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Several groups of tetrapods have undergone secondary aquatic adaptation, an evolutionary transition from being purely terrestrial to living at least part of the time in water. These animals are called "secondarily aquatic" because although their ancestors lived on land for hundreds of millions of years, they all originally descended from ...
The specific aquatic ancestors of the tetrapods and the process by which they colonized Earth's land after emerging from water remains unclear. The transition from a body plan for gill -based aquatic respiration and tail -propelled aquatic locomotion to one that enables the animal to survive out of water and move around on land is one of the ...
Acanthostega is a partially aquatic tetrapod with developed limbs that shares features common with the earlier tetrapods, Panderichthys and Eusthenopteron. [3] Like Panderichthys , the humerus of Acanthostega is flattened dorso-ventrally, the intermedium terminates level with the radius, and the endoskeleton can be divided into stylopodium ...
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.
Polydactyly in early tetrapod aquatic animals, such as in Acanthostega gunnari (Jarvik 1952), one of an increasing number of genera of stem-tetrapods known from the Upper Devonian, which are providing insights into the appearance of tetrapods and the origin of limbs with digits. It also occurs secondarily in some later tetrapods, such as ...
The aquatic ancestors of tetrapods did not have a sacrum, so it was speculated to have evolved for locomotive function exclusive to terrestrial environments. However, the Acanthostega species is one of the earliest lineages to have a sacrum, even though it is a fully aquatic species. Once species moved onto land, the trait was adapted for ...
Suborder Charadrii (plover-like waders). Family Charadriidae (plovers and lapwings); Family Haematopodidae (oystercatchers); Family Ibidorhynchidae (ibisbill); Family Recurvirostridae (avocets and stilts)
Dvinosaurus is thought to have been a gill-breathing, fully-aquatic tetrapod, characterized by a large, triangular head, short limbs, and a long powerful tail. [3] A typical individual could grow to be approximately 40 in (100 cm) in length. [3] Within this genus, the number of documented species has varied over the years since its discovery.