal ridges (which seem to reflect cellular bone structure) and tooth ankylosis is unclear. Dental pitting is known from the

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microsaur Hylerpeton, however, the teeth of Permodiadonta are not pointed and the symphyseal suture does not appear to be triangular as in Hylerpeton (Carroll and Gaskin 1978). The punctate Permodiadonta teeth are striking. The pattern imparts to the domal surface of the tooth a resemblance to the outer surface of the valve of a punctate brachiopod. The spacious Mecklian groove/channel of Permodiadonta is somewhat like that of the sphenodontian Sphenotitan Martinez et al., 2014. Faint possible sculpturing may be present on the lingual side of the splenial, somewhat resembling the jaw sculpturing (Romer 1969) as seen in the microsaur Pantylus. The splenial is narrow and forms a ventral ridge on the mandible, also as in Pantylus, but the inferred surangular and articular are one atop the other more like Dimetrodon than like Pantylus where they occur side to side. Permodiadonta therefore shows a strange mix of characteristics that are shared out fairly evenly among microsaurs, procolophonids, sphenodontids, and even pelycosaurs, and yet it appears that Permodiadonta does not belong to any of these groups. The Permodiadonta dentition seems well suited to processing high-fiber plant material. No unambiguous wear facets have been identified on Permodiadonta teeth; however, its largest tooth does have a surface texture on its upper surface suggestive of wear polish. It is possible that this small creature would have mostly fed upon softer and more delicate plant material, and this might explain the lack of obvious wear facets. Permodiadonta may have nevertheless hosted an endosymbiont gut microbiota to aid with the digestion of plant matter. The addition of this entirely new type of tetrapod herbivore to an already long list of Permian plant eaters (diadectomorphs, procolophonids, caseids, dicynodonts, edaphosaurids, pareiasaurs and captorhinids such as Labidosaurus) adds credence to Suess and Reisz's (1998) statement that "clades of herbivorous forms are typically much more diversified than their faunivorous sister taxa." Material. Partial mandible, left mandible ramus, weight 0.644 g. Age and Locality data. Early Permian, Ryan Formation; Wellington-Garber Complex, from a site west of Waurika, Oklahoma.

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Class ?Amphibia Order unknown Family Xenodiphyodonidae nov.

Description. Tetrapod with labiolingually compressed anterior teeth of the mandible, and tricuspid molars posterior to these (Sues and Olsen 1993). Morphogenetic field lines (longitudinal and latitudinal; McMenamin 2009) meet at right angles in the molars, with longitudinal line represented by the anterior tooth row and the latitudinal lines represented by the line of cusps in each tricuspid molar. Remarks. Sues and Olsen (1993) suggested a procolophonid parareptile affinity for Xenodiphyodon, however, the labiolingually compressed anterior teeth of the holotype (USNM 448631) closely resemble those of the gymnarthrid microsaurs Cardiocephalus and Bolterpeton (see Anderson and Reisz 2011). Therefore the Xenodipyodonidae are assigned here with question to the Amphibia. As such, in terms of evolutionary grade (this would be the case under the parareptile interpretation as well), they have crossed the transition from complex morphogenetic fields (Paramphibia) to simplified morphogenetic fields (Amphibia). This is nicely shown by the near exact orthogonal crossing of the field lines in the posterior portion of the type specimen jaw. Note that in the newly described, earliest (Carboniferous) parareptile, Erpetonyx arsenaultorum, the morphogenetic field influence has simplified to such an extent that we can see a rhythmic alternation in tooth length in a series of nine alternating long-short teeth (Modesto et al. 2015, their Fig. 2B). The Erpetonyx pattern is best explained by means of ZOI (zone of inhibition) theory. Whitlock and Richman (2013; b''' in their Fig. 3) show a zone of inhibition-generated rhythmic alternation of eight long-short teeth almost exactly as seen in Erpetonyx.

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ACKNOWLEDGEMENTS

I wish to thank Blanca Carbajal Gonzalez, D. L. Schulte McMenamin, S. K. McMenamin, S. Pivar, S. Rachootin, V. Schneider, P. Weaver and D. Smith for assistance with various aspects of this research. The type specimen resides at the North Carolina Museum of Natural Sciences (NCSM), Raleigh, North Carolina, USA.

BIBLIOGRAPHY

Anderson, J. S. and Reisz, R. R. 2011. A new microsaur (Tetrapoda: Leopspondyli) from the Lower Permian of Richards Spur (Fort Sill), Oklahoma. Canadian Journal of Earth Sciences, v. 40, n. 4, p. 499-505. Arthur, W. 2006. D'Arcy Thompson and the theory of transformations. Nature Reviews Genetics, v. 7, p. 401-406, doi:10.1038/nrg1835. Cabreira, S. F. and Cisneros, J. C. 2009. Tooth histology of the parareptile Soturnia caliodon from the Upper Triassic of Rio Grande do Sul, Brazil. Acta Palaeontological Polonica, v. 54, n. 4, p. 743-748. Carroll, R. L. and Gaskill, P. 1978. The Order Microsauria. Memoirs of the American Philosophical Society, v. 126, p. 1-211. Cope, E. D. 1882. Third contribution to the history of the Vertebrata of the Permian Formation of Texas. Proceedings of the American Philosophical Society, v. 20, p. 447-461. Cranston, P. S., F.-T. Krell, K. Walker and D. Hewes. 2015. Wiley's Early View constitutes valid publication for date-sensitive nomenclature. Systematic Entomology, v. 40, p. 2-4.

