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A notable characteristic that make a tetrapod's skull different from a fish's are the relative frontal and rear portion lengths. The fish had a long rear portion while the front was short; the orbital vacuities were thus located towards the anterior end. In the tetrapod, the front of the skull lengthened, positioning the orbits farther back on ...
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 fossil record of early tetrapods shows evidence of distinct pelvic development occurring in osteolepiforms, further supporting osteolepiform ancestry of terrestrial tetrapods. [4] Acanthostega has a large pelvis, with the iliac region articulating with the axial skeleton and a broad ischial plate. [3]
The endoskeleton of the fish is made up of two main components: the axial skeleton consisting of the skull and vertebral column, and the appendicular skeleton supporting the fins. [7] The fins are made up of bony fin rays and, except for the caudal fin, have no direct connection with the spine.
The fin has both a robust internal skeleton, like tetrapods, surrounded by a web of simple bony fin rays (lepidotrichia), like fish. [1] The lepidotrichia are thickest and most extensive on the front edge and upper side of the fin, leaving more room for muscle and skin on the underside of the fin. [ 2 ]
Ichthyostega (from Greek: ἰχθῦς ikhthûs, 'fish' and Greek: στέγη stégē, 'roof') is an extinct genus of limbed tetrapodomorphs from the Late Devonian of what is now Greenland. It was among the earliest four-limbed vertebrates ever in the fossil record and was one of the first with weight-bearing adaptations for terrestrial locomotion.
Osteichthyes (/ ˌ ɒ s t iː ˈ ɪ k θ iː z / ost-ee-IK-theez; from Ancient Greek ὀστέον (ostéon) ' bone ' and ἰχθύς (ikhthús) ' fish '), [2] also known as osteichthyans or commonly referred to as the bony fish, is a diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue.
Marine tetrapods are tetrapods that returned from land back to the sea again. The first returns to the ocean may have occurred as early as the Carboniferous Period [ 20 ] whereas other returns occurred as recently as the Cenozoic , as in cetaceans, pinnipeds , [ 21 ] and several modern amphibians .