A new species of Ichthyosaurus from the Lower Jurassic of West Dorset, England, U.K.

ABSTRACT

We describe a new species of Lower Jurassic (Hettangian/Sinemurian–Pliensbachian) ichthyosaur, Ichthyosaurus anningae, sp. nov., from west Dorset, England, U.K. The holotype of I. anningae (DONMG:1983.98), at least a subadult, is from the lower Pliensbachian Stonebarrow Marl Member (Charmouth Mudstone Formation). It is the most complete ichthyosaur known from this time interval worldwide. The species is assigned to Ichthyosaurus on the basis of humerus, forefin, and pectoral girdle morphologies. Diagnostic features of the species include a short, robust humerus with prominent processes; a femur in which the proximal width is almost as large as the distal width; and a very small femur relative to the humerus (humerus/femur ratio >1.7). Four other specimens, at least three of which are juveniles, are referred to this species. The new species may display sexual dimorphism in humeral morphology, but this cannot be confirmed due to a lack of stratigraphic information. With the recognition of I. anningae, at least three and possibly as many as five ichthyosaur species, representing three genera, are known from the Pliensbachian.

http://zoobank.org/urn:lsid:zoobank.org:pub:A5778FB5-A116-480A-93CA-AFC932ACAB55

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ACKNOWLEDGMENTS

We thank Doncaster Museum Service for allowing the study of the specimen, and P. Robinson for providing access. The specimen was purchased with the help of a grant from the PRISM fund (Museums Libraries and Archives). We also thank S. Chapman and P. Barrett (NHMUK), C. Howells (NMW), M. Riley and S. Finney (CAMSM), E. Howlett (OUMNH), D. Parsons and Somerset Heritage Service (MOS), E. Daeschler and E. Gilmore (ANSP), R. Vaughan (BRSMG), P. Shepherd and L. Neep (BGS), and M. Evans (LEICT) for access to and help with specimens. E. Hall and R. Davies produced the interpretative illustrations. N. Larkin uncovered background information on DONMG:1983.98 and did additional preparation of the specimen. The preparation and a portion of D.R.L.'s research costs were funded by the Esmée Fairbairn Foundation (CIRCA project), as part of a grant awarded from the Museums and Heritage Strand to Doncaster Museum Service. D.R.L. would also like to thank the Western Interior Paleontological Society for a Karl Hirsch Memorial Grant, which partially funded research costs. J.A.M.'s travel expenses were partially funded by a Scholarly Incentive Grant and a Faculty Research Grant from SUNY Brockport. Thanks to E. Maxwell, P. Druckenmiller, W. Wahl, and S. Stouge for their helpful suggestions and comments.