AMIDST A SEA OF DUST AND ROCKS: RECONSTRUCTING A FAUNAL COMMUNITY AND LANDSCAPE FROM A 500,000-YEAR TIME SLICE OF THE PLIOCENE AT HAGERMAN FOSSIL BEDS NATIONAL MONUMENT

The 4,200 acres of fossiliferous bluffs at Hagerman Fossil Beds National Monument (HAFO) date to the early and late Pliocene (>4.1Ma to 3.07Ma). Its ~200m stratigraphic sequence reflects a landscape mosaic of lake and riverine environments that likely changed dramatically over its 1.5 million plus years of depositional history. Lake cyclicity would have transformed the landscape, with fluvial deposition and scouring further altering the paleotopography. Here, the Hagerman Paleontology, Environments, and Tephrochronology (PET) Project presents a landscape-scale community reconstruction for an ~500,000-year time slice. This is the first in a series of landscapes that we plan to target as we begin to unravel not only HAFO’s taxonomic diversity, but also how that diversity changed across time and space.

The PET Project recognized HAFO’s complex depositional landscape and issues with the over-simplification of treating it as a single, spatially-temporally autochthonous assemblage. Tephrostratigraphic mapping of the monument and ongoing dating of volcanic deposits provide opportunity to confidently date fossil outcrops relative to each other, providing smaller time slices on which to place our lens of inquiry. Here, we take paleontological data from sedimentary sequences between two ash layers: bed J and the Fossil Gulch ash layer. We selected this interval as it provides a refined time slice across the entire monument.

Hagerman’s Blancan-age fauna is diverse with ~200 species. Twelve mammal species, seven bird families, and a variety of diatoms occur within this specific sequence. Woodland is indicated by the presence of browsing (camel, sloth, mastodon), roosting (passerines, hawk), and climbing (grison, racoon, cat) taxa. Horse, marmot, and coyote indicate grasslands. Otter, beaver, and water birds (swan, grebe, heron, rail) well-reflect the widespread presence of lake, river, and wetlands. Diatoms point to nutrient-rich open water, lake margin, and wetland habitats. We further break down the community spatially to showcase differences in biodiversity and inferred habitat across this landscape. Diatoms allow for even further refinement, including taxa showing evidence of lake cyclicity at the Sahara site and preservation indicative of high energy water flow in the area below the Horse Quarry.