Diversidade, evolução e biogeografia dos Crocodylomorpha da América do Sul e África durante o Mesozóico

Crocodiles comprise a group of 23 living archosaur species, ranging from medium to large size and distributed around the intertropical area of the globe. They live in all continents, except for Antarctica and Europe. South America shows the greatest relative diversity, with eight species of four genera: Caiman, Melanosuchus, Paleosuchus and Crocodylus. Extant crocodiles have semi-aquatic life style, and can be found in shores, swamps and rivers. These animals are grouped within the monophyletic clade named Crocodylia, informally known as crocodilians. However, the extant diversity is only a fraction of the variety of species, life styles, habitats, size and morphology, that these animals have shown throughout their geological history. In fact, crocodilians are only a branch of a larger monophyletic group called Crocodylomorpha. The history of this clade begins 225 million years ago, between Middle Triassic (Ladinian) and Late Triassic (Carman). Much of this history, including the origin and diversification of many stoups and also of Crocodylomorpha itself, took part in lands that today are the African and South American continents. By the beginning of the Middle to Late Cretaceous, these lands were a part of the Gondwana supercontinent known as Western Gondwana. A great part of die crocodylomorph history not only happened in this region, but it was also largely biased by its geological history. This historical perspective only became reliable after the availability of a great number of phylogenetic analyses that have shown the close relationship between African and South American species, and also the affinities of these species with those from other gondwanic regions (Malagasy, Indian or Australian). These analyses began with the work of Benton & Clark (1988) and they have been building up and refining ever since. The actual knowledge of the Western Gondwana biogeography, especially during the Cretaceous, is largely based on analysis of dinosaurs (mainly non-avian Saurischia) and basal mammal distribution. However, crocodylomorphs are also useful for biogeography studies. They are a diversified group with well preserved fossil record, wide geographical distribution and the knowledge on their phylogenetic relationships is growing. They were terrestrial animals, except for a few fully marine groups (Teleosauridae, Metriorhvnchidae [Thalattosuchia] and Dyrosauridae) and so their distribution pattern might be guided by geological events of regional and continental fragmentation. Crocodylomorphs (like the terrestrial Notosuchia and Peirosauridae) are today one of the best groups for the understanding the fragmentation pattern of Gondwana by the Late Cretaceous (e.g., Turner, 2004). The recent discovery of a highly diverse crocodylomorph fauna in Madagascar, which is very similar to that of South America, but less diversified, drew the attention of many biogeographers to these animals (Krause et alii, 2006). Even before those recent discoveries and the cladistic approach toward the group, crocodylomorphs were stated as an example of ancestral Transatlantic (or Afro-South American) faunas. Buffetaut & Taquet (1979) and Buffetaut (1981, 1985) wrote classic papers on the sharing of crocodylomorph faunas between both continents by the Early Cretaceous (namely: Araripesuchus Price, 1959 and Sarcosuchus Broin & Taquet, 1966). In this chapter we present a general view of the African and South American fossil crocodylomorphs. We intend to distinguish native groups (whose evolutionary history is linked to the geological history of the continent) from those that are migrants or widely distributed and are related to more complex scenarios. The analysis is based on the phylogenetic relationships of the Afro-South American groups, their distribution and age (especially minimum ages of the fossil record). Ecology and physiology are also taken into consideration in order to help elucidate distribution patterns and biogeographical mechanisms, like vicariance or dispersion. We also emphasize the role of the crocodylomorph fossil record on the construction of the knowledge of the age and fragmentation sequence of Gondwana.