New ophthalmosaurid ichthyosaurs from the European lower cretaceous demonstrate extensive ichthyosaur survival across the Jurassic–Cretaceous boundary

Background Ichthyosauria is a diverse clade of marine amniotes that spanned most of the Mesozoic. Until recently, most authors interpreted the fossil record as showing that three major extinction events affected this group during its history: one during the latest Triassic, one at the Jurassic–Cretaceous boundary (JCB), and one (resulting in total extinction) at the Cenomanian-Turonian boundary. The JCB was believed to eradicate most of the peculiar morphotypes found in the Late Jurassic, in favor of apparently less specialized forms in the Cretaceous. However, the record of ichthyosaurs from the Berriasian–Barremian interval is extremely limited, and the effects of the end-Jurassic extinction event on ichthyosaurs remains poorly understood. Methodology/Principal Findings Based on new material from the Hauterivian of England and Germany and on abundant material from the Cambridge Greensand Formation, we name a new ophthalmosaurid, Acamptonectes densus gen. et sp. nov. This taxon shares numerous features with Ophthalmosaurus, a genus now restricted to the Callovian–Berriasian interval. Our phylogenetic analysis indicates that Ophthalmosauridae diverged early in its history into two markedly distinct clades, Ophthalmosaurinae and Platypterygiinae, both of which cross the JCB and persist to the late Albian at least. To evaluate the effect of the JCB extinction event on ichthyosaurs, we calculated cladogenesis, extinction, and survival rates for each stage of the Oxfordian–Barremian interval, under different scenarios. The extinction rate during the JCB never surpasses the background extinction rate for the Oxfordian–Barremian interval and the JCB records one of the highest survival rates of the interval. Conclusions/Significance There is currently no evidence that ichthyosaurs were affected by the JCB extinction event, in contrast to many other marine groups. Ophthalmosaurid ichthyosaurs remained diverse from their rapid radiation in the Middle Jurassic to their total extinction at the beginning of the Late Cretaceous

New data on the ichthyosaur Platypterygius hercynicus and its implications for the validity of the genus

The description of a nearly complete skull from the late Albian of northwestern France reveals previously unknown anatomical features of Platypterygius hercynicus (Kuhn 1946), and of European Cretaceous ichthyosaurs in general. These include a wide frontal forming the anteromedial border of the supratemporal fenestra, a parietal excluded from the parietal foramen, and the likely presence of a squamosal, inferred from a very large and deep facet on the quadratojugal. The absence of a squamosal has been considered as an autapomorphy of the genus Platypterygius for more than ten years and has been applied to all known species by default, but the described specimen casts doubt on this putative autapomorphy. Actually, it is shown that all characters that have been proposed previously as autapomorphic for the genus Platypterygius are either not found in all the species currently referred to this genus, or are also present in other Ophthalmosauridae. Consequently, the genus Platypterygius must be completely revised.Peer reviewe

Morphology and orientation of the ichthyosaurian femur

Orienting ichthyosaur femora, especially in the most derived clade, Ophthalmosauridae, is notoriously problematic (Andrews, 1910; Kirton, 1983; McGowan and Motani, 2003). Structural detachment of the pelvic girdle from the vertebral column early in ichthyosaur evolution (Motani et al., 1998) means that the hind limb is rarely preserved in articulation with other skeletal elements; indeed, in ophthalmosaurids associated hind fins are only reported in Aegirosaurus leptospondylus, Caypullisaurus bonapartei, Ophthalmosaurus icenicus, and Sveltonectes insolitus (Andrews, 1910; Bardet and Fern´andez, 2000; Fern´andez, 2007a; Fischer et al., 2011b). Femora frequently occur in isolation, but even when articulated preservation of the hind paddles precludes unambiguous orientation. There is usually a great deal of morphological and taphonomic variation in the proximal region of the femur (E.M., pers. observ.), which has limited the systematic utility of this element as well as the hind limb more generally. In one of the most widely cited phylogenetic analyses of the Ichthyosauria, 26 characters pertain to the forelimb, whereas only six are drawn from the entire hind limb (Motani, 1999a). The proximal-distal axis of the ichthyosaurian femur is easily identified due to prominent distal facets for articulation with the tibia and fibula and the tendency for the distal end of the femur to be dorsoventrally flattened relative to the proximal end. However, the anterior-posterior and dorsal-ventral axes are much more difficult to differentiate, and are the primary source of controversy (Andrews, 1910; Kirton, 1983; McGowan and Motani, 2003).Erin E. Maxwell, Maria Zammit and Patrick S. Druckenmille

A new Barremian (Early Cretaceous) ichthyosaur from western Russia

A new ophthalmosaurid ichthyosaur, Sveltonectes insolitus gen. et sp. nov., is described from a sub-complete and three-dimensionally preserved specimen from the late Barremian of western Russia. This new taxon is supported by 11 cranial, dental, and postcranial autapomorphies, and is also characterized by features previously considered as autapomorphic for some other Ophthalmosauridae, such as a processus narialis on the prefrontal and relatively long hindfins with pre- and postaxial accessory digits. We conducted a new phylogenetic analysis of Thunnosauria, which supports a ‘Stenopterygius-origin’ for Ophthalmosauridae. Sveltonectes is regarded as the sister taxon of Aegirosaurus, which shares a similar skull roof construction. Contrary to most other Cretaceous ichthyosaurs, Sveltonectes is characterized by delicate and sharply pointed teeth, confirming that the Ophthalmosauridae were ecologically highly diversified during the Early Cretaceou