Until very recently the taxonomy within sauropterygia has been in disarray, despite a widespread early interest in the group (Rieppel, 1997). Interrelationships were drawn based largely upon skull-less specimens (Weller, 1962 and White 1940 in Carpenter, 1997) and undiagnostic features such as neck length and head size (Carpenter, 1997) and many taxa have been shoehorned into wastebasket genera such as Plesiosaurus of which there are hundereds of species, mostly undiagnostic or unique genera, known worldwide. This long history of Sauropterygian study is actually a hinderence to our current understanding. Many characters are also yet to be confirmed for all members of clades because of poor quality material (Sues, 1986). As a result there are numerous synonyms, for example, Tarlo (1960) winnowed 19 pliosaurs down to 7 . In the Plesiosauria the constant proportions of the body between taxa may have served as a reason to classify based on neck length (Carroll, 1988). The absence of articulated remains in the Triassic (Carroll, 1988; Storrs, 1993) limits our knowledge of the "nothosaur"- plesiosaur transition.
Classification of plesiosaurs is currently under revision (Carpenter, 1997; Rieppel, 1997; Bakker, 1993; O'keefe, 2001). Traditional plesiosaur phylogenies comprise four main families: Pliosaurids, Plesiosaurids, Cryptoclidids and Elasmosaurids (Brown, 1981), regarded the Jurassic and Cretaceous a time of evolutionary continuity. This is an artefact of the traditional classification based on neck length (Bakker 1993). There have been numerous convergencies and extinctions as Bakker (1993) has identified and as such it is especially important to distinguish between, as Bakker (1993) terms it, 'heritage and habitus'. The post-crania is shaped by ecological need and thus its evolution is conservative (Carpenter, 1997). Except for elongation of the snout (Carpenter, 1997) and perhaps supporting structures (Forrest pers. comm. 2002), the skull is less effected by parameters of ecology. Based on evidence of the skull, short necked plesiosaurs such as Dolichorhynchops osborni have been recently reclassified as polycotylids, related closely to elasmosaurids rather than being pliosaurs (Carpenter 1997). Indeed, cladistic analyses (O'keefe, 2001) seem to confirm this. Plesiosaur evolution is more complicated than previously acknowledged.