SPECIALIZATION IN CONSUMPTION OF ANTLERS AND POSTCRANIA BY ARCTIC MAMMALS

Despite being avid bone consumers and generally having greater abundance than co-occurring carnivores, the taphonomic impacts of ungulates on bone completeness and survival are under-explored. Here, we reevaluate and further develop the criteria used to identify ungulate gnawing. We then assess the exploitation of bones by co-occurring ungulates, carnivores, and rodents to evaluate resource competition among bone modifiers and consumers. We focus on bones accumulating on modern caribou calving grounds of the Arctic National Wildlife Refuge (Alaska), where adult female caribou experience elevated nutrient stresses due to calving and antler regrowth. Exhaustive sampling of standardized taphonomic surveys yielded over 1,000 antlers and several hundred postcranial bones. Each element was visually inspected for modification features and compared to established criteria for identifying modification by local ungulates (Rangifer), carnivores (Ursus, Canis, Vulpes) and rodents (Urocitellus, Microtus). We identified 22 modification classes with characteristic pits, punctures, furrows, scores, and fractures, which we attributed to caribou (n=12 classes), carnivores (n=1), rodents (n=1), or to non-gnawing damage (n=8). Among classes of ungulate modification, nine were previously undocumented, including triangular-shaped punctures. These punctures are visually distinct and facilitate identification of bones with only minimal modification by caribou (~25% of gnawed antlers), which were not identifiable using previously established criteria. We find that ungulates and carnivores target different components of the bone assemblage. Caribou gnawing is recognized on nearly 90% of all shed antlers, but <10% of postcrania. Caribou gnaw antlers from the distal-most point downward, preferentially targeting outer tines. Carnivore modifications were readily observed on postcrania (>30%), but not present on shed antlers. Rodent gnawing was limited on antlers (<3%) and postcrania (<5%). Ungulates can be prolific bone modifiers and may drive bone recycling in some settings. We also note apparent specialization in consumption of either antlers or postcrania by co-occurring taxa.