page_title: Crocodilia
section_title: Relationships
hierarchical_section_title: Crocodilia / Taxonomy and classification / Relationships
caption_attribution_description: English: Skeleton of Borealosuchus wilsoni in the Field Museum of Natural History.
context_page_description: Crocodilia is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period and are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria. Members of the order's total group, the clade Pseudosuchia, appeared about 250 million years ago in the Early Triassic period, and diversified during the Mesozoic era. The order Crocodilia includes the true crocodiles, the alligators and caimans, and the gharial and false gharial. Although the term 'crocodiles' is sometimes used to refer to all of these, crocodilians is a less ambiguous vernacular term for members of this group.
  Large, solidly built, lizard-like reptiles, crocodilians have long flattened snouts, laterally compressed tails, and eyes, ears, and nostrils at the top of the head. They swim well and can move on land in a "high walk" and a "low walk", while smaller species are even capable of galloping. Their skin is thick and covered in non-overlapping scales. They have conical, peg-like teeth and a powerful bite.
context_section_description: The phylogenetic relationships of crocodilians has been the subject of debate and conflicting results. Many studies and their resulting cladograms, or "family trees" of crocodilians, have found the "short-snouted" families of Crocodylidae and Alligatoridae to be close relatives, with the long-snouted Gavialidae as a divergent branch of the tree. The resulting group of short-snouted species, name Brevirostres, was supported mainly by studies which analyzed skeletal features alone.
  In 2012, Erickson et al. produced a phylogeny formed from DNA sequencing to give a maximum likelihood cladogram of the relationships among living crocodilians (excluding the yacare caiman for which no DNA evidence was available). In this, the existence of a distinct group Brevirostres was rejected, with the long-snouted gavialids more closely related to crocodiles than to alligators.
caption: Borealosuchus wilsoni
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