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Whales have two flippers on the front, and a tail fin. These flippers contain four digits. Although whales do not possess fully developed hind limbs, some, such as the sperm whale and bowhead whale, possess discrete rudimentary appendages, which may contain feet and digits.
Only one species of primate, the Calabar angwantibo, is known to have a functioning nictitating membrane. [ 44 ] The orbitalis muscle is a vestigial or rudimentary nonstriated muscle (smooth muscle) of the eye that crosses from the infraorbital groove and sphenomaxillary fissure and is intimately united with the periosteum of the orbit.
This made it possible for whales to move around with the vertical tail hitting the water. The front legs transformed into flippers, costing them their mobility on land. [82] One of the oldest members of ancient cetaceans (Archaeoceti) is Pakicetus from the Middle Eocene of Pakistan. This is an animal the size of a wolf, whose skeleton is known ...
Baleen whales have two flippers on the front, near the head. Like all mammals, baleen whales breathe air and must surface periodically to do so. Their nostrils, or blowholes, are situated at the top of the cranium. Baleen whales have two blowholes, as opposed to toothed whales which have one.
The holotype of R. kasrani, GSP-UM 3012 found in 1992, was described by Gingerich et al. 1994: a cranium with two dentaries, most of the vertebral column as far as the anterior tail (C2–C7; T1–13; L1–6, S1–4, Ca1–4), most ribs, parts of the sternum, both hip bones, and a left femur.
[3] [4] Parts recovered include the jaw, front and hind legs, bits of spine, and tail. Olivier Lambert, a scientist at the Royal Belgian Institute of Natural Sciences and lead author of the study, noted that Peregocetus "fills in a crucial [knowledge] gap" about the evolution of whales and their spread.
It’s a creature of the deep so rare that there’s never been a recorded live sighting, and since the 1800s only six samples have ever been documented.
Unlike all later cetaceans, it had four fully functional long legs. Pakicetus had a long snout; a typical complement of teeth that included incisors, canines, premolars, and molars; a distinct and flexible neck; and a very long and robust tail. As in most land mammals, the nose was at the tip of the snout.