Globidonta

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Globidonta
Temporal range: Late Cretaceous - Present, 82–0  Ma
Brachychampsa sp. - Natural History Museum of Utah - DSC07238.JPG
Brachychampsa sp.
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Superfamily: Alligatoroidea
Clade: Globidonta
Brochu, 1999
Subclades [1]

Globidonta is a clade of alligatoroids that includes alligators, caimans, and closely related extinct forms. It is defined as a stem-based clade including Alligator mississippiensis (the American Alligator) and all forms more closely related to it than to Diplocynodon . The group's fossil range extends back into the Late Cretaceous with early alligatoroids such as Albertochampsa and Brachychampsa . [2] Extinct globidontans were particularly common in North America and Eurasia, and their modern range also includes South America.

Basal globidontans are characterized by their blunt snouts and bulbous teeth. Modern globidontans have flattened snouts and more conical teeth, and are seen as more generalized than earlier globidontans. Generalized forms are usually expected to be ancestral to more specialized forms rather than descendants of them, so it is unusual for basal members of the group to appear specialized. This seems to conflict with the "Law of the Unspecialized" first proposed by Edward Drinker Cope in 1894. Under the Law of the Unspecialized, morphological change is always directed toward specialization, and specialized forms can never become "unspecialized" again. This pattern of change, while not seen in globidontans, can be observed in basal members of Alligatoroidea and Crocodyloidea. [3]

Alligator sinensis, the Chinese Alligator. Alligator sinensis.jpg
Alligator sinensis, the Chinese Alligator.

Flat-snouted globidontans occurred two times in the evolution of the clade: once in caimans and once in alligators. Alligator sinensis, the Chinese Alligator, has a snout that is somewhat blunt and could be considered specialized. However, its snout is not nearly as blunt as those of more basal globidontans such as Albertachampsa. [3]

If the last common ancestor of Diplocynodon and globidontans was more like Diplocynodon, it would have had a generalized snout shape. It is also possible that the generalized form of Diplocynodon may also have arisen from a specialized blunt-snouted ancestor. [3]



Phylogenetics

The below cladogram shows Globidonta's placement within Crocodylia, based on a 2018 tip dating study by Lee & Yates that simultaneously used morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data. [4]

Crocodylia
Alligatoroidea

Leidyosuchus

Diplocynodon

Globidonta

Stangerochampsa

Brachychampsa

Navajosuchus

Alligatoridae
Caimaninae

Caiman Caiman crocodilus llanos white background.JPG

Melanosuchus Melanosuchus niger white background.jpg

Paleosuchus Dwarf Caiman white background.jpg

Alligatorinae

Alligator Alligator white background.jpg

(crown group)
(stem-based group)
(stem-based group)

extinct basal Crocodilians (including Mekosuchinae )

Longirostres
Crocodyloidea

extinct basal crocodiles

Crocodylidae (crown group) Siamese Crocodile white background.jpg

(stem-based group)
Gavialoidea

extinct basal Gavialoids

Gavialidae

Gavialis Gavialis gangeticus (Gharial, Gavial) white background.jpg

Tomistoma Tomistoma schlegelii. white background.JPG

(crown group)
(stem-based group)
(crown group)
(crown group)

Here is a more detailed cladogram of Globidonta from a 2019 Massonne et al. study, with Leidyosuchus included as a member: [5]

Alligatoroidea

Diplocynodontinae

Globidonta

Leidyosuchus

Deinosuchus

Navajosuchus

Ceratosuchus

Stangerochampsa

Brachychampsa sealeyi

Brachychampsa montana

Eoalligator

Jiangxisuchus

Protoalligator

Orientalosuchus

Krabisuchus

Alligatoridae

Alligatorinae

Caimaninae

Some studies have alternatively found many members of Globidonta to instead be basal members of the crown group Alligatoridae, within either of the stem groups Alligatorinae or Caimaninae: specifically Navajosuchus and Ceratosuchus as basal members of Alligatorinae, and Stangerochampsa and Brachychampsa as basal members of Caimaninae. [6] [7]

Related Research Articles

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

Ceratosuchus is an extinct genus of alligatorine crocodylian from latest Paleocene rocks of Colorado's Piceance Basin and earliest Eocene rocks of Wyoming's Bighorn Basin in North America, a slice of time known as the Clarkforkian North American Land Mammal Age. Like its modern relatives, Ceratosuchus was a swamp-dwelling predator. It is named for the pair of flattened, triangular bony plates that extend from the back of its head.

