Eretmosaurus (Owen, 1865)

Classification

Sauropterygia > Eosauropterygia > Eusauropterygia > Pistosauroidea > Plesiosauria >Plesiosauria incertae sedis

Species

Eretmosaurus rugosus (Owen, 1865) (Type and only species)

Material

BMNH 14435, almost complete skeleton with skull missing, almost complete vertebral column and associated ribs, complete pectoral girdle poorly exposed and complete pelvic girdle with all four limbs complete and in articulation.

Distribution

Ammonites stellaris zone, Sinemurian, Lower Jurassic, Granby, Leicestershire (further detail is unavailable).

Images

Specimen BMNH 14435, the Neotype of Eretmosaurus rugosus

Photograph of BMNH 14435 on display in the NHM, London. Because these specimens are wall mounded and covered in glass, they are unfortunately very difficult to see, let alone investigate scientifically. Photo by Chris Crump, used with kind permission.

Discussion

Genus named for 'Plesiosaurus' rugosus by Seeley (1874). Eretmosaurus is something of a rogue taxon, workers have been in disagreement as to the taxonomic affinities of Eretmosaurus and it has been included in:

Rhomaleosauridae, based on the girdle bones according to Persson (1963).
Pliosauridae according to Brown (1981).
Elasmosauridae according to Bardet (1995) and Bardet et al. (1999).

The latter two authors give no specific justification for their diagnoses. Furthermore, the holotype lacks a head so the rogue nature of Eretmosaurus can be confidently attributed to abundant missing data (Wilkinson, 1995). This hints that postcranial characters may be unreliable. In my cladistic analysis, reduced consensus methods (Thorley and Page, 2000) removed Eretmosaurus in two of three reduced trees and strict consensus of heuristic searches minus Eretmosaurus, were more resolved. Eretmosaurus, last described by Owen (1865), is referred to Plesiosauria incertae sedis pending revision of this taxon and/or the discovery of more complete, especially cranial material.

After confusion over the type material of this species, a formal petition was filed with the ICZN (Brown and Bardet, 1994). The skeleton described here (BMNH 14435) is the official holotype. In a case of mistaken identity, Benton and Spencer (1995) discuss Eretmosaurus macropterus, (e.g. pp.115, 120) but this is actually a species of Microcleidus as correctly pointed out on p. 116 (ibid).