page_title: Plesiosaurus
section_title: Vertebral column
hierarchical_section_title: Plesiosaurus / Description / Vertebral column
caption_attribution_description: English: Illustration of the skeletal anatomy of a Plesiosaurus dolichodeirus from Conybeare's 1824 paper that described an almost complete plesiosaur skeletion found by Mary Anning in 1823
context_page_description: Plesiosaurus is a genus of extinct, large marine sauropterygian reptile that lived during the early part of the Jurassic Period, and is known by nearly complete skeletons from the Lias of England. It is distinguishable by its small head, long and slender neck, broad turtle-like body, a short tail, and two pairs of large, elongated paddles. It lends its name to the order Plesiosauria, of which it is an early, but fairly typical member. It contains only one species, the type, Plesiosaurus dolichodeirus. Other species once assigned to this genus, including P. brachypterygius, P. guilielmiiperatoris, and P. tournemirensis have been reassigned to new genera, such as Hydrorion, Seeleyosaurus and Occitanosaurus.
context_section_description: Plesiosaurus was a moderately sized plesiosaur that grew to a length of about 3.5 metres (11 ft). There are approximately 40 cervical vertebrae (neck vertebrae), with different specimens preserving 38 to 42 cervical vertebrae.  Of the rest of the vertebral column, there are a handful (four or five in the holotype specimen) of "pectoral" vertebrae from the neck-torso transition, approximately 21 dorsal or back vertebrae, three or more sacral vertebrae, and at least 28 caudal vertebrae. Generally, the centra of the cervical vertebrae are relatively elongated, being slightly longer than tall. The width, however, is usually greater than or equal to the length. The articular surfaces of the cervical centra are "slightly concave and kidney-shaped, with rounded, slightly rugose edges." Small holes called foramina subcentralia are found on the ventral surface of the centra. Some of the dorsals have rugose articular edges, like the cervicals; this feature is typically absent from the caudals.
  Ribs are found from the neck to the tail. Cervical ribs are hatchet-shaped and have two articular heads. Dorsal ribs are thick and have only one head. Sacral ribs are "short, robust, and blunt or knob-like on both ends." Caudal ribs have different morphologies depending on their location along the tail, with anterior examples being pointed and more distal examples being "broad and blunt." Plesiosaurus also has gastralia, also known as "belly ribs." Nine or more sets of gastralia are present between the shoulder and pelvis. Each set is composed of seven elements: a bone on the midline flanked by three lateral elements.
caption: Illustration of the skeletal anatomy of a Plesiosaurus dolichodeirus from Conybeare's 1824 paper that described an almost complete plesiosaur skeleton found by Mary Anning in 1823
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