Eretmosaurus

Eretmosaurus (meaning "oar lizard") is an extinct genus of plesiosaur from the Early and Middle Jurassic of England and Russia. Two species are known: E. rugosus and E. dubius.

History

Eretmosaurus rugosus

The holotype of E. rugosus has no known recorded specimen number and it consists of vertebrae, girdles, and limb bones discovered in Granby, Nottinghamshire where the Asteroceras obtusum zone of the Lower Lias Formation outcrops.

Specimen BRSMB Cb 2458 was also assigned to the species by Owen (1840). This specimen later became the syntype and it consisted of several vertebrae that had been discovered at different locations in the Blue Lias Formation in Gloucestershire across Aust Cliff.

Owen (1840) was the first to describe the specimens, which were named as Plesiosaurus rugosus.R. Owen. (1840). Report on British fossil reptiles. Report of the Ninth Meeting of the British Association for the Advancement of Science, Reports on the State of Science 43-126 Later, Owen (1865) described a headless skeleton discovered in the Ammonites stellaris zone of the Blue Lias at Granby, Nottinghamshire (NHMUK 14435) that he assigned to P. rugosus,R. Owen. (1865). A monograph of the fossil Reptilia of the Liassic formations. Part I, Sauropterygia. Palaeontographical Society Monographs 17(75):1-40 and Seeley used NHMUK 14435 as the basis for naming Eretmosaurus rugosus in 1874.Seeley, H. G., (1874), Note on some of the generic modifications of the plesiosaurian pectoral arch: Quarterly Journal of the Geological Society of London, 1874, p. 436-449.

As BRSMB Cb 2458 was not diagnostic and was lost by 1940, a petition was filed with the ICZN over the holotype by Brown and Bardet (1994),David S. Brown and Nathalie Bardet (1994). Plesiosaurus rugosus Owen, 1840 (currently Eretmosaurus rugosus, Reptilia, Plesiosauria) proposed designation of a neotype. Bulletin of Zoological Nomenclature 51(3) and NHMUK 14435 was allocated as the official neotype in 1996.David S. Brown and Nathalie Bardet (1996). Plesiosaurus rugosus Owen, 1840 (currently Eretmosaurus rugosus, Reptilia, Plesiosauria) neotype designated. Bulletin of Zoological Nomenclature 53(1)

A fragmentary specimen of Eretmosaurus rugosus has also been identified from the Middle Jurassic of Siberia by Menner (1992).

Eretmosaurus dubius A partial skull and skeleton belonging to a plesiosaur was discovered in the Harpoceras faleifer zone, Whitby, England and it was initially described by Blake & Tate (1876) as a species of Plesiosaurus known as P. dubius. It was later reclassified as a species of Eretmosaurus by Blake in Blake & Tate (1876).

Other species Benton and Spencer (1995) mentioned a third species of Eretmosaurus: E. macropterus; they rectified this mistake within the same paper by mentioning on page 116 that E. macropterus actually belongs to Microcleidus.Benton, M. J. and Spencer, P. S. (1995). Fossil reptiles of Great Britain. Chapman and Hall, London, 386 pp.

Classification Eretmosaurus was classified into Rhomaleosauridae by Persson (1963),Persson, P.O. (1963): A revision of the classification of the Plesiosauria, with a synopsis of the stratigraphical and geographical distribution of the group. University of Lunds Årsskrift 59, No. 1, p. 1-57. then into Pliosauridae by Brown (1981),Brown, D. S. (1981). The English Upper Jurassic Plesiosauroidea (Reptilia) and a review of the phylogeny and classification of the Plesiosauria. Bulletin of the British Museum (Natural History): Geology, 35, (4), 253-347. then into Elasmosauridae by Bardet (1995)Bardet, N. (1995). Evolution et extinction des reptiles marins au cours du Mésozoïque. Palaeovertebrata, 24, 177-283. and Bardet et al. (1999),Bardet, N.; Godefroit, P.; and Sciau, J. (1999). A new elasmosaurid plesiosaur from the Lower Jurassic of Southern France. Palaeontology, 42, (5), 927-952. and most recently into Microcleididae by Benson et al. (2012).

Eretmosaurus

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