Amphicotylus

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Amphicotylus
Temporal range: Late Jurassic, Tithonian
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Goniopholis skull.JPG
Skull (OMNH 2392) of Amphicotylus stovalli from Oklahoma
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauria
Clade: Pseudosuchia
Clade: Crocodylomorpha
Clade: Crocodyliformes
Family: Goniopholididae
Genus: Amphicotylus
Cope, 1878
Type species
Amphicotylus lucasii
Cope, 1878
Species [1]
  • A. felix(Marsh, 1877)
  • A. gilmorei? (Holland, 1905)
  • A. lucasiiCope, 1878
  • A. stovalli(Mook, 1964)
  • A. milesiYoshida et al., 2021 [2]

Amphicotylus is an extinct genus of goniopholidid mesoeucrocodylian from the Tithonian of Colorado, Wyoming, and Oklahoma. [3] [4] It was described in 1878. [5]

Contents

Discovery and species

Amphicotylus was first described by Edward Drinker Cope in 1878 based on dorsal and lumbar vertebrae, ribs and osteoderms. Based on these remains, found in the same locality as Camarasaurus supremus, Cope determined the animal to have been smaller in size than the extant American Alligator and named the species A. lucasii after Superintendent Lucas who initially made the discovery. [5] Cope also collected skull material from the same locality and level, however did not refer it to Amphicotylus. The cranial material was examined by Charles C. Mook in 1942 who referred it to the type species not only on the basis of its locality, but also its matching size, general morphological characters and the absence of any other crocodilian remains from the area. [6] Mook furthermore uses this skull to establish a provisional neotype to account for the fragmentary nature of the original material described by Cope.

Mounted skeleton of Amphicotylus milesi at the Gunma Museum of Natural History Amphicotylus milesi.jpg
Mounted skeleton of Amphicotylus milesi at the Gunma Museum of Natural History

In the 1930s the Works Progress Administration discovered further remains in Oklahoma which were initially investigated by J. W. Stovall, noting similarities to Amphicotylus gilmorei. The remains were officially described by Mook in 1964 as a species of Goniopholis , Goniopholis stovalli. In 2012 Eric Randall Allen argued that the goniopholidids found in the Morrison Formation differ significantly from their European counterparts in the anatomy of the palate, with the choanae fully splitting the palatines unlike in the taxa from the UK and mainland Europe. Consequently, Allen reasons that Goniopholis should exclusively refer to European forms while Amphicotylus should serve as a constituent for Morrison goniopholidids previously referred to Goniopholis, such as "Goniopholis" felix. Furthermore, it is noted that there are no significant differences between A. lucasii and the only known material of A. gilmorei, with the only notable morphological character being artificially created by breakage, rendering it a junior synonym of the genus' type species. [7]

Excavations in the East Camarasaurus Quarry, Wyoming, in 1993 yielded the largest and most complete goniopholidid skeleton found to date. Since 1996 the fossil has been exhibited and stored in the Gunma Museum of Natural History in Japan [8] before it was described by Yoshida et al. in 2021 as Amphicotylus milesi, in honor of Clifford Miles for his contribution to the excavation and museum curation. [2]

Description

Amphicotylus had a roughly triangular, platyrostral skull similar in shape to that of modern crocodilians. They differ from European goniopholidids in several morphological characters, most notably the anatomy of the palate. In members of Amphicotylus, the palatines are completely separated from one another by the choana while in Goniopholis the palatines make broad contact prior to the choana. This trait is shared by Eutretauranosuchus . [7] Amphicotylus milesi is the largest species with a skull length of 43 cm. [2]

Crocodilian respiratory system in Alligator sinensis Crocodilian respiration.gif
Crocodilian respiratory system in Alligator sinensis

