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Acamptonectes, new ichthyosaur in PLoS ONE



From: Ben Creisler
bscreisler@usc.edu
 
A new marine reptile paper in PLoS ONE:
 
 Valentin Fischer, Michael W. Maisch, Darren Naish, Ralf Kosma, Jeff Liston, 
Ulrich Joger, Fritz J. Krüger, Judith Pardo Pérez, Jessica Tainsh & Robert M. 
Appleby (2012)
New Ophthalmosaurid Ichthyosaurs from the European Lower Cretaceous Demonstrate 
Extensive Ichthyosaur Survival across the Jurassic–Cretaceous Boundary. 
PLoS ONE 7(1): e29234. 
doi:10.1371/journal.pone.0029234
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0029234
 
 
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 Oxfordia
t 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.