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A new global phylogeny of Plesiosauria (Reptilia: Sauropterygia)
SVPCA Conference
Platform presentation (20 minutes)
*Kilary Ketchum
Plesiosauria was a diverse clade of predatory marine reptiles secondarily adapted to life in water, that played an important role in Mesozoic marine ecosystems. A new hypothesis of the phylogeny of Plesiosauria is presented that incorporates 64 taxa scored for 175 new and critically re-examined morphological characters, the majority of which are based on personal examination of relevant specimens, making it the largest and most comprehensive cladistic analysis of Plesiosauria to date.

The strict component consensus tree of the 18 most parsimonious trees recovered by the parsimony analysis is well resolved, and removal of only three ‘wildcard’ taxa by reduced consensus methods results in a fully resolved reduced consensus tree; however, bootstrap proportions and Bremer support indices for the majority of ingroup relationships are low. In agreement with some previous analyses (e.g. O’Keefe, 2001) but in contrast to Druckenmiller and Russell (2006), the present analysis does not support the traditional hypothesis of a simple dichotomy between taxa with long necks and small heads (‘plesiosaurs’) and those with short necks and large heads (‘pliosaurs’), which had dominated pre-cladistic taxonomy for over 100 years. Instead, the large headed, short-necked clade, Polycotylidae, is more closely related to Plesiosaurus dolichodeirus than to Pliosaurus brachydeirus. However, the recovered topology differs in many important respects from those generated by previous analyses, in particular in the relationships of the more basal taxa, which necessitates re-definition of a number of clades to produce a stable phylogenetic taxonomy.

London 2020