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Crocodylomorpha
Fossil range: Late TriassicRecent
Protosuchus BW
Protosuchus, an early crocodylomorph
Scientific classification

Class:

Reptilia

Infraclass:

Archosauromorpha

(Unranked) :

Crurotarsi

Superorder:

Crocodylomorpha Hay, 1930

Orders:

See text.

The Crocodylomorpha are an important group of archosaurs that include the crocodilians and their extinct relatives.

During Mesozoic and Early Tertiary times, the Crocodylomorpha were far more diverse than they are now. Triassic forms were small, lightly built, active terrestrial animals. These were supplanted during the Early Jurassic by various aquatic and marine forms. The Late Jurassic, Cretaceous, and Tertiary saw a wide diversity of terrestrial and semi-aquatic lineages. "Modern" crocodilians do not appear until the Late Cretaceous.

Evolutionary history Edit

Sebecus icaeorhinus

Sebecus icaeorhinus skull

When their extinct species and stem group are examined, the crocodylian lineage (clade Crurotarsi) proves to have been a very diverse and adaptive group of reptiles. Not only are they an ancient group of animals, at least as old as the dinosaurs, they also evolved into a great variety of forms. The earliest forms, the sphenosuchians, evolved during the Late Triassic, and were highly gracile terrestrial forms built like greyhounds. During the Jurassic and the Cretaceous marine forms in the family Metriorhynchidae such as Metriorhynchus evolved forelimbs that were paddle-like and had a tail similar to modern fish. Dakosaurus andiniensis, a species closely related to Metriorhynchus, had a skull that was adapted to eat large marine reptiles. Several terrestrial species during the Cretaceous evolved herbivory, such as Simosuchus clarki and Chimaerasuchus paradoxus. A number of lineages during the Tertiary and Pleistocene became wholly terrestrial predators.

Phylogenetic definition Edit

The Crocodylomorpha are defined phylogenetically by Sereno 2005 as "The most inclusive clade containing Crocodylus niloticus (Laurenti 1768) but not Poposaurus gracilis Mehl 1915, Gracilisuchus stipanicicorum Romer 1972, Prestosuchus chiniquensis Huene 1942, Aetosaurus ferratus Fraas 1877."

This a stem-based definition and therefore includes all taxa closer to extant crocodilians than to other crurotarsan clades.

Taxonomy and phylogeny Edit

Hesperosuchus BW

Hesperosuchus, an early crocodylomorph

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 groups which variously had previously been known as Crocodilia were re-named Crocodylomorpha and the slightly more restricted Crocodyliformes.[1]

The old Crocodilia was subdivided into the suborders:

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).

The following classification is from the Bristol University webpage on Crocodylomorpha. All these taxa are extinct except for the three Eusuchian families shown here. There are in addition many other, less well-known groups that are not included in this current listing.

Phylogeny Edit

Here is the consensus of Larsson & Sues (2007) and Sereno et al. (2003):


Crocodylomorpha

Sphenosuchia


Crocodyliformes

Protosuchia


Mesoeucrocodylia

Thalattosuchia


unnamed

Notosuchia


unnamed

Sebecia


Neosuchia

Atoposauridae


unnamed

Pholidosaurus




Dyrosauridae




Sarcosuchus



Terminonaris







Goniopholididae




Bernissartia



Eusuchia










The previous definitions of Crocodilia and Eusuchia do not accurately resemble the evolution of the group. The only order-level taxon that is currently considered valid is Crocodilia in the present definition. Prehistoric crocodiles are represented by many taxa, but since few major groups of the ancient forms are recognizable, a decision where to delimit new order-level clades is not yet possible. (Benson & Clark, 1988).

References Edit

  1. ^ Martin, J.E. and Benton, M.J. (2008). "Crown Clades in Vertebrate Nomenclature: Correcting the Definition of Crocodylia." Systematic Biology, 57: 1,173 — 181.
  • 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.
  • Larsson, H. C. E., and Sues, H.-D. (2007). Cranial osteology and phylogenetic relationships of Hamadasuchus rebouli (Crocodyliformes: Mesoeucrocodylia) from the Cretaceous of Morocco. Zoological Journal of the Linnean Society 149: 533-567.
  • Sereno, P. C., Sidor, C. A., Larsson, H. C. E., and Gado, B. (2003) A new notosuchian from the Early Cretaceous of Niger. Journal of Vertebrate Paleontology 23 (2): 477-482.

External links Edit


Archosauromorphs
Primitive ArchosauromorphsEuparkeriidae • Erythrosuchidae • Proterochampsidae • Proterosuchidae • Choristodera • Prolacertiformes • Rhynchosauria • Trilophosauria

Crurotarsi ArchosaursOrnithosuchidae • Aetosauria • Phytosauria • Rauisuchia • Crocodylomorpha • Crocodilia

Avemetatarsalia and Ornithodira ArchosaursScleromochlus • Pterosauria • Dinosauromorpha • Dinosauria • Ornithischia • Saurischia • Aves

Avian ArchosaursAvialae • Archaeopteryx • Confuciusornis • Ichthyornis • Enantiornithes • Hesperornithes • Neornithes • Paleognathae • Neognathae

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