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Russellosaurus coheni n. gen., n. sp., a 92 million-year-old mosasaur from Texas (USA), and the definition of the parafamily Russellosaurina

Published online by Cambridge University Press:  01 April 2016

M.J. Polcyn  and
G.L. Bell Jr.
M.J. Polcyn*
Affiliation:
Shuler Museum of Paleontology, Southern Methodist University, Dallas, Texas 75275, USA
G.L. Bell Jr.
Affiliation:
Guadalupe Mountains National Park, Salt Flat, Texas 79847, USA
*
* Corresponding author. Email: [email protected]

Abstract

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A new mosasaur, Russellosaurus coheni, is described from the Collignoniceras woollgari Zone (lower Middle Turonian) at Cedar Hill, Dallas County, Texas. At approximately 92 Ma, it is the oldest well-preserved mosasaur skull from North America. It possesses characters diagnostic of Plioplatecarpinae but retains numerous plesiomorphies as well. Phylogenetic analysis indicates a close relationship with Yaguarasaurus columbianus, and these two, together with Tethysaurus nopcsai, form a clade that occupies a position basal to the divergence of the subfamilies Tylosaurinae and Plioplatecarpinae. Russellosaurus coheni is proposed as the nominal taxon of a new mosasaur clade, parafamily taxon novum Russellosaurina, which includes Plioplatecarpinae, Tylosaurinae, their common ancestor and all descendants. Tethysaurus retains a plesiopedal limb and girdle morphology, and along with Russellosaurus and Yaguarasaurus, cranial plesiomorphies. Dallasaurus turneri, a temporally and geographically sympatric plesiopedal mosasaur, occupies a basal position within Mosasaurinae. This phyletic arrangement confirms that marine adaptations, such as development of paddle-like limbs, occurred independently in at least two lineages of mosasaurs, once within Mosasaurinae and once within Russellosaurina.

Keywords

MosasaurPlioplatecarpinaeTethysaurusTuronianYaguarasaurus
Type
Research Article
Information
Netherlands Journal of Geosciences , Volume 84 , Special Issue 3: Proceedings of the First Mosasaur Meeting , September 2005 , pp. 321 - 333
Copyright
Copyright © Stichting Netherlands Journal of Geosciences 2005

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