COPROLITES FROM PIPESTONE SPRINGS MAIN POCKET, MONTANA, AND THEIR PALEOECOLOGICAL AND TAPHONOMIC SIGNIFICANCE

Pipestone Springs Main Pocket (Renova Formation, Jefferson County, Montana) has an unusually rich concentration of well-preserved small-bodied Chadronian mammals and an abundance of coprolites. Diameters of measurable coprolites varied from 4 mm to 29 mm. When plotted on a histogram, there is a very robust small diameter grouping of 269 specimens with a peak at 10-11 mm and range of 7-14 mm, as well as, a broad diameter grouping of 47 specimens without a distinct peak that has a range of 15-29 mm. Dental elements representing Carnivora are relatively rare at Pipestone Springs and of 45 specimens identified to taxon, the small canid Hesperocyon constituted 44% and the larger amphicyonid Brachyrhynchocyon 24% of the sample. If the percentage of dental remains per carnivore taxon reflects its activity at the depositional site, the smaller coprolites probably represent trace fossils of Hesperocyon. The diameter range of the larger coprolites appears to be too great to represent a single species, so they probably represent at least two larger carnivores, one likely to have been Brachyrhynchocyon. Bone is visible on the surface or cross section of 85% of the coprolites in both the large and small diameter size groups, with bone per coprolite much more abundant in the small diameter group. Although the great majority of bone is fragmentary and unidentifiable, in some cases, osteoderms, bone ends, isolated teeth, or partial dentaries/maxillae could be identified to taxon. This indicated that marsupials, lizards, lagomorphs, and squirrel-sized rodents were prey of Pipestone Springs carnivores. Based on dental elements identified from the site, where Paleolagus and Ischyromys constitute 25% and 21% of the sample respectively, most elements identified as lagomorph and rodent probably represent these taxa. Thus, Pipestone Springs coprolites provide important insight into how many and which carnivores were active in the depositional area and what taxa they were ingesting. Also, a partial maxilla with M2-4 of a small marsupial was found within a prepared Pipestone Springs coprolite. This example suggests that undigested bone from disaggregated carnivore feces was a major source of the multitude of small well-preserved dentigerous elements found at Pipestone Springs.