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The Plesiosauria[ a ][ 4 ] or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared in the latest Triassic Period, possibly in the Rhaetian stage, about 203 million years ago. [ 5 ] They became especially common during the Jurassic Period, thriving until their ...
Plesiosaurus is the archetypical genus of Plesiosauria and the first to be described, hence lending its name to the order. Conybeare and De la Beche coined the name for scattered finds from the Bristol region, Dorset, and Lyme Regis in 1821. [6] The type species of Plesiosaurus, P. dolichodeirus, was named and described by Conybeare in 1824 on ...
Pliosaurus brachyspondylus was first described and named by Owen in 1839, as a species of Plesiosaurus. The specific name is derived from βραχυς, brachus, meaning "short" and σπόνδυλος, spondylos, meaning "vertebra" in Ancient Greek. [ 22 ] It was named on the basis of a series of unassociated cervical vertebrae as the holotype.
Elasmosaurus differed from all other plesiosaurs by having 72 neck vertebrae; more may have been present but were later lost to erosion or after excavation. Only Albertonectes had more neck vertebrae, 76, and the two are the only plesiosaurs with a count higher than 70; more than 60 vertebrae is very derived (or "advanced") for plesiosaurs. [15 ...
See text. Ichthyosauria[ a ] is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of the Mesozoic era; based on fossil evidence, they first appeared around 250 million years ago (Ma) and at least one ...
Liopleurodon (/ ˌlaɪoʊˈplʊərədɒn /; meaning 'smooth-sided teeth') is an extinct genus of carnivorous pliosaurid pliosaurs that lived from the Callovian stage of the Middle Jurassic to the Kimmeridgian stage of the Late Jurassic period (c. 166 to 155 mya). The type species is L. ferox, which is probably the only valid species.
Hydrotherosaurus was a medium-sized plesiosaur, measuring approximately 7.8–8 metres (25.6–26.2 ft) long. [2][3] It has one of the longest necks relative to total length among elasmosaurids, with 60 vertebrae in total. It had a small head that measured about 33 centimetres (13 in; 1.08 ft) long, a streamlined body, and four large flippers ...
The earliest elasmosaurids were mid-sized, about 6 m (20 ft). In the Late Cretaceous, elasmosaurids grew as large as 11.5–12 m (38–39 ft), such as Styxosaurus, Albertonectes, and Thalassomedon. Their necks were the longest of all the plesiosaurs, with anywhere between 32 and 76 (Albertonectes) cervical vertebrae. They weighed up to several ...