The anatomy of the palate and hyoid in A. milesi show similar adaptations to extant crocodilians, with the anterior portion of the elongated choana possibly being covered in soft tissue similar to the state observed in embryos of American alligators. Based on the morphology of the hyoid apparatus and its muscle attachments, A. milesi would have been able to raise the ventral fold of the gullar valve, separating narial and oral passages. This adaptation for semi-aquatic life would have allowed Amphicotylus and other Neosuchians to completely cut out the oral cavity from respiration, giving it the ability to open its mouth underwater while continuing to breathe as long as the nares are above the surface. This pushes the development of a crocodilian-like respiratory system to the beginnings of Neosuchian evolution in the Jurassic period. [2]

Phylogeny

Studies have repeatedly found Amphicotylus to be nested deep within Goniopholididae, typically located just outside the clade that contains most European members of the group. [2] [3] [4] Denazinosuchus, a late Cretaceous member of Goniopholididae, was recovered as a sister taxon to Amphicotylus by Puértolas-Pascual et al. 2015, but as part of the "European clade" by Yoshida et al. 2021. Yoshida et al. also include Sunosuchus thailandicus without following the revisions by Martin et al. 2013 that found it to be a distinct genus of pholidosaurid, Chalawan thailandicus . The phylogenetic tree recovered by Yoshida et al. is depicted below.

Related Research Articles

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

Goniopholis is an extinct genus of goniopholidid crocodyliform that lived in Europe and North America during the Late Jurassic and Early Cretaceous. Like other goniopholidids, it resembled living crocodilians, and probably had a similar ecology as semi-aquatic ambush predators.

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

Shamosuchus is an extinct genus of neosuchian crocodyliform that lived during the Late Cretaceous (Campanian) period in what is now the Djadokhta Formation of Mongolia, approximately 75 million to 71 million years ago.

Orthosuchus is an extinct genus of crocodyliform that lived during the Early Jurassic, about 196 million years ago. It was first discovered in 1963 in the Red Beds Formation in the Qacha's Nek Province of Lesotho, southern Africa. The characteristics showed on its postcranial skeleton and the skull indicated that it is a crocodyliform. The finding is significant since some of the characteristics found on this specimen were believed to be absent until Jurassic.

Calsoyasuchus is a genus of crocodylomorph that lived in the Early Jurassic. Its fossilized remains were found in the Sinemurian-Pliensbachian-age Kayenta Formation on Navajo Nation land in Coconino County, Arizona, United States. Formally described as C. valliceps, it is known from a single incomplete skull which is unusually derived for such an early crocodile relative. This genus was described in 2002 by Ronald Tykoski and colleagues; the specific name means "valley head" and refers to a deep groove along the midline of the nasal bones and frontal bones. It has often been interpreted as the earliest diverging member of Goniopholididae, but other studies have recovered it in various other positions.

Rugosuchus is an extinct genus of neosuchian crocodyliform from the late Early Cretaceous of China. It is known from most of a skull, a partial postcranial skeleton, and a second partial skeleton including part of the hips. It was described by Xiao-Chun Wu and colleagues in 2001, with R. nonganensis as the type species. At the time of its description, it was the most complete crocodyliform from northeastern China, and only the second known.

<span class="mw-page-title-main">Goniopholididae</span> Extinct family of reptiles

Goniopholididae is an extinct family of moderate-sized semi-aquatic neosuchian crocodyliformes. Their bodyplan and morphology are convergent on living crocodilians. They lived across Laurasia between the Middle Jurassic and the Late Cretaceous.

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

Eutretauranosuchus is an extinct genus of goniopholidid crocodyliform. E. delfsi is the only known species within the genus.

<span class="mw-page-title-main">Neosuchia</span> Clade of reptiles

Neosuchia is a clade within Mesoeucrocodylia that includes all modern extant crocodilians and their closest fossil relatives. It is defined as the most inclusive clade containing all crocodylomorphs more closely related to Crocodylus niloticus than to Notosuchus terrestris. Members of Neosuchia generally share a crocodilian-like bodyform adapted to freshwater aquatic life, as opposed to the terrestrial habits of more basal crocodylomorph groups. The earliest neosuchian is suggested to be the Early Jurassic Calsoyasuchus, which lived during the Sinemurian and Pliensbachian stages in North America. It is often identified as a member of Goniopholididae, though this is disputed, and the taxon may lie outside Neosuchia, which places the earliest records of the group in the Middle Jurassic.

