Abstract

An ichthyosaur in the collections of the Sedgwick Museum, Cambridge (CAMSMX.50187) was collected in the nineteenth century by the renowned fossil collector Mary Anning, but has never been adequately described in the literature. As an Anning specimen, it is certainly from the Lower Jurassic of Lyme Regis, west Dorset. The near complete presacral skeleton is lying on its left side and includes a complete skull, one complete and one partial forefin, pectoral bones, all six elements of the pelvic girdle, and both hindfins. The centra in the anterior caudal region, however, are from another individual and may have replaced the original ones. The specimen is identified as Ichthyosaurus based on the morphology of the humerus and forefin. It is assigned to I. breviceps on the basis of the relatively short snout, large eye, and tall neural spines. This is the only known specimen of I. breviceps to preserve a complete pelvis. Notably, the ilium is longer than the pubis and ischium, and the pubis is longer than the ischium. This individual is the largest I. breviceps reported in the literature, with jaw length of 33.5 cm and estimated length from snout to tail bend of 1.6 m.

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