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Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates, including humans. Most gnathostomes have retained ancestral traits like true teeth , a stomach , [ 2 ] and paired appendages (pectoral and pelvic fins, arms, legs, wings, etc.). [ 3 ]
The earliest deposited generations of accessory teeth in each row are located at the tip of the whorl spiral labially of the primary teeth. Unlike the continuously shedding teeth of modern sharks, [7] the tooth whorls of Qianodus retained their teeth and grew in size throughout the life of the animal. The recorded gradual enlargement of the ...
The mouth is located just behind the head, after a rostrum, on the underside of the body. It has a pair of cuticular jaws, supplied by strong muscles, and often bearing minute teeth. A "basal plate" on the lower surface that bears a comb-like structure is also present.
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.
The oldest fossils appeared during the late Silurian, and became extinct at the end of the Devonian. Recent studies suggest that the placoderms are possibly a paraphyletic group of basal jawed fishes, and the closest relatives of all living jawed vertebrates. Some placoderms were small, flattened bottom-dwellers, such as antiarchs. However many ...
[2] 380-million-year-old fossils of three other genera, Incisoscutum, Materpiscis and Austroptyctodus, represent the oldest known examples of live birth. [ 3 ] Placoderms are thought to be paraphyletic , consisting of several distinct outgroups or sister taxa to all living jawed vertebrates , which originated among their ranks. [ 4 ]
According to these fossils, conodonts had large eyes, fins with fin rays, chevron-shaped muscles and axial line, which were interpreted as notochord or the dorsal nerve cord. [ 31 ] [ 35 ] While Clydagnathus and Panderodus had lengths only reaching 4–5 cm (1.6–2.0 in), Promissum is estimated to reach 40 cm (16 in) in length, if it had the ...
On each side of the skull, Tylosaurus had 2 premaxillary teeth, 12 to 13 maxillary teeth, 13 dentary teeth, and 10 to 11 pterygoid teeth. [6] The dentition is homodont , meaning that all teeth are nearly identical in size and shape, [ 93 ] [ 34 ] [ 3 ] with the exception of the pterygoid teeth, which are smaller and more recurved than the ...