An ichthyosaur from the Oxfordian–Kimmeridgian of Melville Island, Northwest Territories, Canada, is redescribed. This specimen was previously referred to as Ophthalmosaurus chrisorum Russell, 1993 Romer, A. S. 1968. An ichthyosaur skull from the Cretaceous of Wyoming. Contributions to Geology, 7: 27–41. [Google Scholar] , but exhibits several features incompatible with this generic assignment. Here, I refer this specimen to a new genus, Arthropterygius, characterized by a basioccipital with an extremely reduced extracondylar area, a foramen for the internal carotid artery located on the posterior surface of the basisphenoid, a humerus with a well-developed distal facet for the articulation of a preaxial accessory element, and a radius and ulna with highly angular proximal surfaces for articulation with the humerus. Arthropterygius can be referred to the Ophthalmosauria based on the presence of a preaxial element anterior to the radius and ulna. This referral is supported by a phylogenetic analysis, in which a sister-group relationship between Arthropterygius and the South American genus Caypullisaurus is recovered. This specimen represents the most complete ichthyosaur from the Canadian Arctic, and has important implications for marine reptile diversity at high latitudes during the Jurassic.

Ichthyosaurs remains from the Albian and Cenomanian of Wyoming have been assigned to Platypterygius americanus, but apart from structures of the distal humerus, few other unequivocal character states have been proposed to differentiate this species from its congeners. The purpose of this study was to reevaluate the postcranial morphology of Platypterygius americanus, in order to assess the validity of this species and distinguish postcranial traits relevant for specific diagnoses. Several applicable features were identified, including the location of extrazeugopodial facets on the distal humerus and femur, shape of the intermedium, relative degree of fusion within the atlas-axis complex, number of presacral centra, and varying lengths of the anterior caudal centra. Comparative assessment suggests that Platypterygius americanus is a valid taxon, and that it is possible to differentiate the various Platypterygius spp. independent of stratigraphical and/or geographical occurrence data. Nevertheless, a future review of cranial morphology in all Platypterygius spp. is necessary to bolster these conclusions.

Mesozoic marine reptiles and modern marine mammals are often considered ecological analogs, but the extent of their similarity is largely unknown. Particularly important is the presence/absence of deep-diving suction feeders among Mesozoic marine reptiles because this would indicate the establishment of mesopelagic cephalopod and fish communities in the Mesozoic. A recent study suggested that diverse suction feeders, resembling the extant beaked whales, evolved among ichthyosaurs in the Triassic. However, this hypothesis has not been tested quantitatively. We examined four osteological features of jawed vertebrates that are closely linked to the mechanism of suction feeding, namely hyoid corpus ossification/calcification, hyobranchial apparatus robustness, mandibular bluntness, and mandibular pressure concentration index. Measurements were taken from 18 species of Triassic and Early Jurassic ichthyosaurs, including the presumed suction feeders. Statistical comparisons with extant sharks and marine mammals of known diets suggest that ichthyosaurian hyobranchial bones are significantly more slender than in suction-feeding sharks or cetaceans but similar to those of ram-feeding sharks. Most importantly, an ossified hyoid corpus to which hyoid retractor muscles attach is unknown in all but one ichthyosaur, whereas a strong integration of the ossified corpus and cornua of the hyobranchial apparatus has been identified in the literature as an important feature of suction feeders. Also, ichthyosaurian mandibles do not narrow rapidly to allow high suction pressure concentration within the oral cavity, unlike in beaked whales or sperm whales. In conclusion, it is most likely that Triassic and Early Jurassic ichthyosaurs were ‘ram-feeders’, without any beaked-whale-like suction feeder among them. When combined with the inferred inability for dim-light vision in relevant Triassic ichthyosaurs, the fossil record of ichthyosaurs does not suggest the establishment of modern-style mesopelagic animal communities in the Triassic. This new interpretation matches the fossil record of coleoids, which indicates the absence of soft-bodied deepwater species in the Triassic.

Ichthyosaurs represent one of the most highly specialized lineages of marine reptiles, but our understanding of the evolution of this group is based on specimens found at a surprisingly small number of stratigraphic intervals and localities. The Lower Jurassic (Toarcian) Posidonia Shale of southwestern Germany is one of the richest ichthyosaur-bearing formations in the world and has produced thousands of skeletons, including specimens with preserved soft tissue, and fetal remains inside the body cavity. The most abundant ichthyosaur genus in the Posidonia Shale isStenopterygius. In spite of almost 200 years of research effort, the number of species in this genus is still a point of active disagreement in the literature. Here, bivariate and multivariate analyses are used to classify both articulated and disarticulated skeletons to the level of species, using measurement data from individual cranial and postcranial elements. Unlike previous classification attempts, this technique pinpoints ontogenetically conserved differences in size and proportion between the species, and so can be applied to adult, subadult, and neonatal specimens. Using this method, three species ofStenopterygius, S. quadriscissus, S. triscissus, andS. uniterare differentiated.