292-11 Revisiting the Biostratigraphy of Aplodontiid Rodents in the Late Oligocene of Western North America

Session: Life and Environments Through Time and Space: Multi-Record Approaches to Stratigraphic Paleobiology, Part II

Presenting Author:

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Abstract:

The rodent family Aplodontiidae is known today only from the Northwestern U.S. and Northern California; however, in the past, this clade had a Holarctic distribution with a center of diversity in the western U.S. through the last 30 million years. Diversity is particularly high in the late Oligocene, when rapid evolution in the subfamilies Allomyinae and Meniscomyinae as well as among some of the more derived prosciurines made this clade an excellent biostratigraphic marker taxon. The biostratigraphy in the John Day Formation published in the 1980’s is based primarily on species of aplodontiids and of geomyids (gophers) that occur through the section; unfortunately, the taxonomic descriptions of some of the species lacked the detail needed to make taxonomic designations for new specimens, and it was unclear whether the published biostratigraphic distributions of the taxa were accurate. A taxonomic reexamination of the aplodontiid rodents in the John Day and Cabbage Patch Formations reveals greater stratigraphic ranges for several of the taxa than previously reported, as well as some faunal affinities between the Northwest and the Rocky Mountains that have been suggested in past work on other rodent groups. Developing a robust taxonomy for these biostratigraphically important species allows us to look in more detail at the complex interrelationship between stratigraphy, paleoecology, and biogeography, where we find that the ecological diversity within these taxa plays a role in dictating their occurrences and renders them a bit more difficult to use in biostratigraphic work. However, the Oligocene of western North America does see significant morphological evolution within both allomyine and meniscomyine rodents that can reveal biostratigraphic affinities between localities. Further study of the ecological characteristics of these species and the paleoecosystems in which they occur will be valuable in clarifying the interaction between ecological heterogeneity and morphological change through time in dictating occurrence patterns of rodent species.

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

doi: 10.1130/abs/2025AM-10736

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