THE IDENTIFICATION OF A PLIOCENE (LOWER BLANCAN), MULTI-TAXIC BONEBED IN THE PANACA FORMATION OF LINCOLN COUNTY, SOUTHEAST NEVADA

The Panaca Formation of southeast Nevada was assigned to the Tertiary by early studies based upon recovered faunal assemblages. More recent studies identified the Hemphilian-Blancan boundary in the base of the unit. Multiple studies have focused on one locality which has produced numerous vertebrate remains, including at least three mammal holotypes. As part of a paleontological resource survey supported by the Bureau of Land Management, our team was able to identify over fifty vertebrate fossil sites in the exposures of the Panaca Fm throughout Meadow Valley, NV. Upon closer inspection of the above mentioned highly fossiliferous site, known in previous studies as Rodent Ravine/Limestone Corner, we identified a multi-taxic bonebed.

The host sediment is light-brown, poorly indurated and sorted, fine to coarse sandstone. Due to modern weathering and pedogenic processes, sedimentary structures are not preserved. We note a density mediated bias in large-bodied vertebrate elements, as the most common specimens are dense manual and pedal elements. No articulated bones have been found, however we did recover a closely associated camelid metapodial and phalanges; a previous study found an associated caprine bovid, which most likely came from this same horizon. Most bones are isolated with pre-fossilization breakage. This implies this is a time-averaged assemblage, concentrated via sedimentological processes, rather than a catastrophic or biologically mediated assemblage. We also recovered microvertebrate remains, which also show preferred preservation of dense elements, phalanges, teeth, and pelvic elements. Previous studies interpret the Panaca Formation to represent a closed basin related to Neogene Basin and Range extension, developing a marshy to pluvial lake with surrounding terrestrial depositional environments. The sandy, poorly sorted matrix, with greenish poorly drained facies in close stratigraphic contact supports a hypothesis that this bonebed represents a small-scale shoreline lag deposit.

Bonebed taxa recovered from this study include a large camelid, a large carnivore, caprine, rodents, rabbits, birds and potential lizards. Taxa attributed to coming from this horizon from previous studies include a caprine bovid, as well as numerous rodents, rabbits, and other microvertebrates.