Crocodylomorpha is a group of pseudosuchian

archosaur Archosauria () or archosaurs () is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only extant taxon, extant representatives. Although broadly classified as reptiles, which traditionally exclude birds, the cladistics ...

s that includes the

crocodilia Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchia ...

ns and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. Extinct crocodylomorphs were considerably more ecologically diverse than modern crocodillians. The earliest and most primitive crocodylomorphs are represented by " sphenosuchians", a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

assemblage containing small-bodied, slender 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 The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

Evolutionary history

The earliest lineages of Crocodylomorpha are placed into the paraphyletic " Sphenosuchia", which are characterized by slender bodies with elongate legs. The oldest known crocodylomorph is '' Trialestes'', known from the Late Triassic (Carnian-Norian) of Argentina, around 231–225 million years ago, the last groups of "sphenosuchians" persisted until the end of the Jurassic. 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 Notosuchia is a clade of primarily Gondwanan mesoeucrocodylian Crocodylomorpha, crocodylomorphs that lived during the Jurassic and Cretaceous. Some phylogeny, phylogenies recover Sebecosuchia as a clade within Notosuchia, others as a sister group ...

were a diverse group across the Southern Hemisphere occupying many diverse ecologies. Modern

crocodilians Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchi ...

, a subgroup of Neosuchia, emerged during the Late Cretaceous. Crocodylomorph 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

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 Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the only pseu ...

. Crocodylomorpha has been given the rank of

superorder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...

in some 20th and 21st century studies. The old Crocodilia was subdivided into the suborders: *

Eusuchia Eusuchia is a clade of neosuchian Crocodylomorpha, crocodylomorphs that first appeared in the Early Cretaceous, which includes modern Crocodilia, crocodilians. Along with Dyrosauridae and Sebecosuchia, they were the only crocodyliformes who survi ...

: 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

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). 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). Crocodylomorpha in the modern sense, as defined by

Paul Sereno Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago who has discovered several new dinosaur species on several continents, including at sites in Inner Mongolia, Argentina, Morocco and Niger. ...

in 2005, is phylogenetically defined as the most inclusive clade containing ''

Crocodylus niloticus The Nile crocodile (''Crocodylus niloticus'') is a large crocodilian native to freshwater habitats in Africa, where it is present in 26 countries. It is widely distributed in sub-Saharan Africa, occurring mostly in the eastern, southern, and ce ...

'' (the Nile crocodile), but not '' Rauisuchus tiradentes'', '' Poposaurus gracilis'', '' Gracilisuchus stipanicicorum'', '' Prestosuchus chiniquensis'', or '' Aetosaurus ferratus''.

Phylogeny

Below is a

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

of most known crocodylomorphs from Stephan F. Speikeman in 2023. The modern consensus is that "sphenosuchians" form a paraphyletic assemblage leading towards the more derived

. The basal crocodylomorph Saltoposuchidae was defined by Speikman, 2023 as the most inclusive clade containing '' Saltoposuchus connectens'', but not '' Sphenosuchus acutus'', '' Carnufex carolinensis'', and '' Trialestes romeri''. The clade Solidocrania was established by Alexander A. Ruebenstahl and colleagues in 2022 to unite crocodyliforms with their closest "sphenosuchian" relatives who both share similarly reinforced skulls. This clade was defined as the least inclusive clade including '' Junggarsuchus sloani'', '' Almadasuchus figarii'', and '' Macelognathus vagans''.

Biology

The Crocodylomorpha comprise a variety of forms, shapes, and sizes, which occupied a range of habitats. As with most

amniote Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial animal, terrestrial and semiaquatic vertebrates. Amniotes evolution, evolved from amphibious Stem tet ...

s, Crocodylomorphs were and are

oviparous Oviparous animals are animals that reproduce by depositing fertilized zygotes outside the body (i.e., by laying or spawning) in metabolically independent incubation organs known as eggs, which nurture the embryo into moving offsprings kno ...

, 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

carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they ar ...

s, but many lineages evolved to be obligate

piscivore A piscivore () is a carnivorous animal that primarily eats fish. Fish were the diet of early tetrapod evolution (via water-bound amphibians during the Devonian period); insectivory came next; then in time, the more terrestrially adapted repti ...

s, such as the extant gharials. In some forms, like ''Hesperosuchus'' and ''Terrestrisuchus'', metatarsal V still had one or two

phalanges The phalanges (: phalanx ) are digit (anatomy), digital bones in the hands and foot, feet of most vertebrates. In primates, the Thumb, thumbs and Hallux, big toes have two phalanges while the other Digit (anatomy), digits have three phalanges. ...

, but in Crocodyliformes all metatarsal V phalanges have been lost.

References

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 The University of Bristol is a public university, public research university in Bristol, England. It received its royal charter in 1909, although it can trace its roots to a Merchant Venturers' school founded in 1595 and University College, Br ...

server *
Major subgroups
classification (used here)

from

Palaeos Palaeos.com is a web site on biology, paleontology, phylogeny and geology and which covers the history of Earth. The site is well respected and has been used as a reference by professional paleontologists such as Michael J. Benton, the professor of ...

*
Technical definition
{{Taxonbar, from=Q131863 01 Chordate superorders Extant Late Triassic first appearances Norian first appearances