Eogavialis

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Eogavialis
Temporal range: Late Eocene – Pliocene, 37.2–2.59  Ma
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Pseudosuchia
Clade: Crocodylomorpha
Clade: Metasuchia
Clade: Neosuchia
Clade: Eusuchia
Genus:† Eogavialis
Buffetaut 1982
Species
  • †E. africanum(Andrews 1901 [originally Tomistoma africanum]) (type)
  • †E. andrewsi(Storrs 2003)
  • †E. gavialoides(Andrews 1905 [originally Tomistoma gavialoides])

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. [1]

Contents

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. [2] Other papers were written in the following decades that also questioned these species' relationships within Tomistominae. [3] [4] [5] 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. [6] The strata from which the material was found dates back to the late Miocene and early Pliocene, around 11.61 to 2.59 million years ago. This extends the fossil range of the genus by approximately 17 million years. It was named E. andrewsi for Charles Williams Andrews. [7] The holotype consists of a well preserved, nearly complete skull.

One reason why Eogavialis was initially placed within Tomistoma was due to the fact that the premaxilla 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. [8]

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. [9] 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, [10] [11] 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. [12] 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. [11]

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 . [13]

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 . [14] 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. [15] [16] [17] Some specimens of Eogavialis are known from these strata as well, [18] suggesting that the genus may also have been adapted to a coastal marine habitat. [19] This differs from the mostly freshwater habitats inhabited by extant crocodilians.

Related Research Articles

<span class="mw-page-title-main">Gavialidae</span> Family of gharial crocodylians

Gavialidae is a family of large semiaquatic crocodilians with elongated, narrow snouts. Gavialidae consists of two living species, the gharial and the false gharial, both occurring in Asia. Many extinct members are known from a broader range, including the recently extinct Hanyusuchus. Gavialids are generally regarded as lacking the jaw strength to capture the large mammalian prey favoured by crocodiles and alligators of similar size so their thin snout is best used to catch fish, however the false gharial has been found to have a generalist diet with mature adults preying upon larger vertebrates, such as ungulates.

<i>Tomistoma</i> Genus of crocodilians

Tomistoma is a genus of gavialid crocodilians. They are noted for their long narrow snouts used to catch fish, similar to the gharial. Tomistoma contains one extant (living) member, the false gharial, as well as potentially several extinct species: T. cairense, T. lusitanicumT. coppensi, and T. dowsoni. However, these species may need to be reclassified to different genera as studies have shown them to be paraphyletic, for example: previously assigned species T. taiwanicus from Taiwan, is reclassified to the genus Toyotamaphimeia, and T. dowsoni should be excluded from Tomistoma based on phylogenetic analysis.

<i>Toyotamaphimeia</i> Extinct genus of reptiles

Toyotamaphimeia is a genus of extinct gavialid crocodylian which lived in Japan and Taiwan during the Pleistocene. A specimen recovered in 1964 at Osaka University during the construction of a new science building has been dated to around 430–380 thousand years old based on the stratum in which it was found. Toyotamaphimeia was a fairly large crocodylian measuring approximately 6.3–7.3 metres (21–24 ft) long. Two species are named, T. machikanensis from Japan and T. taiwanica from Taiwan, both originally described as members of the genus Tomistoma.

<i>Gavialosuchus</i> Extinct genus of reptiles

Gavialosuchus is an extinct genus of gavialoid crocodylian from the early Miocene of Europe. Currently only one species is recognized, as a few other species of Gavialosuchus have since been reclassified to other genera.

<i>Harpacochampsa</i> Extinct genus of crocodilian

Harpacochampsa is a poorly known Early Miocene crocodilian from the Bullock Creek lagerstätte of the Northern Territory, Australia. The current specimen consists of a partial skull and fragments of a long, slender snout reminiscent of that of a false gharial, demonstrating that it was a piscivore in life.

Dollosuchoides, colloquially known as the Crocodile of Maransart, is an extinct monospecific genus of gavialoid crocodilian, traditionally regarded as a member of the subfamily Tomistominae. Fossils have been found in the Brussel Formation of Maransart, Belgium and date back to the middle Eocene.

<i>Eothoracosaurus</i> Extinct genus of reptiles

Eothoracosaurus is an extinct monospecific genus of eusuchian crocodylomorphs found in Eastern United States which existed during the Late Cretaceous period. Eothoracosaurus is considered to belong to an informally named clade called the "thoracosaurs", named after the closely related Thoracosaurus. Thoracosaurs in general were traditionally thought to be related to the modern false gharial, largely because the nasal bones contact the premaxillae, but phylogenetic work starting in the 1990s instead supported affinities within gavialoid exclusive of such forms. Even more recent phylogenetic studies suggest that thoracosaurs might instead be non-crocodilian eusuchians.

