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Acamptonectes, new ichthyosaur in PLoS ONE
From: Ben Creisler
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.
New Ophthalmosaurid Ichthyosaurs from the European Lower Cretaceous Demonstrate
Extensive Ichthyosaur Survival across the Jurassic–Cretaceous Boundary.
PLoS ONE 7(1): e29234.
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 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.
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.