List of semiaquatic tetrapods


This is a list of tetrapods that are semiaquatic; that is, while being at least partly, they spend part of their life cycle or a significant fraction of their time in water as part of their normal behavior, and/or obtain a significant fraction of their food from an aquatic habitat. The very earliest tetrapods, such as Ichthyostega, were semiaquatic, having evolved from amphibious lobe-finned fish.
Some marine mammals, such as the marine otter, the polar bear and pinnipeds, are semiaquatic, while others, such as the sea otter, cetaceans and sirenians, are fully aquatic. The only fully aquatic nonmarine mammals are several manatees and certain small cetaceans. No bird species is fully aquatic, as all must lay and incubate their amniotic eggs, as well as begin raising their young, on land or ice. Similarly among marine reptiles, sea turtles are almost fully aquatic, but must come ashore to lay eggs. Marine iguanas and partly marine crocodiles are all semiaquatic. Most sea snakes are ovoviviparous and fully aquatic. A few freshwater snakes are also ovoviviparous and fully aquatic, but the majority are semiaquatic. Most amphibians have an aquatic larval stage and are at least semiaquatic for that reason, but there are many exceptions to this generalization.
The aquatic component of a semiaquatic species' lifestyle may be either obligatory or facultative to varying degrees.
Note: dagger symbols, "†", have been used to indicate a listed taxon is extinct.

Mammals

All extant fully aquatic mammals except the sea otter are found in two clades of exclusively aquatic species, Cetacea and Sirenia; the extinct desmostylians are also thought to have been fully aquatic. In contrast, semiaquatic mammals are widely distributed throughout the class. However, extant semiaquatic swimming marine mammals are restricted to Carnivora. Semiaquatic rodents have been noted as having larger than normal brains for their size, possibly as a consequence of using their vibrissae for acoustic detection of prey.
, a semiaquatic monotreme, Tasmania
using its trunk as a snorkel, India
, Virginia
, Europe
, Ontario
, in the Pantanal
, India
, Kenya
, Wyoming
underwater
, Norway
s, Antarctica
, Florida
s, Bolivia
, Quebec

Birds

The great majority of semiaquatic birds are found within three clades whose members are mostly semiaquatic: Aequorlitornithes, Anseriformes and Gruiformes, thought to be about 64, 47 and 41 Ma old, respectively.
Only a few nonavian dinosaurs are thought to have been semiaquatic. While the Mesozoic had many types of marine reptiles, the combination of being oviparous and endothermic seems to have prevented the evolution of fully aquatic dinosaurs, as in birds.
A number of types of pterosaurs are thought to have been piscivores, and a few are suspected of being molluscivores.
Semiaquatic forms are widely distributed among extant and extinct reptiles, and extinct semiaquatic or fully aquatic marine forms were once ecologically prominent.
s differ from other semiaquatic tetrapods in that their semiaquatic lifestyle is ancestral, rather than being the result of a secondary evolutionary trend from a terrestrial state back towards an aquatic environment. Thus, they are the only tetrapods to possess gills. All extant amphibians that are semiaquatic or fully aquatic inhabit freshwater habitats, with the exception of the crab-eating frog, which also exploits brackish habitats.
Most amphibians have an aquatic larval stage and thus are at least semiaquatic by virtue of this fact. Many adult amphibians are also semiaquatic. However, some amphibians lack an aquatic larval stage. Some frogs, such as most leiopelmatids, most ranixalids, some leptodactylids, some myobatrachids, Darwin's frog and the Seychelles frog, have nonaquatic tadpoles. Some caecilians, many frogs such as saddleback toads, most sooglossids and the greenhouse frog, and most plethodontid salamanders lay eggs on land in which the larvae develop into adult form before they hatch. The alpine salamander and African live-bearing toads are ovoviviparous and give birth on land. Additionally, about 75% of caecilians are viviparous.