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The fins evolved into the legs of the first tetrapod land vertebrates, amphibians. They also possess two dorsal fins with separate bases, as opposed to the single dorsal fin of ray-finned fish. The braincase of lobe-finned fish primitively has a hinge line, but this is lost in tetrapods and lungfish.
The coelacanth was long considered a "living fossil" because scientists thought it was the sole remaining member of a taxon otherwise known only from fossils, with no close relations alive, [8] and that it evolved into roughly its current form approximately 400 million years ago. [1]
A subclass of bony fish, the ray-finned fishes (Actinopterygii), have become the dominant group in the post-Paleozoic and modern world, with some 30,000 living species. Meanwhile, another subclass of bony fish, the lobe-finned fishes, became the dominant group on land. Sea levels in the Devonian were generally high.
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 study of prehistoric fish is called paleoichthyology. A few living forms, such as the coelacanth are also referred to as prehistoric fish, or even living fossils, due to their current rarity and similarity to extinct forms. Fish which have become recently extinct are not usually referred to as prehistoric fish.
A newfound fossil of a jawless fish is the oldest known vertebrate cranium preserved in 3D. The 455 million-year-old find could illuminate how vertebrate heads evolved.
Placoderms were among the first jawed fish (their jaws likely evolved from the first pair of gill arches), as well as the first vertebrates to have true teeth. They were also the first fish clade to develop pelvic fins, the second set of paired fins and the homologous precursor to hindlimbs in tetrapods.
One of the persistent questions facing paleontologists is the evolution of the tetrapod limb: specifically, how the internal bones of lobed fins evolved into the feet and toes of tetrapods. In many lobe-finned fish, including living coelacanths and the Australian lungfish , the fin skeleton is based around a straight string of midline bones ...