Protoichthyosaurus
| Protoichthyosaurus Temporal range: Early Jurassic, | |
|---|---|
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| Paratype skeleton of P. prostaxalis (BRLSI M3553), in Amgueddfa Cymru – Museum Wales | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | †Ichthyosauria |
| Family: | †Ichthyosauridae |
| Genus: | †Protoichthyosaurus Appleby, 1979 |
| Type species | |
| †Protoichthyosaurus prostaxalis Appleby, 1979 | |
| Other species | |
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Protoichthyosaurus is a genus of ichthyosaur from the Early Jurassic of southern England and possibly Switzerland. First described by Robert M. Appleby in 1979, the taxon was regarded as a junior synonym of Ichthyosaurus between 1997 and 2003. Its validity was restored following a revision published in 2017, which identified several anatomical differences, notably in the arrangement and morphology of the carpal bones, as well as the absence of a fifth digit. Two species are currently recognized: the type species P. prostaxalis and P. applebyi, the latter being described in the 2017 revision. However, that same revision removed a third species originally assigned to the genus, P. prosostealis, due to its similarity to Ichthyosaurus. The species most likely lived during the Hettangian stage, but may have lived as early as the Rhaetian and as late as the Sinemurian.
Species belonging to the genus were medium-sized, with P. prostaxalis measuring no more than 2.5 metres (8 ft 2 in) in length and P. applebyi reaching 2 metres (6 ft 7 in) at most. P. prostaxalis can be distinguished from P. applebyi and from other ichthyosaurs by the large, tall, and triangular maxilla that extends beyond the nasal bones at its front end; a vertically short but thick postorbital bone; and the lacrimal bone having an upward projection longer than its forward projection. Meanwhile, P. applebyi can be distinguished by the narrow, crescent-shaped postorbital; the low maxilla; the nasal reaching to the front of the maxilla; the lacrimal having a forward projection the same length as or longer than the upward projection; and the presence of a plate-like upward projection on the humerus.