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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 ]
A mastodon (mastós 'breast' + odoús 'tooth') is a member of the genus Mammut (German for 'mammoth'), which was endemic to North America and lived from the late Miocene to the early Holocene.
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.
Regions of a Chondrichthyes brain colored and labeled on dissected skate. The rostral end of the skate is to the right. In chondrichthyans, the nervous system is composed of a small brain, 8–10 pairs of cranial nerves, and a spinal cord with spinal nerves. [11] They have several sensory organs which provide information to be processed.
The echidna's brain is half neocortex, [17] compared to 80% of a human brain. [18] [19] Contrary to previous research, the echidna does enter REM sleep, but only in a comfortable temperature around 25 °C (77 °F). At lower or higher temperatures of 15 °C (59 °F) and 28 °C (82 °F), REM sleep is suppressed. [20]
First and foremost was the fact that the British scientific establishment had been fooled by the hoax of the Piltdown Man, which had a large brain and ape-like teeth. [15] Expecting human ancestors to have evolved a large brain very early, they found that the Taung Child's small brain and human-like teeth made it an unlikely ancestor to modern ...
A study of the arthrodire Compagopiscis published in 2012 concluded that placoderms (at least this particular genus) likely possessed true teeth contrary to some early studies. The teeth had well defined pulp cavities and were made of both bone and dentine. However, the tooth and jaw development were not as closely integrated as in modern ...
Conodont elements consist of mineralised teeth-like structures of varying morphology and complexity. The evolution of mineralized tissues has been puzzling for more than a century. It has been hypothesized that the first mechanism of chordate tissue mineralization began either in the oral skeleton of conodonts or the dermal skeleton of early ...