Crocodilians appeared 83.5 million years ago beside bird kin
Crocodylia is the order of semiaquatic predatory reptiles we call crocodilians. Fossils place them from about 83.5 million years ago in the Late Cretaceous Campanian, and living members are birds’ closest reptile relatives among surviving lineages. Every species, from dwarf caiman to Nile crocodile, shares essentially one body plan.
Crocodylia is defined as the last common ancestor of the gharial, the American alligator and the Cuban crocodile together with all its descendants. The spellings Crocodilia and Crocodylia have been swapped freely for decades: Karl Patterson Schmidt revived Richard Owen's older Crocodilia, while Heinz Wermuth preferred Crocodylia after the type genus Crocodylus. Wermuth's form seems to draw on Greek words for pebble and worm.
Crocodilians and birds both belong to Archosauria, reptiles marked by extra skull openings in front of the eye and in the lower jaw. The crocodile line, Crocodylomorpha, arose in the Late Triassic from small, slender, long-legged 'sphenosuchians' that chased fast prey. In the Jurassic, crocodylomorphs spread into niches left by extinct groups, becoming insectivores, fish specialists and ocean dwellers far more varied than today's species.
The three main branches of the crown group had split by the Late Cretaceous, with Portugalosuchus and Zholsuchus as disputed early members. DNA sequencing has discarded the older grouping Brevirostres by showing that gharials sit closer to crocodiles than to alligators, and that pairing is now called Longirostres. A 2021 mitochondrial analysis even drew on genetic material from the recently extinct Voay robustus.
Despite varied snouts and teeth, every species is built on a stout barrel of a body with a flattened head, lengthy snout, stubby neck and a tail squeezed flat from side to side, with eyes, ears and nostrils on top of the head. Alligators and caimans usually show only upper teeth when the U-shaped jaw closes, whereas the narrower V-shaped jaws of crocodiles leave both rows visible. Sizes run from dwarf caimans of 1 to 1.5 metres to Nile and saltwater crocodiles of 6 metres, and the Miocene caiman Purussaurus may have topped 10 metres. Hunting, poaching and habitat loss are the chief threats, though farming has sharply cut illegal trade in wild skins.
Source: Crocodylia
