189-15 Did Pinnipeds With Different Modes of Locomotion Inhabit Different Paleoenvironments?

Session: Paleontology, Paleoecology/Taphonomy (Posters)

Presenting Author:

Authors:

Abstract:

Pinnipeds are one of the few vertebrate groups to return to the ocean and offer a unique perspective on the evolution of a secondarily marine lifestyle. Current research on early pinnipedimorphs has mainly focused on phylogeny, biogeographic distributions, and evolutionary pathways, but reconstructing paleoenvironments may aid in understanding the locomotion and paleoecology of these taxa. Numerous pinnipedimorph fossils from the Yaquina (late Oligocene), Nye (early Miocene), and Astoria (early/middle Miocene) Formations have been recovered from the central Oregon coast. A wide variety of locomotor modes has been suggested for the genera found in these formations (Desmatophoca, Enaliarctos, Eodesmus, Pacificotaria, Pinnarctidion, Proneotherium, and Pteronarctos), ranging from fully forelimb-dominated to fully hindlimb-dominated swimming, with the locomotion of several taxa remaining unknown or under debate. We hypothesized that pinnipedimorphs with hindlimb dominated swimming modes inhabited deeper environments characterized by smaller grain sizes, while forelimb dominated swimmers would be more frequently preserved in shallower environments. A literature review of Oligo-Miocene pinnipeds from the central Oregon coast lends some support to this hypothesis. Pinnarctidion, likely a hindlimb-dominated swimmer, has been uncovered only from mudstone localities, while Proneotherium, which has been reconstructed as a forelimb-dominated swimmer, is known only from sandstone units. In at least some cases, though, there seems to be little correlation between locomotion and preservational environment, as three genera (Desmatophoca, Enaliarctos, and Pteronarctos) have been found in units ranging from shallow marine sandstones to offshore mudstones. Future fieldwork aimed at relocating previous pinnipedimorph localities and placing them within a sedimentological and stratigraphic framework will allow a more complete assessment of Oligo-Miocene pinnipedimorph paleoenvironments. Alongside taphonomic analyses, we hope that this environmental context will inform ongoing debates and uncertainties regarding the evolution of locomotion in pinnipeds.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11243

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