Anderson, Jason S.Campbell, James Alexander2019-12-202019-12-202019-12-19Campbell, J. A. (2019). Osteology and Histology of Plesiosaurs (Reptilia: Sauropterygia) from Non-marine (Fluvial to Estuarine) and Marine Depositional Environments (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.http://hdl.handle.net/1880/111368Plesiosaurs are a highly diverse group of secondarily-aquatic reptiles that lived from Late Triassic to Late Cretaceous time. Plesiosaurs are known primarily from marine deposits, but also occur sparingly in non-marine units. Here, I describe the osteology and histology of plesiosaurs from both non-marine (Dinosaur Park Formation, DPF) and marine (Bearpaw and Pierre Shale Formations; BF, PSF), Upper Cretaceous-aged deposits of western Canada. These sediments were deposited in the Western Interior Basin, which was inundated by a large marine corridor known as the Western Interior Seaway. Non-marine (fluvial to estuarine) sediments of the DPF have yielded a stratigraphically extensive collection of elasmosaurid plesiosaur specimens. These specimens are notable as they belong to individuals that are small-bodied relative to some elasmosaurid specimens from marine units. In this study, I test whether the small-bodiedness of DPF specimens is due to the presence of immature individuals or a small-bodied taxon. Analyses of select DPF elasmosaurid specimens indicate the presence of a small-bodied taxon. Furthermore, a well-preserved partial skeleton from this unit is recognized as the holotype of a new genus and species. The holotype and referred specimens span both estuarine and fluvial sediments and may indicate an example of niche-partitioning within the predominantly marine Plesiosauria. The small body size is also consistent with those of plesiosaurs from other non-marine units. I also describe select elasmosaurid and polycotylid specimens from the BF and PSF, respectively. One elasmosaurid belongs to a large-bodied taxon which may be closely-related to, or possibly conspecific with, the DPF taxon. Another elasmosaurid belongs to a small-bodied, likely new, taxon. The two polycotylids were originally considered to be a juvenile and adult of Dolichorhynchops bonneri, based on their similar morphologies and large discrepancy in size. However, both specimens are osteologically mature, possibly reflecting interspecific differences; alternatively, these body size differences may be due to sexual dimorphism. Finally, this dissertation constitutes one of the first histological studies on plesiosaurs from non-marine units and Canada. This study also contributes to our limited understanding of plesiosaur ontogeny.engUniversity of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.PlesiosaurElasmosauridaePolycotylidaeHistologyDinosaur Park FormationBearpaw FormationPierre Shale FormationSnakebite MemberPembina Membernon-marinemarineWestern Interior Seawayniche-partitioningPaleontologydoctoral thesis10.11575/PRISM/37360