Editing Plesiosaurus (section)

===Skull and dentition===

[[File:Plesiosaurus Scale.svg|thumb|''Plesiosaurus'' with a human to scale.]]
Compared to other plesiosaur genera, ''Plesiosaurus'' has a small head. The skull is much narrower than long,<ref name=Storrs166>Storrs 1997 pp. 166</ref> reaching its greatest width just behind the eyes (the [[postorbital]] bar).<ref name=Storrs165>Storrs 1997 pp. 165</ref> The [[anatomical terms of location|anterior]] portion is "bluntly triangular".<ref name=Storrs165/> In lateral view, the skull reaches its highest point at the rear of the [[skull roof|skull table]].<ref name=Storrs167>Storrs 1997 pp. 167</ref> "The external nostrils overlie the internal nares".<ref name=Storrs165/> They are not positioned at the tip of the snout, but farther back, nearer the eyes than the tip of the skull.<ref name=Storrs166/> Unlike the nostrils of ''[[Rhomaleosaurus]]'',<ref>Cruickshank 1991</ref> they do not appear to be adapted for underwater olfaction.<ref name=Storrs165/> The [[orbit (anatomy)|orbits]] (eye sockets) are roughly circular and are positioned about halfway along the length of the skull.<ref name=Storrs165/> They face up and to the sides.<ref name=Storrs166/><ref name=Storrs167/> Just posterior to the orbits are the [[supratemporal fenestra]]e, which are about the same size as the orbits and also roughly circular.<ref name=Storrs165/> Between the four openings is the [[Pineal gland#Miscellaneous anatomy|pineal foramen]], and between the temporal fenestrae is a narrow sagittal ridge.<ref name=Storrs165/> As in other plesiosaurs, the [[Pterygoid bone|pterygoid]]s of the palate are fused to the [[Occipital bone#In other animals|basioccipital]] of the [[braincase]],<ref name=Storrs165/> although the union is not as robust as in the pliosaurs ''Rhomaleosaurus'' and ''[[Pliosaurus]]''.<ref name=Storrs165/><ref>Taylor and Cruickshank 1993</ref> "The palatal bones are thin, but there is no suborbital fenestra."<ref name=Storrs165/>

The two [[ramus of the mandible|rami of the lower jaw]] make a "V" shape with an angle of about 45°.<ref name=Storrs166/> The specialized region where they meet, the [[Symphysis menti|symphysis]], is robust. The two rami are fused at the symphysis, making a pointed, shallow scoop-like shape.<ref name=Storrs169>Storrs 1997 pp. 169.</ref>

The teeth of ''Plesiosaurus'' are "simple, needle-like cones" that are "slightly curved and circular in transverse section". They are sharply pointed with fine striations running from tip to base, and point forward (procumbent). This procumbency becomes more pronounced near the leading end of the skull, where they may be only 10–15° above horizontal.<ref name=Storrs166/> There are 20 to 25 teeth per upper jaw tooth row,<ref name=Storrs165/> and 24 per low jaw tooth row.<ref name=Storrs166/> Up to four teeth of a lower jaw's tooth row are found in the symphyseal region.<ref name=Storrs169/>