Ideally, the flipper is first moved obliquely to the front and downwards and then, after a slight retraction and rotation, crosses this path from below to be pulled to the front and upwards. Its size, long neck, and four whale-like flippers make it unmistakable for any other creature. Plesiosaur, any of a group of long-necked marine reptiles found as fossils from the Late Triassic Period into the Late Cretaceous Period (215 million to 80 million years ago). [137] Frequent explanations for the sightings include waves, floating inanimate objects, tricks of the light, swimming known animals and practical jokes. Quagga, Anu ■ Later, a more advanced pistosaurian group split off: the Plesiosauria. This analysis focused on basal plesiosaurs and therefore only one derived pliosaurid and one cryptoclidian were included, while elasmosaurids were not included at all. The Plesiosauroidea, such as Cryptoclididae, Elasmosauridae, and Plesiosauridae had long necks and may have been bottom-feeders, in shallow waters. In 2012, a mandible of Pliosaurus was described with a jaw joint clearly afflicted by arthritis, a typical sign of senescence. The vertebrae show no such damage: they were probably protected by a superior blood supply, made possible by the arteries entering the bone through the two foramina subcentralia, large openings in their undersides. Hawkins entertained a very idiosyncratic view of the animals,[15] seeing them as monstrous creations of the devil, during a pre-Adamitic phase of history. Digestion of shellfish was aided by gastroliths. The nostrils of Plesiosaurus were positioned closer to its eyes than the tip of its snout. [66][67][68] A 2020 study claims that the caudal fin was horizontal in configuration.[69]. The size of the stones has been seen as an indication that they were not swallowed by accident but deliberately, the animal perhaps covering large distances in search of a suitable rock type. However, some at least were bottom-feeders, consuming various prey. Such a clade is called a "stem clade". According to one hypothesis, during its passage through the nasal ducts, the water would have been 'smelled' by olfactory epithelia. Frey & Riess would have been mistaken in their assertion that the shoulder and pelvic plates had no muscles attached to their upper sides. Head of medium size, neck fairly thick and strong, up to 30 vertebrae. Often, the lacrimal bones were also lacking.[47]. [70] The bony fish (Osteichthyes), which further diversified during the Jurassic, were likely prey as well. Plesiosaurus; Cryptoclidids: longer necks, with more than 30 vertebrae. Plesiosaurs gave birth to just one individual, allowing us to make inferences on the degree of maternal care. ), Ancient Marine Reptiles, Academic Press, San Diego. Williston, S. W. 1903. Size and Weight: About 25 feet long and 1-2 tons Diet: Plankton and krill Distinguishing Characteristics: Long neck; numerous, needle-shaped teeth Aristonectes' fine, numerous, needle-shaped teeth are a dead giveaway that this plesiosaur subsisted on plankton and krill (small crustaceans) rather than larger fare. She found it on the 'Jurassic Coast' of Dorset, England in the winter of 1820/21. [44] The Pistosauria became warm-blooded and viviparous, giving birth to live young. In December 2017, a large skeleton of a plesiosaur was found in the continent of Antarctica, the oldest creature on the continent, and the first of its species in Antarctica. Their relative brain size seems to be typical for reptiles. Rayner and R.J. Wootton (eds.