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

Diplocynodon is an extinct genus of alligatoroid crocodilian that lived during the Paleocene to Middle Miocene in Europe. Some species may have reached lengths of 3 metres (9.8 ft), while others probably did not exceed 1 metre (3.3 ft). They are almost exclusively found in freshwater environments. The various species are thought to have been opportunistic aquatic predators.

Wannaganosuchus is an extinct genus of small alligatorid crocodilian. It was found in Late Paleocene-age rocks of Billings County, North Dakota, United States.

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

Procaimanoidea is an extinct genus of alligatorid from the Eocene of North America. It was named posthumously in 1946 by Charles W. Gilmore; the type species is P. utahensis, from the Uintan of Utah. It is based on USNM 15996, a nearly complete skull and partial left hind leg. A second species, P. kayi, was named in 1941 by C.C. Mook as a species of Hassiacosuchus, for remains from the Bridgerian of Wyoming. It was reassigned to Procaimanoidea in 1967 by Wassersug and Hecht.

Eoalligator is an extinct genus of alligatoroid crocodilian from Paleocene deposits in China.

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

Alligatoroidea is one of three superfamilies of crocodylians, the other two being Crocodyloidea and Gavialoidea. Alligatoroidea evolved in the Late Cretaceous period, and consists of the alligators and caimans, as well as extinct members more closely related to the alligators than the two other groups.

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

Allognathosuchus is an extinct genus of alligatorine crocodylian with a complicated taxonomic history. It was named in 1921.

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

Navajosuchus is an extinct genus of alligatorine crocodylian. Its fossils have been found in the Paleocene-age Nacimiento Formation of the San Juan Basin, New Mexico. It was named in 1942 by Charles C. Mook, and the original type species was N. novomexicanus. N. novomexicanus was based on AMNH 5186, a partial skull collected in 1913. Later research showed that Navajosuchus novomexicanus was the same as the earlier-named Allognathosuchus mooki. However, A. mooki does not belong to the genus Allognathosuchus, and so the name of the crocodilian becomes Navajosuchus mooki. Under whichever name is used, this animal would have been a generalized predator of the Nacimiento floodplains. It was the most common Nacimiento Formation crocodilian, found in both the Puercan and Torrejonian faunal assemblages.

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

Acynodon is an extinct genus of eusuchian crocodylomorph from the Late Cretaceous, with fossils found throughout Southern Europe.

Arambourgia is an extinct monotypic genus of alligatorine crocodylian from Europe. It was named in 1905 as Allognathosuchus gaudryi. It was made a separate genus Arambourgia in 1940. This was synonymized with Allognathosuchus haupti in 1990, but later reassigned as its own genus once again in 2004. Arambourgia was likely to have been part of an early dispersal event of alligatorines from North America to Europe during the Eocene epoch. Arambourgia had non-serrated teeth and a deep orienirostral snout, unlike the flatter snouts of most other alligatorids.

Bottosaurus is an extinct genus of alligatorid from the Late Cretaceous-Early Paleocene of New Jersey, Texas, and possibly North Carolina and South Carolina. Two species are currently accepted, with a third requiring re-evaluation.

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

Brachychampsa is an extinct genus of alligatoroid, possibly a basal caiman. Specimens have been reported from New Mexico, Colorado, Wyoming, Montana, North and South Dakota, New Jersey, and Saskatchewan, though only those from Montana, Utah, and New Mexico are based on material sufficient to justify the referral. One specimen has been reported from the Darbasa Formation of Kazakhstan, although the species status is indeterminate for the fossil. The genus first appeared during the late Campanian stage of the Late Cretaceous and became extinct during the late Maastrichtian stage of the Cretaceous. Brachychampsa is distinguished by an enlarged fifth maxillary tooth in the upper jaw.

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.

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

Stangerochampsa is an extinct genus of globidontan alligatoroid, possibly an alligatorine or a stem-caiman, from the Late Cretaceous of Alberta. It is based on RTMP.86.61.1, a skull, partial lower jaws, and partial postcranial skeleton discovered in the late Campanian–early Maastrichtian-age Horseshoe Canyon Formation. Stangerochampsa was described in 1996 by Wu and colleagues. The type species is S. mccabei. The generic name honors the Stanger family, the owners of the ranch where the specimen was found, and the species name honors James Ross McCabe, who discovered, collected, and prepared it. Stangerochampsa is described as "small to medium–sized"; the type skull is 20.0 centimetres (7.9 in) long from the tip of the snout to the occipital condyle, and is 13.0 centimetres (5.1 in) wide at its greatest, while the thigh bone is 14.2 centimetres (5.6 in) long. It had heterodont dentition, with large crushing teeth at the rear of the jaws.

