Using taphonomic pathways identified from modern bone assemblages to interpret vertebrate fossil assemblages

Data regarding the formation of modern bone assemblages can be of great use in interpreting patterns of bone occurrence and distribution in fossil assemblages. During February 2004, a herd of 38 cows were drowned after falling through ice on the Yellowstone River in Montana. The carcasses were interred until early April after which they were transported downstream by the spring melt waters. On five occasions between May 2004 and September 2006, the 20km stretch of river where the carcasses were deposited was revisited. The location, bone abundances, taphonomic and sedimentological characteristics of each of the carcasses that could be relocated were recorded, providing an approximately 1000-day time-series describing the taphonomic modification of the recorded carcasses.

Twelve carcasses were relocated sufficiently frequently to be statistically analysed. Assuming no a priori knowledge of the geomorphology and sedimentology of each of the carcass localities, NMDS ordinations were carried out comparing the bone abundance data from each visit to each carcass with the aim to determine whether patterns of bone abundance change were indicative of particular sedimentary environments or other taphonomic factors. Three distinct taphonomic pathways were differentiated by Q-mode analysis based on channel proximity and nature of the confining sediment.

The results of this study are of particular interest from a palaeontological standpoint as they imply that bone abundances in single source bone assemblages from large taxa in fluvial systems have a distinct, measurable taphonomic signature relating to their taphonomic pathway. Comparison with fossil assemblages from similar palaeoenvironments reveals the degree to which these modern taphonomic pathways can be identified in the geological record and hence how readily these modern analyses can be generalised through deep time.