Systematics of Plioplatecarpinae (Squamata: Mosasauridae)

• Author / Creator

  Konishi, Takuya

• The name, mosasaurs, generally refers to a group of extinct, highly aquatically adapted and large-bodied squamates that lived exclusively during the Late Cretaceous, approximately from 93 to 65 million years ago, in the oceans worldwide. Plioplatecarpines (Plioplatecarpinae) were medium-sized mosasaurs seldom reaching 10 m in total body length, generally exhibiting along their gracile jaws the lowest number of marginal teeth among mosasaurs. Remains of plioplatecarpines are abundantly found particularly from the Western Interior Basin of North America; however, their taxonomy, interrelationships, and biodiversity remained largely unexplored. A large-scale systematic review of this group of mosasaurs was conducted based on examination of nearly 500 specimens of plioplatecarpine mosasaurs collected predominantly from North America and Western Europe. From a synthesis of morphological, biostratigraphic, and biogeographic data, two new genera are erected thus recognizing as valid, 7 genera and 11 species. According to the preferred hypothesis of their interrelationships, Ectenosaurus clidastoides is found to be the basal-most member, in part as a result of its high tooth count and unusually elongate jaw morphology. The interrelationships of the remaining plioplatecarpines are resolved as follows: (Angolasaurus bocagei, ((Selmasaurus russelli, S. johnsoni), (Plesioplatecarpus planifrons, (Platecarpus tympaniticus, ((Latoplatecarpus willistoni, L. nichollsae), (Plioplatecarpus primaevus, (Plio. houzeaui, Plio. marshi))))))). The new genera, Plesioplatecarpus and Latoplatecarpus, assist in resolving the long-standing problem of paraphyly/polyphyly of the genus Platecarpus, now only recognized from P. tympaniticus, the generic type. Such establishment of new genera also reduces the average number of species per genus to a little over 1.5, but this ratio likely will increase as the number of specimens in each genus increases with future discoveries, which will then allow us to better understand intra- and interspecific variations within respective genera. In addition to the new phylogeny, a novel cranial anatomy is identified in these mosasaurs. Namely, the quadrate tilted forward in many plioplatecarpines, rather than being upright, since it was along the distal portion of the elongate suprastapedial process that the quadrate articulated with the suspensorium.

• Subjects / Keywords

  • Mosasauridae
  • Paleontology--Cretaceous

• Graduation date

  Fall 2009

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3QQ44

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.