TAPHONOMIC IMPLICATION OF ONTOGENETIC DISTRIBUTIONS FOR FIELDMICE (PEROMYSCUS SPP.) POPULATIONS FROM TWO DEBRIS CONE DEPOSITS, PARKER’S PIT, BLACK HILLS, SOUTH DAKOTA, USA

ABSTRACT:

Fossils accumulate in caves in multiple ways. Each introduces biases that must be understood before interpreting the assemblage. The ontogenetic age distributions of individual specimens of field mice, Peromyscus spp., based on tooth wear, provides insight into taphonomic pathways for two different talus deposits in Parker’s Pit, Black Hills, South Da- kota. Main Cone accumulated under the modern 12 m vertical pit entrance throughout the Pleistocene and Holocene. The sink hole prohibits escape of randomly selected taxa. Red Cone formed as a talus slope in an old, now closed, entrance with a ramp-like slope that allowed animals to enter and exit the cave. Differences in ontogenetic age distributions between these two populations are statistically significant. Main Cone indi- viduals show a wider and generally older age distribution than those from Red Cone. The older age distribution results from individuals surviving the vertical fall and living into old age in an essentially predator-free environment. These in- dividuals probably subsisted on organic debris washed into the cave and resident invertebrates as observed in a living population of Peromyscus pectorralis in Longhorn Cavern, central Texas. The Red Cone population is ontogenetically younger, as exhibited by less dental wear, than the Main Cone population but slightly older than living populations stud- ied in Washington, USA, and British Columbia, Canada. Bone damage indicative of predation by small carnivores, especially weasels (e.g., Mustela frenata) in the Red Cone sample is not apparent in the Main Cone population, reinforcing different taphonomic pathways of the two populations. The Red Cone sample is biased by predator selection. The Main Cone fossil assemblage likely represents a random, local sample of the biota around the cave that facilitates paleoecological analyses. The predator biased Red Cone sample is not amenable to reconstruction of communities but does provide insights into predator-prey interactions and selected species in the vicinity of the cave.