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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.
The world's smallest known vertebrate, Paedophryne amauensis, sitting on a U.S. dime.The dime is 17.9 mm in diameter, for scale. The word amphibian is derived from the Ancient Greek term ἀμφίβιος (amphíbios), which means 'both kinds of life', ἀμφί meaning 'of both kinds' and βίος meaning 'life'.
The unique embryonic features of amniotes may reflect specializations for eggs to survive drier environments; or the increase in size and yolk content of eggs may have permitted, and coevolved with, direct development of the embryo to a large size.
However, many such endemic species are related to species found on other nearby islands or continents; the relationship of the animals found on the Galápagos Islands to those found in South America is a well-known example. [140] All of these facts, the types of plants and animals found on oceanic islands, the large number of endemic species ...
The common descent of organisms was first deduced from four simple facts about organisms: First, they have geographic distributions that cannot be explained by local adaptation. Second, the diversity of life is not a set of unique organisms, but organisms that share morphological similarities.
X-ray showing the skeleton of Typhlonectes (Typhlonectidae). Caecilians' anatomy is highly adapted for a burrowing lifestyle. In a couple of species belonging to the primitive genus Ichthyophis vestigial traces of limbs have been found, and in Typhlonectes compressicauda the presence of limb buds has been observed during embryonic development, remnants in an otherwise completely limbless body. [7]
Trunk, a single woody stem came about in unrelated plants: paleozoic tree forms of club mosses, horsetails, and seed plants. The marine animals sea lily crinoid, looks like a terrestrial palm tree. [228] Palm trees form are in unrelated plants: cycads (from the Jurassic period) and older tree ferns. [229]
The temnospondyl Eryops had sturdy limbs to support its body on land Red-eyed tree frog (Agalychnis callidryas) with limbs and feet specialised for climbing Japanese giant salamander (Andrias japonicus), a primitive salamander The bright colours of the common reed frog (Hyperolius viridiflavus) are typical of a toxic species Wallace's flying frog (Rhacophorus nigropalmatus) can parachute to ...