Those Queer Amphibious Animals: Digging into the Fossil Record of Otarioid Pinnipeds to Investigate their Early Diversification, Locomotor Evolution, and Conservation Biogeography
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Date
2024-01-10
Authors
Tate-Jones, Kellum
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Seals, sea lions, walruses, and their extinct relatives and ancestors have played a critical role in marine ecosystems for over 25 million years. Known collectively as pinnipeds, these secondarily aquatic animals are unique among modern marine mammals for their obligatorily amphibious lifestyle and display remarkable ecological diversity, employing a range of strategies for aquatic locomotion and occupying coastal and pelagic habitats from the tropics to the poles. In addition to their extant representatives, their fossil record contains over a hundred named pinniped species, although the majority of these species are relatively derived members of the Phocidae (true seals), Otariidae (eared seals, including sea lions and fur seals), and Odobenidae (walruses). In my first chapter, I contributed to our understanding of early pinniped evolution by describing the new species Eodesmus condoni and performing a phylogenetic analysis to determine its placement within Pinnipedia. My analysis resolved E. condoni as the most basal species yet described of the extinct pinniped family Desmatophocidae. I then explored the evolution of aquatic locomotion in otarioid pinnipeds (otariids, odobenids, and desmatophocids) by using three-dimensional geometric morphometric analyses to first investigate the relationship between humerus morphology and swimming modes and then to predict the swimming mode used by fossil otarioid taxa. My results supported the plesiomorphy of hindlimb-dominated propulsion in all pinnipeds as well as the Otarioidea, with forelimb propulsion evolving three separate times: in the lineages of desmatophocid Allodesmus kernensis, odobenid Pontolis barroni, and an ancestor of modern Otariidae, likely through exaptation of humeral structures that first evolved for pinniped terrestrial locomotion. Finally, I use ecological niche modeling to compare the range of environmental conditions inhabited by the sole surviving walrus Odobenus rosmarus during the Pleistocene to the conditions in which it currently resides. This study reveals that during the Pleistocene, the regions where O. rosmarus lived encompassed warmer conditions than its current range. Contrary to predominant narrative about walrus response to climate change, these findings suggest that O. rosmarus may indeed be able to survive in the seasonally ice-free conditions that will characterize the Arctic in the coming decades. This dissertation includes previously published and unpublished coauthored material.
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Keywords
Conservation paleobiology, Functional morphology, Marine mammals, Paleontology, Pinnipeds