Date of Award

2019

Degree Name

Biological Sciences

College

College of Science

Type of Degree

M.S.

Document Type

Thesis

First Advisor

Dr. F. Robin O’Keefe, Committee Chairperson

Second Advisor

Dr. Suzanne Strait

Third Advisor

Dr. Anne Axel

Abstract

Elasmosauridae is a monophyletic group of plesiosaurs that evolved in the Early Cretaceous and radiated to achieve a cosmopolitan distribution by the end of the Cretaceous. They were a highly successful group of deep sea predators with long necks, small heads, and stout four flippered bodies. Here we describe four postcranial elasmosaurs skeletons that were collected from the shallow marine Lopez de Bertodano formation located on Seymour Island of the Antarctic Peninsula. One specimen is a small-bodied elasmosaurs. Despite its small size it has several advanced ontogenetic character states including the fusion of neural spines to the vertebral centra. The individual was considered to be sub-adult in age. Histological samples were taken of the right femur that showed a moderate amount of remodeling while still preserving much of the fiber lamellar bone associated with fast growing juveniles. Together these features confirm a late juvenile to sub-adult ontogenetic stage for the specimen. Two of the other specimens are moderate sized elasmosaurs with unusual characteristics sometimes attributed to the clade Aristonectinae. We use their characters along with other WBP (Weddelian Biogeographic Provinance) and Pacific elasmosaurs taxa to better understand the relationships among basal Aristonectine elasmosaurs and evaluate characters attributed to them. The final specimen is the post cranial material from the holotype for Mortuneria seymourensis. Using this taxa we can better understand potential apomorphic characters and its relationship to closely related aristonectines. This paper aims to better understand these unusual elasmosaurs and the relationships of WBP elasmosaurs.

Subject(s)

Plesiosauria.

Geology, Stratigraphic -- Jurassic.

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