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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 ]
In a letter dating to 1713, Edward Hyde, 3rd Earl of Clarendon (known also as Lord Cornbury) from New York reported to the Royal Society learned society of Great Britain that in 1705, a large-sized tooth was found near the side of the Hudson River by a Dutch country-fellow and was sold to New York General Assembly member Van Bruggen for a gill ...
The evolution of the mammalian middle ear appears to have occurred in two steps. A partial middle ear formed by the departure of postdentary bones from the dentary, and happened independently in the ancestors of monotremes and therians. The second step was the transition to a definite mammalian middle ear, and evolved independently at least ...
This arch divides into a maxillary process and a mandibular process, giving rise to structures including the bones of the lower two-thirds of the face and the jaw. The maxillary process becomes the maxilla (or upper jaw, although there are large differences among animals [11]), and palate while the mandibular process becomes the mandible or lower jaw.
The three forms of teeth, i.e., coniform cones, ramiform bars, and pectiniform platforms, probably performed different functions. For many years, conodonts were known only from enigmatic tooth-like microfossils (200 micrometers to 5 millimeters in length [ 17 ] ), which occur commonly, but not always, in isolation and were not associated with ...
The mastoid antrum (tympanic antrum, antrum mastoideum, Valsalva's antrum) is an air space in the petrous portion of the temporal bone, communicating posteriorly with the mastoid cells and anteriorly with the epitympanic recess of the middle ear via the aditus to mastoid antrum (entrance to the mastoid antrum). These air spaces function as ...
The nasal opening, which eventually becomes the blowhole in modern cetaceans, was located near the tip of the snout. The position of the nasal opening had remained unchanged since pakicetids. [ 18 ] One of the notable features in remingtonocetids is that the semicircular canals , which are important for balancing in land mammals, had decreased ...
Brontotheriidae is a family of extinct mammals belonging to the order Perissodactyla, the order that includes horses, rhinoceroses, and tapirs.Superficially, they looked rather like rhinos with some developing bony nose horns, and were some of the earliest mammals to have evolved large body sizes of several tonnes.