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The term ichthyopsida means fish-face or fish-like as opposed to the Sauropsida or lizard-face animals (reptiles and birds) and the mammals. [6] The group representing an evolutionary grade rather than a clade , the term anamniote is now used as an informal way of denoting the physical property of the group, rather than as a systematic unit.
While the early amniotes resembled their amphibian ancestors in many respects, a key difference was the lack of an otic notch at the back margin of the skull roof. In their ancestors, this notch held a spiracle , an unnecessary structure in an animal without an aquatic larval stage. [ 25 ]
Some amphibians such as newts and salamanders, and some frogs such as fire-bellied toads and wood frogs. Some reptiles such as crocodilians, turtles, water snakes and marine iguanas. Waterbirds, especially penguins, waterfowls, storks and shorebirds. Some rodents such as beavers, muskrats and capybaras.
Instead, they consistute an evolutionary grade (a paraphyletic group), ancestral to living tetrapods such as lissamphibians (modern amphibians) and amniotes (reptiles, mammals, and kin). "Labyrinthodont"-grade vertebrates evolved from lobe-finned fishes in the Devonian , though a formal boundary between fish and amphibian is difficult to define ...
Primates have a longer juvenile period between weaning and sexual maturity than other mammals of similar size. [57] Some primates such as galagos and New World monkeys use tree-holes for nesting, and park juveniles in leafy patches while foraging. Other primates follow a strategy of "riding", i.e. carrying individuals on the body while feeding.
The largest living amphibian is the 1.8 m (5 ft 11 in) Chinese giant salamander (Andrias davidianus) [41] but this is a great deal smaller than the largest amphibian that ever existed—the extinct 9 m (30 ft) Prionosuchus, a crocodile-like temnospondyl dating to 270 million years ago from the middle Permian of Brazil. [42]
Synapsida [a] is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant reptiles and birds).
The evolutionary split between placentals and marsupials occurred 125-160 million years ago, in the Middle Jurassic-Early Cretaceous period. Presently, close to 70% of the 334 extant marsupial species are concentrated on the Australian continent, including mainland Australia, Tasmania, New Guinea, and nearby islands.