Correction: New Ophthalmosaurid Ichthyosaurs from the European Lower Cretaceous Demonstrate Extensive Ichthyosaur Survival across the Jurassic–Cretaceous Boundary

Abstract

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.

A large new Middle Jurassic ichthyosaur shows the importance of body size evolution in the origin of the Ophthalmosauria

“…australis and Baptanodon [ 16 , 38 , 65 ]. The exoccipital remains tall as in Baptanodon and O. icenicus rather than squat as in Acamptonectes [ 16 , 32 , 65 ]. The ventrally directed basioccipital facet is very rugose and contains grooves, potentially indicating a larger cartilaginous contact between the exoccipital and the basioccipital (Fig.…”

“…The v-shaped morphology is common in ophthalmosaurians with some notable exceptions in which the impression of the sacculus is expanded ( Pl. australis, Sisteronia and Acamptonectes , which has a distinct ventral bulge holding the sacculus [ 32 , 38 , 64 ]).…”

“…O. icenicus , Stenopterygius and Ar. hoybergeti [ 16 , 61 , 62 ]; Acamptonectes comes closest in quadrangular shape [ 32 ]. The supraoccipital contributes substantially to the foramen magnum, roughly 50% of the height of the foramen.…”

“…Nutritive foramina are sporadically present in euichthyosaurs throughout phylogeny, e.g. Ichthyosaurus , Temnodontosaurus , Acamptonectes and O. icenicus [ 16 , 32 , 50 , 69 ]. The most striking feature of the supraoccipital of PIMUZ A/III 5279 is the anteroposterior elongation of the exoccipital processes, seen in lateral and ventral view (Fig.…”

“…The otic capsule impression is directed anterolaterally and shows a triradiate morphology, different from some ophthalmosaurians such as Sisteronia, and Pl. hercynicus which show an almost lunate capsular impression [ 32 ], 2014), but similar to e.g. Pl.…”