ISOLATING ABIOTIC FACTORS IN VERTEBRATE BONE TAPHONOMY: A PILOT STUDY

Previous studies of vertebrate taphonomy have focused on skeletons and carcasses laid out in a natural environment, subject to all the biotic and abiotic factors that might come into play over the years. We conducted a pilot study isolating a handful of abiotic factors in a lab setting. Large metacarpals were isolated from butchered white-tailed deer (Odocoileus virginianus). Three to four metacarpals were grouped together for each experimental treatment: control, temperature cycling, freeze-thaw cycling, wet-dry cycling, and UV cycling. The breakdown of the bones was monitored biweekly, using a modified Behrensmeyer scale. The formation of both surface and penetrative cracks were found to follow a common patterns across treatments. Surface or shallow cracks would appear as clusters of very small (a few mm in length) cracks roughly parallel to the long axis of the bone. Over time, these small cracks would grow and connect, forming long cracks (cms in length). Shallow cracks tended to concentrate on the lateral and posterior sides of the metacarpals. Shallow cracking was most extensive in the freeze-thaw treatment. Deep cracks, whether open or closed, would also form roughly parallel to the long axis of the bones, although in far fewer numbers than the shallow cracks. These would often first appear cms in length, often extending over time until they reached both ends of the bone. Deep cracks would also form or grow at oblique angles, connecting parallel deep cracks with each other, forming the beginning of chipping. Deep cracks were most seen on the lateral and anterior sides of the metacarpals. Deep cracking and chipping was most advanced in the temperature cycling treatment. Open deep cracks formed early in the wet-dry treatment. Bleaching was most extensive in the UV treatment, which showed few cracks and no chipping. Temperature changes associated with seasonal fluctuations might be the most damaging abiotic factors in isolation. This matches some of the data from a study of carcasses in a natural setting, where a lot of taphonomic changes are observed during the spring.