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Davidson, E. H. 1993. Later embryogenesis: regulatory circuitry in morphogenetic fields. Development, v. 118, p. 665-690. Davis, K. 2012. Lower Permian Vertebrates of Oklahoma. Volume 1—Waurika. www.ddfossils.com, 206 p. Davis, K. 2013. Lower Permian Vertebrates of Oklahoma. Volume 2—Richards Spur. www.ddfossils.com, 228 p. DeMar, R. 1972. Evolutionary implications of Zahnreihen. Evolution, v. 26, n. 3, p. 435-450. Ehmcke, J. and Clemen, G. 2000. Teeth and their sex-dependent dimorphic shape in three species of Costa Rican plethodontid salamanders (Amphibia: Urodela). Annals of Anatomy, v. 182, v. 5, p. 403-414. Falconnet, J., Andriamihaja, M., Läng, É. and Steyer, J.-S. 2012. First procolophonid (Reptilia, Parareptilia) from the Lower Triassic of Madagascar. Comptes Rendus Palevol, v. 11, p. 357-369. Gould, S. J. and Katz, M. 1975. Disruption of ideal geometry in the growth of receptaculitids: a natural experiment in theoretical morphology. Paleobiology, v. 1, p. 1-20. Herrera, C. M. and Pellmyr, O., eds. 2002. Plant-Animal Interactions: An Evolutionary Approach. Wiley, New York, 328 p. McDonald, N. G. 1991. Paleontology of the Early Mesozoic (Newark Supergroup) rocks of the Connecticut Valley. In Matson, L. R., ed., Field Trip Guidebook and Proceedings, National Association of Geology Teachers 1991 Annual Meeting, p. 89-108, Greenfield Community College, Greenfield, Massachusetts. McMenamin, M. A. S. 2009. Paleotorus: The Laws of Morphogenetic Evolution. South Hadley, Massachusetts. Meanma Press, South Hadley, Massachusetts. ISBN13 978-1-893882-188, ISBN10 1-893882-18-7. McMenamin, M. A. S. 2013. Breakthrough on the Cambrian Explosion. BioScience, v. 63, n. 10, p. 834-835.

35

McMenamin, M. A. S. 2015. Homo tsaichangensis and Gigantopithecus. Meanma Press, South Hadley, Massachusetts, 12 p. ISBN 1-893882-19-5, ISBN13 978-1-893882-19-5, doi:10.13140/2.1.3463.7121 McMenamin, S. K., Bain, E. J., McCann, A. E., Patterson, L. B., Eom, D. S., Waller, Z. P., Hamill, J. C., Kuhlman, J. A., Eisen, J. S. and Parihy, D. M. Tyroid hormone-dependent adult pigment cell lineage and pattern in zebrafish. Science, v. 345, n. 6202, doi:10.1126/science.1256251. Modesto, S. P., Scott, D. M., MacDougall, M. J., Sues, H.-D., Evans, D. C. and Reisz, R. R. 2015. The oldest parareptile and the early diversification of reptiles. Proceedings of the Royal Society B, v. 282, 20141912, http://dx.doi.org/10.1098/rspb.2014.1912. Olsen, E. C. 1967. Early Permian Vertebrates of Oklahoma. Oklahoma Geological Survey Circular 74. The University of Oklahoma, Norman, Oklahoma, 111 p. Reynoso, V. H. 1997. A 'beaded' sphenodontian (Diapsida: Leipidosauria) from the Early Cretaceous of Central Mexico. Journal of Vertebrate Paleontology, v. 17, p. 52-59. Ricqulès, A. de and Bolt, J. R. 1983. Jaw growth and tooth replacement in Captorhinus aguti (Reptilia: Captorhinomorpha): A morphological and histological analysis. Journal of Vertebrate Paleontology, v. 3, n. 1, p. 7-24. Romer, A. S. 1969. The cranial anatomy of the Permian amphibian Pantylus. Brevoria, v. 314, p. 1-37. Säilä, L. K. 2010. Osteology of Leptopleuron lacertinum Owen, a procolophonoid parareptile from the Upper Triassic of Scotland, with remarks on ontogeny, ecology and affinities. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, v. 101, p. 1-25. Seilacher, A. 1972. Divaricate patterns in pelecypod shells. Lethaia, v. 5, p. 325-343. Sues, H.-D. and Olsen, P. E. 1993. A new procolophonid and a new tetrapod of uncertain, possibly procolophonian affinities from the Upper Triassic of Virginia. Journal of Vertebrate Paleontology, v. 13, n. 3, p. 282-286.

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Sues, H.-D. and Reisz, R. R. 1998. Origins and early evolution of herbivory in tetrapods. Trends in Ecology and Evolution, v. 13, n. 4, p. 141-145. Sues, H.-D., Olsen, P. E., Scott, D. M. and Spencer, P. S. 2000. Cranial osteology of Hypsognathus fenneri, a latest Triassic procolophonid reptile from the Newark Supergroup of Eastern North America. Journal of Vertebrate Paleontology, v. 20, n. 2, p. 275-284. Wells, J. 2014. Membrane patterns carry ontogenetic information that is specified independently of DNA. BIO-Complexity, v. 2, p. 1-28, doi:10.5048/BIO-C.2014.2. Whitlock, J. A. and Richman, J. M. 2013. Biology of tooth replacement in amniotes. International Journal of Oral Science, v. 6, p. 66-70, doi:101038/ijos.2013.36. Williston, S. W. 1925. The Osteology of the Reptiles. Cambridge, Harvard University Press, 300 p.

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