<i>Eosuchus</i> Extinct genus of reptiles

Eosuchus is an extinct genus of eusuchian crocodylomorph, traditionally regarded as a gavialoid crocodilian. It might have been among the most basal of all gavialoids, lying crownward of all other known members of the superfamily, including earlier putative members such as Thoracosaurus and Eothoracosaurus. Fossils have been found from France as well as eastern North America in Maryland, Virginia, and New Jersey. The strata from which specimens have been found date back to the late Paleocene and early Eocene epochs.

<i>Euthecodon</i> Extinct genus of crocodilian

Euthecodon is an extinct genus of long-snouted crocodile. It was common throughout much of Africa during the Neogene, with fossils being especially common in Kenya, Ethiopia, and Libya. Although superficially resembling that of gharials, the long snout was a trait developed independently from that of other crocodilians and suggests a diet of primarily fish. Euthecodon coexisted with a wide range of other crocodiles in the areas it inhabited before eventually going extinct during the Pleistocene.

<i>Gryposuchus</i> Extinct genus of gavialoid crocodilian

Gryposuchus is an extinct genus of gavialid crocodilian. Fossils have been found from Argentina, Colombia, Venezuela, Brazil and the Peruvian Amazon. The genus existed during the Miocene epoch. One recently described species, G. croizati, grew to an estimated length of 10 metres (33 ft). Gryposuchus is the type genus of the subfamily Gryposuchinae, although a 2018 study indicates that Gryposuchinae and Gryposuchus might be paraphyletic and rather an evolutionary grade towards the gharial.

<i>Kentisuchus</i> Extinct genus of reptiles

Kentisuchus is an extinct genus of gavialoid crocodylian, traditionally regarded as a member of the subfamily Tomistominae. Fossils have been found from England and France that date back to the early Eocene. The genus has also been recorded from Ukraine, but it unclear whether specimens from Ukraine are referable to Kentisuchus.

Maroccosuchus zennaroi is an extinct gavialoid crocodylian from the Early Eocene of Morocco, traditionally regarded as a member of the subfamily Tomistominae.

Paratomistoma is an extinct monospecific genus of gavialoid crocodylian. It is based on the holotype specimen CGM 42188, a partial posterior skull and lower jaw discovered at Wadi Hitan, Egypt, in Middle Eocene-age rocks of the Gehannam Formation. The skull is unfused but considered morphologically mature. Paratomistoma was named in 2000 by Christopher Brochu and Philip Gingerich; the type species is P. courti in honor of Nicholas Court, who found CGM 42188. They performed a phylogenetic analysis and found Paratomistoma to be a derived member of Tomistominae, related to the false gharial. It may have been a marine or coastal crocodilian.

Prodiplocynodon is an extinct genus of basal crocodyloid crocodylian. It is one of the only crocodyloids known from the Cretaceous and existed during the Maastrichtian stage. The only species of Prodiplocynodon is the type species P. langi from the Lance Formation of Wyoming, known only from a single holotype skull lacking the lower jaw.

Siquisiquesuchus is an extinct genus of gavialid crocodilian. It is known from cranial remains and a few postcranial bones found in Miocene-age rocks of the Castillo Formation in northwestern Venezuela.

<i>Penghusuchus</i> Extinct genus of reptiles

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<i>Thecachampsa</i> Extinct genus of reptiles

Thecachampsa is an extinct genus of gavialoid crocodylian, traditionally regarded as a member of the subfamily Tomistominae. Fossils have been found from the eastern United States in deposits of Miocene age. Those named in the 19th century were distinguished primarily by the shape of their teeth, and have since been combined with T. antiquus. More recently erected species were reassigned from other genera, although their assignment to Thecachampsa has since been questioned.

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<span class="mw-page-title-main">Gavialoidea</span> Superfamily of large reptiles

Gavialoidea is one of three superfamilies of crocodylians, the other two being Alligatoroidea and Crocodyloidea. Although many extinct species are known, only the gharial Gavialis gangeticus and the false gharial Tomistoma schlegelii are alive today, with Hanyusuchus having become extinct in the last few centuries.

Tomistoma cairense is an extinct species of gavialoid crocodilian from the Lutetian stage of the Eocene era. It lived in North East Africa, especially Egypt. Remains of T. cairense have been found in the Mokattam Formation, in Mokattam, Egypt. Tomistoma cairense did not have a Maxilla process within their lacrimal gland, whereas all extant (living) crocodilians do.

