Ichthyosaurs were a group of predatory marine reptiles which lived from the Lower Triassic (Olenkian) to the Upper Cretaceous (Cenomanian) of the Mesozoic Era. They belong to the clade Ichthyopterygia, which has 80 valid species, and probably reached a cosmopolitan distribution. In the present work, we analyze two ichthyosaurs specimens (MN 1314-V and MN1315-V) preserved in grey silty shales from the Lower Jurassic of Somerset, Southwest England. These materials were one of the first acquisitions of the Paleontological Collection of Museu Nacional/UFRJ during the XIX century. Here, we seek to make the first full morphological description of these samples, as well as establishing their taxonomical positioning through phylogenetic systematics, which has not been done up to date.

The material labeled as MN1315-V consists in a laterally compressed skull, with some of its elements displaced from their original positioning; parts of the pectoral girdle and a partially visible forefin. There are also present elements of the pelvic girdle, two femora, small ribs and vertebrae which make up the apical region of the tail and the inferior lobe of the caudal fin. The ratios taken from the pre-narial and snout regions of the skull in relation to the mandible length, as well as the general width of the snout and the specimen total size (estimated on 1.71m in length), indicate this material belong to the species Ichthyosaurus communis. The forefin exhibit polygonal rather than rounded elements, which are commonly found in the I. communis from Somerset. This allowed us to confirm, also by taxonomical means, the material´s provenance. The material MN1314-V contains mostly non-articulated fragments from different parts of the body, which strongly resemble the ones from the previously mentioned specimen. However, the way in which these were preserved do not allow us to make an objective identification to the generic level, hence being classified as Parvipelvia cf. Ichthyosaurus.

Considering the Ichthyopterygian wide paleobiogeographic distribution until the Lower - Upper Cretaceous boundary, and their probable dispersal routes between Europe, North and South America, the possibility of a future finding of ichthyosaurs in Brazil is persistent. However, to our current knowledge, these are the only ichthyosaur fossil samples which belong to a public paleontological collection in Brazil. This makes these specimens and their analysis not only of didactic and historical importance, but also represent a possible source for future taxonomic or morphological comparisons with any ichthyosaur material to be found in Brazil. Finally, the length of the mandible of MN1315-V, which was indispensable for its species diagnosis, was only able to be accurately measured due to the use of dark light. This simple, but very helpful technique used by us, proved in this study to be of interesting applicability for the taxonomical study of fossil vertebrates.