Two new plesiosaur species and new data on Brachauchenius

The most recent Journal of Vertebrate Palaeontology (Volume 27(1)) contains three new plesiosaur papers. A short communication by Ben Kear (p. 241-246) clarifies the taxonomy of what has become a very confusing taxon – Eromangasaurus. The confusion originated because two separate researchers (Ben Kear and Sven Sachs) published separate descriptions and names for the same specimen, simultaneously. The officially settled name of this taxon is Eromangasaurus australis (Sachs, 2005) Kear, 2005

The other two articles form part 1 and part 2 of a review of plesiosaurs from the Upper Cretaceous Tropic Shale of southern Utah by Albright et al. (2007)

The first part (p.31-40) describes new material pertaining to Brachauchenius lucasi. Interestingly, I was surprised to see an infamous historical blunder rear its head. In 1957 Tarlo described an unusual pliosaur scapula and introduced the new genus Stretosaurus based on its unique morphology. Despite this interpretation being perpetuated in later papers (Tarlo 1959, 1960), Tarlo (who changed his name to Halstead) later pointed out (1989) that this unique scapula was in fact a perfectly normal pliosaur ilium. In their new paper, Albright et al present two possible reconstructions for the partial scapula of Brachauchenius, one based on Liopleurodon, the other based on the ‘Stretosaurus’ ilium (Fig. 1). I’m surprised this error made it through the peer review process.

Brachauchenius scapula
Fig 1. The two interpretations proposed by Albright et al for the partial scapula of Brachauchenius. ‘A’ is based in the ilium of ‘Stretosaurus’, erroneously identified as a scapula by Tarlo (1957). From Albright et al (2007).

It is also possible that both interpretations of the pelvic girdle (Fig. 2) given by Albright et al are erroneous. Comparison with other specimens of Brachauchenius overlooked by the authors (Fig. 3) and other pliosaurs (Figs. 4, 5) show that the pelvic girdle is always greatly elongate in pliosaurs. Although it is not possible to be certain without observing the specimen first hand, it appears that the orientation of at least some of the elements in Fig. 2  are open to reinterpretaion. Likely, the margin interpreteted as the obturator foramen is the lateral margin of the pubis. It is also possible that the pubis and coracoid have been muddled up.

Brachauchenius girdle
Fig. 2. The two proposed interpretations of one half of the pelvic girdle of Brachauchenius. From Albright et al. (2007)

Hampe pubis
Fig 3. Pubis of a specimen of Brachauchenius sp., as figured by Hampe (2005). Anterior towards the top – the orientation is confident because the specimen is articulated. This paper was overlooked by Albright et al (2007)

Liopleurodon pelvic girdle
Fig 4. Pelvic girdle of Liopleurodon, showing the greatly elongated form typical of pliosaurs. from Andrews (1913)

Simolestes pelvic girdle
Fig 5. Pelvic girdle of Simoletes, again showing the greatly elongated form typical of pliosaurs. from Andrews (1913)

The second paper in this two-parter (p. 41-58) introduces two new genera and species (Palmula quadratus and Eopolycotylus rankini), plus two new subfamilies within polycotylid plesiosaurs – Palmulainae and Polycotylinae. I may comment on this in the future.

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