Crocodylomorpha

Crocodylomorphs Temporal range: Late Triassic–Present,
Skeleton of Terrestrisuchus, an early saltoposuchid crocodylomorph
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauria
Clade:	Pseudosuchia
Clade:	Paracrocodylomorpha
Clade:	Loricata
Clade:	Crocodylomorpha Hay, 1930
Subgroups
†Artzosuchus? †Carnufex †Dianchungosaurus †Dibothrosuchus †Dromicosuchus †Hesperosuchus †Kayentasuchus †Parrishia? †Pseudhesperosuchus †Redondavenator †Sphenosuchus †Syntomiprosopus? †Trialestes Saltoposuchidae Crush, 1984 †Litargosuchus †Saltoposuchus †Terrestrisuchus Solidocrania Ruebenstahl et al., 2022 †Junggarsuchus †Phyllodontosuchus? †Hallopodidae †Thalattosuchia Crocodyliformes

Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction.

During Mesozoic and early Cenozoic times, crocodylomorphs were far more diverse than at Present. Triassic forms were small, lightly built, active terrestrial animals. The earliest and most primitive crocodylomorphs are represented by "sphenosuchians", a paraphyletic assemblage containing small-bodied forms with elongated limbs that walked upright, which represents the ancestral morphology of Crocodylomorpha. These forms persisted until the end of the Jurassic. During the Jurassic, crocodylomorphs morphologically diversified into numerous niches, with the subgroups Neosuchia (which includes modern crocodilians) and the extinct Thalattosuchia adapting to aquatic life, while some terrestrial groups adopted herbivorous and omnivorous lifestyles. Terrestrial crocodylomorphs would continue to co-exist alongside aquatic forms until becoming extinct during the Miocene.

Evolutionary history

Life restoration of Hesperosuchus

The earliest lineages of Crocodylomorpha are placed into the paraphyletic "Sphenosuchia", which are charactersed by slender bodies with elongate legs. The oldest known crocodylmorph is Trialestes, known from the Late Triassic (Carnian-Norian) of Argentina, around 231–225 million years ago. During the Jurassic, crocodylomorphs diversified, including the emergence of herbivorous and omnivorous forms, as well as the aquatically adapted Neosuchia and Thalattosuchia, with Thalattosuchia and several groups of neosuchians becoming adapted to a marine lifestyle over the Jurassic and Cretaceous During the Cretaceous, the Notosuchia were a diverse group across the Southern Hemisphere occupying many diverse ecologies. Modern crocodilians, a subgroup of Neosuchia, emerged during the Late Cretaceous. Crocodylmorph diversity was severely reduced by the end-Cretaceous extinction event. The last group of terrestrially adapted crocodylomorphs was the Sebecidae, a group of large predatory notosuchians which persisted in South America until the middle Miocene around 12 million years ago.

Taxonomy and phylogeny

Historically, all known living and extinct crocodiles were indiscriminately lumped into the order Crocodilia. However, beginning in the late 1980s, many scientists began restricting the order Crocodilia to the living species and close extinct relatives such as Mekosuchus. The various other groups that had previously been known as Crocodilia were moved to Crocodylomorpha and the slightly more restrictive Crocodyliformes. Crocodylomorpha has been given the rank of superorder in some 20th and 21st century studies.

The old Crocodilia was subdivided into the suborders:

• Eusuchia: true crocodiles (which includes crown-group Crocodylia)
• Mesosuchia: 'middle' crocodiles
• Thalattosuchia: sea crocodiles
• Protosuchia: first crocodiles
• Sphenosuchia: wedge crocodiles
• Sebecosuchia: Sebecus crocodiles

Mesosuchia is a paraphyletic group as it does not include eusuchians (which nest within Mesosuchia). Mesoeucrocodylia was the name given to the clade that contains mesosuchians and eusuchians (Whetstone and Whybrow, 1983).

Phylogeny

Below is a cladogram modified from Nesbitt (2011) and Bronzati (2012).

Crocodylomorpha	CM 73372 Hesperosuchus Dromicosuchus Sphenosuchus Dibothrosuchus Terrestrisuchus Litargosuchus Kayentasuchus  Crocodyliformes  Protosuchia  Metasuchia  Notosuchia Neosuchia

The previous definitions of Crocodilia and Eusuchia did not accurately convey evolutionary relationships within the group. The only order-level taxon that is currently considered valid is Crocodilia in its present definition. Prehistoric crocodiles are represented by many taxa, but since few major groups of the ancient forms are distinguishable, a conclusion on how to define new order-level clades is not yet possible. (Benson & Clark, 1988).

Biology

The Crocodylomorpha comprise a variety of forms, shapes, and sizes, which occupied a range of habitats. As with most amniotes, Crocodylomorphs were and are oviparous, laying eggs in a nest or mound, known from strata as old as the Late Jurassic. Adult size varies widely, from about 55 cm long in Knoetschkesuchus to much larger dimensions, as in Sarcosuchus. Most crocodylomorphs were carnivores, but many lineages evolved to be obligate piscivores, such as the extant gharials.

Sources

• Benton, M. J. (2004), Vertebrate Palaeontology, 3rd ed. Blackwell Science Ltd
• Hay, O. P. 1930 (1929–1930). Second Bibliography and Catalogue of the Fossil Vertebrata of North America. Carnegie Institution Publications, Washington, 1, 990 pp.

External links

• Crocodylomorpha - webpages by Ross Elgin on the University of Bristol server
  • Major subgroups classification (used here)
• Crocodylomorpha from Palaeos
  • Technical definition