Abstract - Comparative Taphonomy of Holocene Microvertebrate Faunas Preserved in Fissure Fill Versus Shelter Cave Deposits
Benton, Rachael Carol. 1999. Comparative Taphonomy of Holocene Microvertebrate Faunas Preserved in Fissure Fill Versus Shelter Cave Deposits. PhD Disseration. University of Iowa. 261 p.
Evaluation and comparison of taphonomic mechanisms from two Holocene deposits provide insight into differences between cultural and non-cultural accumulations. Sediments and vertebrate remains from the Beaver Creek Shelter, Wind Cave National Park, Custer county, South Dakota, are the product of fluvial overbank flooding, predator accumulations, cultural influences, and from animals that resided in or around the site. The Fossil Ridge Fissure accumulations, located in southwestern Wyoming, are part of an ongoing depositional process involving predator accumulations and packrat nesting. Although clay, silt, and fine-grained sand deposited in the Beaver Creek Shelter are fluvially derived, individual osteological elements were not hydrodynamically sorted. These elements are larger than enveloping clasts, and lack rounding or abrasion. Sediments from the Fossil Ridge Fissure accumulations resulted primarily from freeze-thaw activity and consist of large blocks of weathered Green River Formation and decayed organic material. Artifacts, burned bone, and fragmented large mammal bone concentrated in Horizons 12 through 17 of the Beaver Creek Shelter provide evidence for human habitation between 3870+70 and 6720+100 years BP. Sedimentary horizons above and below this section contain very few cultural features. The Fossil Ridge Fissure deposits examined fissures were at least 6 meters from the exposed hillside and thus would be accessible to humans only through modern quarrying activity. Holocene vertebrate remains from both sites compare favorably with those in recent raptor pellets, nest debris and mammalian carnivore scat in terms of taxonomic composition, bone breakage, and corrosion patterns. The occurrence of certain taxa varied between both sites and the recent predator collections. Differences reflect seasonal changes and variations in predator and prey activity. High proportions of incisors and molars to post-cranial elements within the Fossil Ridge Fissure accumulations suggested potential snake predation. However, the low number of snake elements and the lack of snake taxa that preferred ectothermic prey, suggest that snake predation was not a significant factor. The robust nature of cranial elements within some fossorial taxa such as the gopher could lead to the preferential preservation of molars and incisors. Packrats and deer mice occur throughout the section at Beaver Creek and at Fossil Ridge Fissures and are well represented by cranial and post-cranial elements. Both of these taxa are believed to be site residents. The occurrence of amberat, seed caches, gnawed bone, and decayed feces within the Fossil Ridge Fissures further support packrat and deer mouse habitation. Because the Fossil Ridge Fissure accumulations are located further into the hillside than most raptor nests, packrats probably collected pellets, scat, and bone to sue in nests and their fortification within the fissures. Although packrat and deer mice remains occur throughout the section at the Beaver Creek Shelter, evidence for habitation by these taxa is less pronounced. Periodic flooding of Beaver Creek may have limited preservation of amberat and decayed feces.