The first known neonate Ichthyosaurus communis skeleton: a rediscovered specimen from the Lower Jurassic, UK.

Numerous specimens of Ichthyosaurus are known, but only very few small examples (total length of <1 m) have been assigned beyond Ichthyosaurus sp. Here, we report on a very small specimen (preflexural length of 560 mm) that can be unequivocally assigned to Ichthyosaurus communis due to possessing a unique combination of diagnostic skull and postcranial characters that are found in larger examples of the species. Furthermore, the specimen is identified as a neonate because of the small size, large sclerotic ring relative to the orbital region, and poorly ossified (highly cancellous) bones of the skull and postcranium. It is not an embryo as it is not preserved within an adult specimen and stomach contents are clearly evident. This is therefore the first neonate Ichthyosaurus communis skeleton to be described. The specimen, in the Lapworth Museum of Geology, University of Birmingham, has no provenance data associated with it. A microfossil analysis of the matrix in which the ichthyosaur skeleton is preserved strongly suggests a stratigraphic range of uppermost Hettangian to lowermost Sinemurian age (Lower Jurassic), but does not provide any geographical information. [ABSTRACT FROM AUTHOR]