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Ophthalmosaurid ichthyosaur from Jurassic of Alaska



From: Ben Creisler
bcreisler@gmail.com


A new online paper:

Patrick S. Druckenmiller & Erin E. Maxwell (2013)
A Middle Jurassic (Bajocian) ophthalmosaurid (Reptilia, Ichthyosauria)
from the Tuxedni Formation, Alaska and the early diversification of
the clade.
Geology Magazine (advance online publication)
DOI: http://dx.doi.org/10.1017/S0016756813000125
http://128.232.233.5/action/displayAbstract?fromPage=online&aid=8874248&fulltextType=RA&fileId=S0016756813000125

Ophthalmosauridae is a clade of derived thunniform ichthyosaurs that
are best known from Callovian (late Middle Jurassic) to
Cenomanian-aged (Late Cretaceous) deposits in both the Northern and
Southern Hemispheres. Ophthalmosaurids arose prior to the Early–Middle
Jurassic boundary, however, very little is known about their diversity
and distribution in the earliest phase of their evolutionary history
during the Aalenian–Bathonian (Middle Jurassic) interval. Here we
describe new diagnostic ophthalmosaurid material from the Early
Bajocian (Middle Jurassic) of Alaska. The specimen, UAMES 3411, is a
partial disarticulated skull that was discovered in the Middle
Jurassic Tuxedni Formation, which was deposited in shallow marine
settings outboard of the then-accreting Wrangellia composite terrane.
The new material is significant in that it is the first Jurassic
ichthyosaur described from Alaska, one of the oldest ophthalmosaurids
known and the only Middle Jurassic ophthalmosaurid described from the
Northern Hemisphere. The new material adds to a rapidly growing data
set on ophthalmosaurid diversity and suggests that the clade was
geographically widespread by the Early Bajocian, very early in its
evolutionary history.