New ophthalmosaurid ichthyosaurs from the European Lower Cretaceous demonstrate extensive ichthyosaur survival across the Jurassic-Cretaceous boundary

• Published in: PloS one Vol. 7; no. 1; p. e29234
• Main Authors: Fischer, Valentin, Maisch, Michael W, Naish, Darren, Kosma, Ralf, Liston, Jeff, Joger, Ulrich, Krüger, Fritz J, Pérez, Judith Pardo, Tainsh, Jessica, Appleby, Robert M
• Format: Journal Article Web Resource
• Language: English
• Published: United States Public Library of Science 03.01.2012; Public Library of Science (PLoS)
• Subjects: Acamptonectes densus; Analysis; Animals; Art galleries & museums; Autobiographies; Biology; Cladistic analysis; Cretaceous; Cretaceous period; Earth science; Earth Sciences; Earth sciences & physical geography; Endangered & extinct species; Endangered species; Europe; Evolution, Molecular; Evolutionary biology; Extinction; Extinction, Biological; Fossils; Geography; Geology; Greensand formation; Hauterivian; Ichthyopterygia; Ichthyosauria; Ichthyosaurs; Jurassic; Jurassic period; Jurassic–Cretaceous boundary; Life sciences; Mass extinction; Mass extinctions; Mesozoic; Morphology; New species; Ophthalmosauridae; Ophthalmosaurinae; Paleontology; Phylogeny; Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; Platypterygiinae; Radiation; Reptiles - anatomy & histology; Reptiles - genetics; Reptiles - physiology; Reptilia; Sciences de la terre & géographie physique; Sediments; Species extinction; Survival; Survival rate; Taxa; Triassic; Europe; Glasgow Scotland; United Kingdom > UK; Queensland Australia; Wyoming; United States > US; Scotland; North America; Russia; Canada; Belgium; Australia; Germany
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0029234

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. 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. 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.