Search results
Results from the WOW.Com Content Network
The tetrapods, including all large- and medium-sized land animals, have been among the best understood animals since earliest times. By Aristotle 's time, the basic division between mammals, birds and egg-laying tetrapods (the " herptiles ") was well known, and the inclusion of the legless snakes into this group was likewise recognized. [ 28 ]
The distinction between quadrupeds and tetrapods is important in evolutionary biology, particularly in the context of tetrapods whose limbs have adapted to other roles (e.g., hands in the case of humans, wings in the case of birds and bats, and fins in the case of whales). All of these animals are tetrapods, but not all are quadrupeds.
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. [1] Tetrapods (under the apomorphy-based definition used on this page) are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals.
Tetrapods (animals with four limbs) 395 Amniota: Amniotes (fully terrestrial tetrapods whose eggs are "equipped with an amnion") 340 Synapsida: Proto-Mammals 308 Therapsid: Limbs beneath the body and other mammalian traits 280 Class: Mammalia: Mammals: 220 Subclass: Theria: Mammals that give birth to live young (i.e. non-egg-laying) 160 ...
Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial and semiaquatic vertebrates. Amniotes evolved from amphibious stem tetrapod ancestors during the Carboniferous period.
Tiktaalik, a lobe-finned fish with some anatomical features similar to early tetrapods. It has been suggested to be a transitional species between fish and tetrapods. [81] 365 Ma Acanthostega is one of the earliest vertebrates capable of walking. [82] 363 Ma By the start of the Carboniferous Period, the Earth begins to resemble its present state.
Several groups of tetrapods, such as the reptillian snakes and mammalian cetaceans, have lost some or all of their limbs, and many tetrapods have returned to partially aquatic or (in the case of cetaceans and sirenians) fully aquatic lives. The tetrapods evolved from the lobe-finned fishes about 395 million years ago in the Devonian. [23]
Another example of this is with humans and chimps. Humans contain numerous ERVs that comprise a considerable percentage of the genome. Sources vary, but 1% [36] to 8% [37] has been proposed. Humans and chimps share seven different occurrences of virogenes, while all primates share similar retroviruses congruent with phylogeny. [38] [39]