Brillanceausuchus is an extinct genus of paralligatorid crocodyliforms. Fossils have been found in Early Cretaceous–age rocks of Cameroon. The genus is notable for the position of the secondary choana within its palate. Parts of the pterygoid bones make up the rostral margin of the choana and thus separate it from the palatines, a feature also seen in the more advanced neosuchian suborder Eusuchia. This characteristic was once thought to be characteristic of Eusuchia, but its presence in Brillanceausuchus suggests that the trait is homoplasic, thus making the evolution of the position of the choana within crocodilians more complex than previously thought.

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

Isisfordia is an extinct genus of crocodyliform closely related to crocodilians that lived in Australia during the Middle Cretaceous (Albian–Cenomanian).

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

Pholidosaurus is an extinct genus of neosuchian crocodylomorph. It is the type genus of the family Pholidosauridae. Fossils have been found in northwestern Germany. The genus is known to have existed during the Berriasian-Albian stages of the Early Cretaceous. Fossil material found from the Annero and Jydegård Formations in Skåne, Sweden and on the island of Bornholm, Denmark, have been referred to as a mesoeucrocodylian, and possibly represent the genus Pholidosaurus.

Sunosuchus is an extinct genus of goniopholidid mesoeucrocodylian. Fossils are known from China, Kyrgyzstan, and Thailand and are Jurassic in age, although some may be Early Cretaceous. Four species are currently assigned to the genus: the type species S. miaoi and the species S. junggarensis, S. shartegensis, and S. shunanensis. All species are from China. Goniopholis phuwiangensis, also from Thailand, was reassigned to Sunosuchus by Andrade et al. (2011). The material from Kyrgyzstan has not been assigned to any species.

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

Arenysuchus is an extinct monospecific genus of allodaposuchid eusuchian crocodylomorph from Late Cretaceous deposits of north Spain. It is known from the holotype MPZ ELI-1, a partial skull from Elías site, and from the referred material MPZ2010/948, MPZ2010/949, MPZ2010/950 and MPZ2010/951, four teeth from Blasi 2 site. It was found by the researchers José Manuel Gasca and Ainara Badiola from the Tremp Formation, in Arén of Huesca, Spain. It was first named by Eduardo Puértolas, José I. Canudo and Penélope Cruzado-Caballero in 2011 and the type species is Arenysuchus gascabadiolorum.

"Crocodylus" megarhinus is an extinct species of crocodile from the Eocene of Egypt. A partial skull was found by British paleontologist Charles William Andrews in the Fayum Depression. Andrews named Crocodylus megarhinus in 1905 on the basis of the holotype skull. A complete skull was also uncovered from Egypt in 1907 but was not recognized as "C." megarhinus until 1927.

Anteophthalmosuchus is an extinct genus of goniopholidid mesoeucrocodylian from the Early Cretaceous of southern England, eastern Spain, and western Belgium.

Hulkepholis is an extinct genus of goniopholidid mesoeucrocodylian from the Early Cretaceous of southern England and eastern Spain. It contains two species, the type species, Hulkepholis willetti, and also H. plotos. Hulkepholis is most closely related to both species of Anteophthalmosuchus.

<i>Chalawan</i> (reptile) Extinct genus of reptiles

Chalawan is an extinct genus of pholidosaurid mesoeucrocodylian known from the Late Jurassic or Early Cretaceous Phu Kradung Formation of Nong Bua Lamphu Province, northeastern Thailand. It contains a single species, Chalawan thailandicus, with Chalawan shartegensis as a possible second species.

