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Ichthyosaurus anningae, new species from Lower Jurassic of West Dorset, England

Ben Creisler

A new online paper:

Dean R. Lomax & Judy A. Massare (2015)
A new species of Ichthyosaurus from the Lower Jurassic of West Dorset,
England, U.K.
Journal of Vertebrate Paleontology (advance online publication)

We describe a new species of Lower Jurassic
(Hettangian/Sinemurian–Pliensbachian) ichthyosaur, Ichthyosaurus
anningae, sp. nov., from west Dorset, England, U.K. The holotype of I.
anningae (DONMG:1983.98), at least a subadult, is from the lower
Pliensbachian Stonebarrow Marl Member (Charmouth Mudstone Formation).
It is the most complete ichthyosaur known from this time interval
worldwide. The species is assigned to Ichthyosaurus on the basis of
humerus, forefin, and pectoral girdle morphologies. Diagnostic
features of the species include a short, robust humerus with prominent
processes; a femur in which the proximal width is almost as large as
the distal width; and a very small femur relative to the humerus
(humerus/femur ratio >1.7). Four other specimens, at least three of
which are juveniles, are referred to this species. The new species may
display sexual dimorphism in humeral morphology, but this cannot be
confirmed due to a lack of stratigraphic information. With the
recognition of I. anningae, at least three and possibly as many as
five ichthyosaur species, representing three genera, are known from
the Pliensbachian.