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A previously unrecognized specimen of Protoichthyosaurus prostaxalis , LEICT G142.1991, from the Lower Jurassic of Barrow-upon-Soar, Leicestershire, UK, includes an almost complete three-dimensional skull that provides new information on the configuration of the skull roof. The position of the pineal foramen (between the frontals and the parietals) and an elongated internasal foramen in a depression along the midline of the nasals are clearly shown. The maxilla makes up a significant portion of the external naris ventral margin, an unusual character for the genus/species. This reflects intraspecific variation, not evidence of a new taxon. The specimen enables comparisons of skull roof morphology with Ichthyosaurus and Stenopterygius , two common Early Jurassic taxa. In particular, the position of the pineal foramen is similar to Stenopterygius , but distinguishes Protoichthyosaurus from Ichthyosaurus. The lack of a frontal–prefrontal contact and the posteriorly wide nasals distinguishes Protoichthyosaurus from Stenopterygius. We also present a revised reconstruction of the skull roof morphology of Ichthyosaurus. Three additional specimens of Protoichthyosaurus are referred to the genus: another partial skull, referred to P. prostaxalis , and two isolated forefins, identified by their unique morphology. [ABSTRACT FROM AUTHOR]

The abundance of specimens of Ichthyosaurus provides an opportunity to assess morphological variation without the limits of a small sample size. This research evaluates the variation and taxonomic utility of hindfin morphology. Two seemingly distinct morphotypes of the mesopodium occur in the genus. Morphotype 1 has three elements in the third row: metatarsal two, distal tarsal three and distal tarsal four. This is the common morphology in Ichthyosaurus breviceps , I. conybeari and I. somersetensis. Morphotype 2 has four elements in the third row, owing to a bifurcation. This morphotype occurs in at least some specimens of each species, but it has several variations distinguished by the extent of contact of elements in the third row with the astragalus. Two specimens display a different morphotype in each fin, suggesting that the difference reflects individual variation. In Ichthyosaurus , the hindfin is taxonomically useful at the genus level, but species cannot be identified unequivocally from a well-preserved hindfin, although certain morphologies are more common in certain species than others. The large sample size filled in morphological gaps between what initially appeared to be taxonomically distinct characters. The full picture of variation would have been obscured with a small sample size. Furthermore, we have found several unusual morphologies which, in isolation, could have been mistaken for new taxa. Thus, one must be cautious when describing new species or genera on the basis of limited material, such as isolated fins and fragmentary specimens. [ABSTRACT FROM AUTHOR]

Ichthyosaurus communisDe la Beche & Conybeare, 1821 andI. intermediusConybeare, 1822 have been considered synonymous by some researchers, but distinct species by others. The distinction between the two species was originally based on tooth morphology, which has been shown to vary ontogenetically as well as within an individual. Subsequent literature of the nineteenth century did not propose adequate diagnostic features to distinguish the two species. In addition, illustrations suggest that both species were confused withI. breviceps, which was defined over 50 years later. The type specimens of both species are missing, making the problem unresolvable. However, a neotype was designated forI. communisto retain the widely used species name and to stabilize the taxonomy. The species can be recognized by a symmetric, triangular maxilla with long processes and a large, broad, triradiate lacrimal, as well as a unique combination of other characters. The neotype shares numerous features with theI. intermedius ‘type figure’, including the morphologies of the maxilla, prefrontal, lacrimal, jugal and postorbital, such that the two are nearly indistinguishable. ThusI. intermediusmust be considered a synonym ofI. communis.Ichthyosaurus communiscan be identified from the Lyme Regis-Charmouth coast, west Dorset; the ?Whitby coast of Yorkshire; and probably from Street, Somerset. The stratigraphical range ofI. communisis at least lower Hettangian to lower Sinemurian. [ABSTRACT FROM PUBLISHER]

ABSTRACT—Ichthyosaurus conybeariis a rare species, previously known only from an incomplete holotype and one referred specimen, both from the Lyme Regis area of the west Dorset coast, U. K. A newly recognized, nearly complete specimen (NMW 93.5G.2) is the first occurrence of the species in Somerset, U. K. A revised diagnosis recognizes new morphological characters that distinguish the species: slender maxilla with a long, delicate premaxillary process; narrow postorbital; humerus with an anteriorly offset dorsal process that has a well-defined lip extending slightly into the shaft; fibula that is much larger dorsoventrally and mediodistally than tibia; and wide rectangular ischium that is much shorter than the pubis and femur. Notching of anterior fin elements in the forefin had been used as a diagnostic character, but a review of notching withinIchthyosaurussuggests that it has little taxonomic utility. Another specimen (NHMUK R15907), herein referred to the species, extends the range ofI. conybearifrom the upper Hettangian to lower Pliensbachian stages of the Lower Jurassic, the longest duration of any species of the genus. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free atwww.tandfonline.com/UJVP Citation for this article: Massare, J. A., and D. R. Lomax. 2016. A new specimen ofIchthyosaurus conybeari(Reptilia, Ichthyosauria) from Watchet, Somerset, England, U.K., and a reexamination of the species. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1163264. [ABSTRACT FROM PUBLISHER]