Plesiosaur phylogeny: revisiting O’Keefe 2001

O’Keefe 2001 analyzed members of the Plesiosauria
(Fig. 1) nesting long-necked Rhomaleosaurus (Fig. 3) with short-necked Kronosaurus (Fig. 3) and long-necked Thalassiodracon was the last common ancestor). O’Keefe also nested short-necked Dolichorhynchops with long-necked Styxosaurus and long-necked Plesiosaurus was a last common ancestor. Why the mix up? Let’s hear from the author himself.

O’Keefe reported,
“Characters from the entire skeleton support these relationships, although characters of the skull roof and palate are especially useful.”

That’s a bold statement falsified by the LRT some twenty years later. Two Hauffiosaurus LRT sisters, Acostasaurus and Anningsaura, known from skulls only, were described after O’Keefe published in 2001, so he can’t be held responsible for those.

The character list
O’Keefe wrote, “The 34 taxa listed above were scored for 166 morphological characters. Of these characters, 107 concerned the skull and 59 were postcranial.”

238 multi-state characters nest taxa in the LRT.

O’Keefe wrote,
“A second analysis was performed with the ‘morphometric’ characters removed, based on the finding that the pliosauromorph body type may have evolved convergently (O’Keefe 2002).”

Note this citation is a year later than O’Keefe 2001. How did he cite a future publication? It was in ‘in press’. Sometimes workers produce more than one paper from a single study.

Not really. If memory serves, plesiosaurs traditionally had small heads and long necks, while pliosaurs traditionally had larger heads and shorter necks. O’Keefe nests long-necked Thalassiodracon (Fig. 3) at the base of the pliosaurs. The LRT nests it with another long-hind-flipper only taxon, Yunguisaurus, not described until 2006.

Muraenosaurus enters the LRT today alongside Rhomaelosaurus.
O’Keefe reported, “The elasmosaur-like long neck and small head evolved independently in Muraenosaurus.”

This is supported by the LRT. Let your cladogram do what you want it to do… nest taxa without bias or preconception.

References
O’Keefe FR 2001. A cladistic analysis and taxonomic revision of the Plesiosauria
(Reptilia: Sauropterygia). Acta Zool. Fennica 213: 1–63.
O’Keefe FR 2002. The evolution and functional morphology of plesiosaur and pliosaur morphotypes inthe Plesiosauria (Reptilia: Sauropterygia). — Paleobiology 28(1). [In press at the time in 2001].