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Mosasaurus specimen from Canada exquisitely preserved

Ben Creisler

A paper in the JVP:

Takuya Konishi, Michael G. Newbrey & Michael W. Caldwell (2014)
A small, exquisitely preserved specimen of Mosasaurus missouriensis
(Squamata, Mosasauridae) from the upper Campanian of the Bearpaw
Formation, western Canada, and the first stomach contents for the
Journal of Vertebrate Paleontology 34(4):  802-819

A new, exquisitely preserved specimen of a small mosasaur, referable
to Mosasaurus missouriensis, is reported from the Bearpaw Formation
(ca. 75 Ma, upper Campanian) of southern Alberta, Canada. Many
calcified cartilaginous elements, including tracheal rings and the
sternum, are preserved. The sternum most closely resembles that of
Clidastes propython, bearing five shallow sternal rib facets on each
side. Our comparative study of the new material with the holotype,
referred material, and the genotype M. hoffmannii is congruent with
the preexisting hypothesis that M. missouriensis and M. hoffmannii are
phylogenetically more closely related to each other than to the other
congeners, in spite of a temporal gap of nearly 10 million years
between them. Also preserved with the mosasaur, inside its ribcage and
around the specimen, are well-preserved aulopiform fish bones,
including a skull. The fish skull is punctured and its centra
truncated, suggesting macrophagy was employed by M. missouriensis
despite the apparent lack of tooth wear. A sympatric specimen of
Prognathodon overtoni is known to have consumed a sea turtle as well
as fishes, and consistently exhibits apical wear across marginal
teeth. We hypothesize that coexistence of these apex predators in the
Bearpaw Sea was possible because of niche partitioning. Finally, the
mosasaur carcass was likely scavenged by at least three lamniform
sharks, based on their shed teeth and a series of truncated transverse
processes on the mosasaur tail.