Biology:Globidonta

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Short description: Clade of reptiles

Globidonta
Temporal range: Late Cretaceous - Present, 82–0 Ma
Brachychampsa sp. - Natural History Museum of Utah - DSC07238.JPG
Brachychampsa sp.
Scientific classification e
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauromorpha
Clade: Archosauriformes
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.

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]

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. 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:APATSO2.0.CO;2]. 
  3. 3.0 3.1 3.2 Brochu, C.A. (2001). "Crocodylian snouts in space and time: phylogenetic approaches toward adaptive radiation". American Zoologist 41 (3): 564–585. doi:10.1668/0003-1569(2001)041[0564:CSISAT2.0.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. 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. 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. 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. 


Wikidata ☰ Q5571040 entry