References

  1. ↑ Buffetaut, E. (1982). "Systématique, origine et évolution des Gavialidae Sud-Américains". Geobios. 15 (Suppl 1): 127–140. doi:10.1016/S0016-6995(82)80107-1.
  2. ↑ Kälin, J. (1955). "Crocodilia". In Piveteau, J. (ed.). Traité de Paléontology. Vol. 5. Paris: Masson. pp. 695–784.
  3. ↑ Langston, W. Jr. (1965). Fossil crocodilians from Columbia and the Cenozoic History History of the Crocodilia in South America. Publications in the Geological Sciences. Vol. 52. Los Angeles: University of California.
  4. ↑ Sill, W. D. (1970). "Nota preliminar sobre un nuevo gavial del Plioceno de Venezuela y unda discusión de los gaviales sudamericanos". Ameghiniana. 7: 151–159.
  5. ↑ Hecht, M. K.; Malone, B. (1972). "On the early history of the gavialid crocodilians". Herpetologica. 28 (3): 281–284. JSTOR   3890639.
  6. ↑ Leakey, M. G.; Feibel, C. S.; Bernor, R. L.; et al. (1996). "Lothagam: A record of faunal change in the Late Miocene of East Africa". Journal of Vertebrate Paleontology . 16 (3): 556–570. doi:10.1080/02724634.1996.10011339.
  7. ↑ Storrs, G. W. (2003). "Late Miocene-Early Pliocene crocodilian fauna of Lothagam, southwest Turkana Basin, Kenya". Lothagam: The Dawn of Humanity in Eastern Africa. New York: Columbia University Press. pp. 137–159. ISBN   0-231-11870-8.
  8. ↑ Tchernov, E. (1986). Evolution of the Crocodiles in East and North Africa. Cahiers de Paléontologie. Paris: Centre National de la Recherche Scientifique.
  9. ↑ Densmore, L. D.; Owen, R. D. (1989). "Molecular Systematics of the Order Crocodilia". American Zoologist . 29 (3): 831–841. doi: 10.1093/icb/29.3.831 .
  10. ↑ Norell, M. A. (1989). "The higher level relationships of the extant Crocodylia". Journal of Herpetology. 23 (4): 325–335. doi:10.2307/1564042. JSTOR   1564042.
  11. 1 2 Brochu, C. (1997). "Morphology, fossils, divergence timing, and the phylogenetic relationships of Gavialis". Systematic Biology. 46 (3): 479–522. doi:10.1093/sysbio/46.3.479. PMID   11975331.
  12. ↑ Iordansky, N. N. (1973). The skull of the Crocodilia. In: C. Gans and T. S. Parsons, eds., The Biology of the Reptilia4:201-262. London: Academic Press.
  13. ↑ Michael S. Y. Lee; Adam M. Yates (2018). "Tip-dating and homoplasy: reconciling the shallow molecular divergences of modern gharials with their long fossil record". Proceedings of the Royal Society B: Biological Sciences. 285 (1881): 20181071. doi:10.1098/rspb.2018.1071. PMC   6030529 . PMID   30051855.
  14. ↑ Gingerich, PD (1993). "Oligocene age of the Gebel Qatrani Formation, Fayum, Egypt" (PDF). Journal of Human Evolution . 24 (3): 207–218. doi:10.1006/jhev.1993.1015. hdl: 2027.42/30939 .
  15. ↑ Bown, T. M.; Kraus, M. J. (1988). "Geology and paleoenvironment of the Oligocene Jebel Qatrani Formation and adjacent rocks, Fayum Depression, Egypt". U.S. Geological Survey Professional Paper. 1452: 1–60.
  16. ↑ Gingerich, P. D. (1992). "Marine mammals (Cetacea and Sirenia) from the Eocene of Gebel Mokattam and Fayum, Egypt: stratigraphy, age, and paleoenvironments". University of Michigan Papers in Paleontology. 30: 1–84.
  17. ↑ Gagnon, M. (1997). "Ecological diversity and community ecology in the Fayum sequence (Egypt)". Journal of Human Evolution . 32 (2–3): 133–160. doi:10.1006/jhev.1996.0107. PMID   9061555.
  18. ↑ Andrews C.W. (1906). A descriptive catalogue of the tertiary vertebrata of the Fayûm, Egypt. In: British Museum (Natural History); London, UK.
  19. ↑ Vélez-Juarbe, J; Brochu, C. A.; Santos, H. (2007). "A gharial from the Oligocene of Puerto Rico: transoceanic dispersal in the history of a non-marine reptile". Proceedings of the Royal Society B: Biological Sciences. 274 (1615): 1245–1254. doi:10.1098/rspb.2006.0455. PMC   2176176 . PMID   17341454.
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