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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 .
[8] [27] Coelacanths are large, plump, lobe-finned fish that can grow to more than 2 m (6.6 ft) and weigh around 90 kg (200 lb). [28] They are estimated to live up to 100 years, based on analysis of annual growth marks on scales, and reach maturity around the age of 55; [ 29 ] the oldest known specimen was 84 years old at the time of its ...
Brachydegma is an extinct genus of prehistoric freshwater ray-finned fish that lived during the Leonardian age (Cisuralian/lower Permian) in what is now Texas, United States.It is known from two fossils, which were recovered from the Clear Fork Formation.
Xenacanthida (or Xenacanthiformes) is an order or superorder of extinct shark-like chondrichthyans (cartilaginous fish) known from the Carboniferous to Triassic. They were native to freshwater, marginal marine and shallow marine habitats. [1] Some xenacanths may have grown to lengths of 5 m (16 ft). [2]
The individual teeth are widely separated from each other in the tooth whorls. [16] The teeth themselves are of the cladodont variety; the bases of the teeth are broadest on the lingual side, and each support a single large cusp and two pairs of smaller accessory cusps for a total of five cusps. [16]
Acanthodii or acanthodians is an extinct class of gnathostomes (jawed fishes).They are currently considered to represent a paraphyletic grade of various fish lineages basal to extant Chondrichthyes, which includes living sharks, rays, and chimaeras.
Helicoprion is a genus of extinct shark-like [1] eugeneodont fish. Almost all fossil specimens are of spirally arranged clusters of the individuals' teeth, called "tooth whorls", which in life were embedded in the lower jaw. As with most extinct cartilaginous fish, the skeleton is mostly unknown.
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.