Krabisuchus is an extinct genus of alligatoroid crocodylian that existed in what is now Thailand during the Eocene. It was first named by paleontologists Jeremy A. Martin and Komsorn Lauprasert in 2010, and the type species is K. siamogallicus. Fossils have been found from the Krabi Basin of southern Thailand and include mostly cranial and mandibular elements as well as some postcranial remains. Krabisuchus is currently the most well known primitive alligatoroid from Asia; previously, these animals were only represented in Asia by a few fragmentary remains from China. The fossil record of alligatoroids is much more extensive in Europe and North America, where most taxa have been described.

Culebrasuchus is an extinct, monotypic genus of caiman alligatorid known from the Early to Middle Miocene (Hemingfordian) of the Panama Canal Zone of Panama. It contains a single species, Culebrasuchus mesoamericanus.

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

Protoalligator is an extinct genus of alligatoroid crocodilian found in the Anhui province of China and lived during the Paleocene.

<span class="mw-page-title-main">Orientalosuchina</span> Extinct clade of crocodilians

Orientalosuchina is an extinct clade of alligatoroid crocodylians from South and East Asia that lived during the Paleocene and Eocene.

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

Orientalosuchus is an extinct genus of alligatoroid crocodilian from the Late Eocene that was found in the Na Duong Formation in Vietnam.

Jiangxisuchus is an extinct genus of crocodylian that lived during the Late Cretaceous in what is now China. It was described in 2019, and was proposed to be a basal member of Crocodyloidea. However, another concurrent 2019 study recovered Jiangxisuchus instead as a basal member of Alligatoroidea, within the newly named clade Orientalosuchina.

References

  1. Tobias Massonne; Davit Vasilyan; Márton Rabi; Madelaine Böhme (2019). "A new alligatoroid from the Eocene of Vietnam highlights an extinct Asian clade independent from extant Alligator sinensis". PeerJ. 7: e7562. doi: 10.7717/peerj.7562 . PMC   6839522 . PMID   31720094.
  2. Brochu, C.A. (2004). "Alligatorine phylogeny and the status of Allognathosuchus Mook, 1921". Journal of Vertebrate Paleontology. 24 (4): 857–873. doi:10.1671/0272-4634(2004)024[0857:APATSO]2.0.CO;2.
  3. 1 2 3 Brochu, C.A. (2001). "Crocodylian snouts in space and time: phylogenetic approaches toward adaptive radiation". American Zoologist. 41 (3): 564–585. CiteSeerX   10.1.1.554.231 . doi:10.1668/0003-1569(2001)041[0564:CSISAT]2.0.CO;2.
  4. Michael S. Y. Lee; Adam M. Yates (27 June 2018). "Tip-dating and homoplasy: reconciling the shallow molecular divergences of modern gharials with their long fossil". Proceedings of the Royal Society B . 285 (1881). doi: 10.1098/rspb.2018.1071 . PMC   6030529 . PMID   30051855.
  5. Tobias Massonne; Davit Vasilyan; Márton Rabi; Madelaine Böhme (2019). "A new alligatoroid from the Eocene of Vietnam highlights an extinct Asian clade independent from extant Alligator sinensis". PeerJ. 7: e7562. doi: 10.7717/peerj.7562 . PMC   6839522 . PMID   31720094.
  6. Paula Bona; Martín D. Ezcurra; Francisco Barrios; María V. Fernandez Blanco (2018). "A new Palaeocene crocodylian from southern Argentina sheds light on the early history of caimanines". Proceedings of the Royal Society B: Biological Sciences. 285 (1885): 20180843. doi:10.1098/rspb.2018.0843. PMC   6125902 . PMID   30135152.
  7. Adam P. Cossette; Christopher A. Brochu (2020). "A systematic review of the giant alligatoroid Deinosuchus from the Campanian of North America and its implications for the relationships at the root of Crocodylia". Journal of Vertebrate Paleontology. 40: e1767638. doi: 10.1080/02724634.2020.1767638 .