Crocodilia is an order of mostly large, predatory, semiaquatic reptiles known as crocodilians. They first appeared 94 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.
Crocodilia
Restoration of early crocodylomorph Protosuchus
Skeletal mount of the giant crocodylian Deinosuchus from the Late Cretaceous of North America
Mounted skeleton and taxidermy of Nile crocodile
In biology, being semiaquatic refers to various macroorganisms that live regularly in both aquatic and terrestrial environments. When referring to animals, the term describes those that actively spend part of their daily time in water, or land animals that have spent at least one life stages in aquatic environments. When referring to plants, the term describes land plants whose roots have adapted well to tolerate regular, prolonged submersion in water, as well as emergent and (occasionally) floating-leaved aquatic plants that are only partially immersed in water.
The common frog, one of the most ubiquitous semiaquatic amphibians in Europe
Atlantic mudskippers, amphibious fish of mangrove swamps and tidal flats
Pachygrapsus marmoratus, a semiterrestrial crab
Hunting stance of Dolomedes minor, a semiaquatic spider