Eogavialis Africanum

''Eogavialis'' is an extinct genus of eusuchian crocodylomorph, usually regarded as a gavialoid crocodylian. It superficially resembles ''Tomistoma schlegelii'', the extant false gharial, and consequently material from the genus was originally referred to ''Tomistoma''. Indeed, it was not until 1982 that the name ''Eogavialis'' was constructed after it was realised that the specimens were from a more basal form.

Species

The genus was first described by Charles William Andrews in 1901 when Andrews named a new species of ''Tomistoma'', ''T. africanum'', on the basis of a specimen found from an outcrop of the Qasr el-Sagha Formation in Egypt, about 20 miles northwest of Faiyum, dating back to the Priabonian stage of the late Eocene 37.2 to 33.9 million years ago. Other specimens were later found from the Gebel Qatrani Formation, slightly younger than the Qasr el-Sagha dating back to the Rupelian stage of the early Oligocene 33.9 to 28.4 million years ago, and near the locality where the original specimen of ''T. africanum'' was found in the Faiyum depression. A new species was also found from this locality and named ''T. gavialoides'' by Andrews in 1905.

One of the first papers to identify the differences between these two species and others within ''Tomistoma'' was published in 1955 by J. A. Kälin. Other papers were written in the following decades that also questioned these species' relationships within Tomistominae. Eric Buffetaut proposed the genus name ''Eogavialis'' in 1982 and reassigned both ''T. africanum'' and ''T. gavialoides'' to it.

A third species was assigned to ''Eogavialis'' in 2003 from material found in the 1990s from the lower Nawata Formation of the Turkana basin outcropping in Lothagam, Kenya. The strata from which the material was found dates back to the late Miocene and early Pliocene and nasal bones made contact with one another, a feature also seen in ''Tomistoma''. However, this characteristic has since been shown to be present in other extinct gavialids, meaning that premaxilla and nasal contact is a plesiomorphic trait of all tomistomines, including basal ones. ''Eogavialis'' also has a very similar cranial anatomy when compared to ''Tomistoma'', having the same proportions, rostral length, and tooth number, leading to the conclusion by some authors of papers published after 1982 that ''Eogavialis'' is synonymous with ''Tomistoma''.

Phylogeny

Tomistomines have been traditionally classified as crocodiles. However, molecular analyses of the false gharial, the only living tomistomine, suggest that the subfamily is actually within Gavialidae (along with the modern gharial of the subfamily Gavialinae) rather than Crocodylinae. The presence of a prominent crista that runs along the postorbital in ''Eogavialis'' testifies to its position as a gavialid. Other characteristics such as a rectangular skull table, subcircular orbits with everted orbital rims, and a constricted antorbital area are also shared with ''Eogavialis'' and other modern gavialids, as seen in a well preserved skull of ''E. africanum'' housed at Yale (YPM 6263) and material from Kenya of ''E. andrewsi''.

''Eogavialis'' has often been proposed to be non-tomistomine due to its lack of supposedly crocodylid synapomorphies needed in order for a taxon to be placed within Tomistominae. The genus lacks the exposure of the vomer on the palate that has been viewed as a characteristic of tomistomines. The trend for a long, narrow rostrum developing progressively over time as seen in ''Eogavialis'' has been used to suggest that the genus was a direct ancestor of ''Gavialis''. ''Gryposuchus'' was once seen as phylogenetically between ''Eogavialis'' and ''Gavialis''.

''Eogavialis africanum'' was included in the study on the phylogenetic relationships of putative fossil gavialoids published by Lee & Yates (2018). The authors considered it most likely that ''E. africanum'' was not a gavialoid, or even a crocodylian, but rather a member of the clade of non-crocodylian eusuchians that also included the genera ''Argochampsa'', '' Eosuchus'', ''Eothoracosaurus'' and ''Thoracosaurus''.

Paleoecology

''E. andrewsi'' was found in fluvial deposits within the Lower Nawata member of the Nawata Formation in Kenya. A broad, shallow, meandering river is thought to have existed at the time of deposition, suitable for an aquatic gavialid such as ''Eogavialis''. Evidence for a semideciduous tree savanna that may have surrounded the river is present in the lower beds, and a general trend in increased aridity can be seen in overlying beds in the member, suggesting a dry thornbush savanna environment. Fossils present from the strata that material from ''E. andrewsi'' were found include those of numerous teleost fish such as osteoglossiformes and perciformes, many turtles, crocodiles, and birds such as ostriches, the enigmatic large bird '' Eremopezus'', anatids, rails, and owls, as well as many mammals representing both living and extinct taxa common in Africa.

The area of the Gebel Qatrani Formation in the Faiyum Depression where most of the well-preserved specimens of ''E. africanum'' and ''E. gavialoides'' were found was also deposited in a fluvial paleoenvironment, although much older. Other fossils found from the formation include those of turtles, crocodiles, hyaenodontids, proboscideans such as '' Phiomia'', '' Palaeomastodon'', and '' Moeritherium'', the Embrithopodan '' Arsinoitherium'', numerous species of hyraxes, artiodactyls, as well as some of the earliest simian primates such as ''Apidium'', ''Catopithecus'', ''Oligopithecus'', and '' Aegyptopithecus''. Discoveries from this formation have added greatly to the understanding of mammalian evolution in Africa. The presence of this type of fauna suggests a humid, tropical climate existed in Egypt during the Oligocene.

Much of the Gebel Qatrani consists of other deposits that represent both marine and non-marine sedimentary depositional environments. Some specimens of ''Eogavialis'' are known from these strata as well, suggesting that the genus may also have been adapted to a coastal marine habitat. This differs from the mostly freshwater habitats inhabited by extant crocodilians.

References

{{Taxonbar, from=Q1882843, from2=Q40444878, from3=Q40444932, from4=Q40444992, from5=Q112922573

Neosuchians
Prehistoric pseudosuchian genera
Miocene reptiles of Africa
Eocene reptiles of Africa
Pliocene reptiles of Africa
Oligocene reptiles of Africa
Eocene crocodylomorphs
Miocene crocodylomorphs
Oligocene crocodylomorphs
Pliocene crocodylomorphs
Fossil taxa described in 1982
Taxa named by Éric Buffetaut