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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 ...
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 ...
Pliosauridae is a stem-based taxon defined in 2010 (and in earlier studies in a similar manner) as "all taxa more closely related to Pliosaurus brachydeirus than to Leptocleidus superstes, Polycotylus latipinnis or Meyerasaurus victor ". [1] The family Brachauchenidae has been proposed to include pliosauroids which have very short necks and may ...
Most European species of Pliosaurus measured around 8 metres (26 ft) long and weighed about 5 metric tons (5.5 short tons), but P. rossicus and P. funkei would have been one of the largest plesiosaurs of all time, exceeding 10 metres (33 ft) in length.
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.
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 ...
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 ...