<span class="mw-page-title-main">Coelognathosuchia</span> Extinct clade of reptiles

Coelognathosuchia is an extinct clade of neosuchian crocodyliforms that includes all taxa more closely related to the family Pholidosauridae than to Bernissartia fagesii or Eusuchia. Martin et al. (2014) named the clade after finding goniopholidids and pholidosaurids to group together in their phylogenetic analysis of crocodyliform evolutionary relationships. In their analysis, Pholidosauridae was monophyletic and Goniopholididae was paraphyletic, being an assemblage of successively more basal taxa within Coelognathosuchia. Coelognathosuchia itself was positioned near the base of the larger clade Neosuchia as the sister group to a clade containing the Early Cretaceous neosuchian Bernissartia and Eusuchia, the group that includes all modern crocodilians and their closest extinct relatives.

Titanochampsa is a genus of large mesoeucrocodylian from the Maastrichtian Marilia Formation of Brazil. Although only known from a single skull roof, the material shows that Titanochampsa was not a member of Notosuchia, which were previously believed to have been the only crocodyliforms present in the strata of the Bauru Group. Body size estimates vary greatly and range between 2.98–5.88 m due to the incomplete nature of the holotype fossil. The overall anatomy of the skull roof, alongside its size and possible affinities with Neosuchians, may suggest that it was a semi-aquatic ambush hunter similar to modern crocodilians.

Ophiussasuchus is an extinct genus of goniopholidid neosuchian from the Upper Jurassic Lourinhã Formation of Portugal. It was a medium-sized goniopholidid, about 2.5 m to 3 m long, with a flattened skull and mesorostrine snout. Although most closely related to the Cretaceous goniopholids of Europe, such as Hulkepholis and Anteophthalmosuchus, Ophiussasuchus shares a variety of characteristics with more basal taxa from the Jurassic of Asia and North America. This could suggest that it either represents a transitional form or that this genus independently re-evolved these ancestral features. Ophiussasuchus is a monotypic genus, only including a single species: O. paimogonectes.

References

  1. Pritchard, A. C.; Turner, A. H.; Allen, E. R. & Norell, M. A. (2013). "Osteology of a North American Goniopholidid (Eutretauranosuchus delfsi) and Palate Evolution in Neosuchia". American Museum Novitates (3783): 1–56. doi:10.1206/3783.2. hdl:2246/6449. S2CID   73539708.
  2. 1 2 3 4 5 Yoshida, J.; Hori, A.; Kobayashi, Y.; Ryan, M.J.; Takakuwa, Y.; Hasegawa, Y. (8 December 2021). "A new goniopholidid from the Upper Jurassic Morrison Formation, USA: novel insight into aquatic adaptation toward modern crocodylians". The Royal Society. 8 (12). doi: 10.1098/rsos.210320 . PMC   8652276 . PMID   34909210.
  3. 1 2 Marco Brandalise de Andrade; Richard Edmonds; Michael J. Benton & Remmert Schouten (2011). "A new Berriasian species of Goniopholis (Mesoeucrocodylia, Neosuchia) from England, and a review of the genus". Zoological Journal of the Linnean Society. 163 (s1): S66–S108. doi:10.1111/j.1096-3642.2011.00709.x.
  4. 1 2 Puértolas-Pascual, E.; Canudo, J.I. & Sender, L.M. (2015). "New material from a huge specimen of Anteophthalmosuchus cf. escuchae (Goniopholididae) from the Albian of Andorra (Teruel, Spain): Phylogenetic implications". Journal of Iberian Geology. 41 (1): 41–56. doi: 10.5209/rev_JIGE.2015.v41.n1.48654 .
  5. 1 2 E. D. Cope. 1878. Descriptions of new extinct Vertebrata from the Upper Tertiary and Dakota Formations. 'Bulletin of the United States Geological and Geographical Survey of the Territories, 4(2):379-396
  6. Mook, C.C. (2 April 1942). "Skull Characters of Amphicotylus lucasii Cope". American Museum Novitates (1165).
  7. 1 2 Allen, E.R. (2012). "Analysis of North American goniopholidid crocodyliforms in a phylogenetic context". M.C. thesis, University of Iowa.
  8. "水中適応では最古...ワニ祖先の新種 福島県立博物館のグループ" [The oldest in water adaptation: A group of new species of crocodile ancestors at the fukushima prefectural museum]. 9 December 2021. Retrieved 9 December 2021.