QUANTIFYING POTENTIAL MOBILITY VERSUS ACTUAL TRANSPORT DISTANCE OF VERTEBRATE SKELETONS: EXPERIMENTAL METHODS FOR EXAMINING FLUVIAL TAPHONOMY IN THE FOSSIL RECORD

Understanding taphonomic processes that shape the fossil record is integral to interpreting the composition and function of extinct ecosystems. Bones preserved in fluvial environments make up a major part of the vertebrate fossil record, and unsteady state flows (flooding, crevasse splays, debris flows, etc) are often invoked as drivers of mobility and agents of burial, in addition to steady state river flow. Experiments have explored the fluvial transport of mammal skeletons, but other vertebrates, especially extinct clades, have only been sparingly studied. Because of this, researchers have raised concerns that non-mammalian bones could exhibit different mobility and sorting patterns in the fluvial fossil record. Here we investigate the mobility of weighted hadrosauroid dinosaur bone models and modern sheep bones in a large-scale flume setup.

In steady state conditions, mass and bone shape have important effects on the critical mobility conditions for hadrosauroid skeletal elements. Under flash flood conditions, we find that bone mass and shape are significantly correlated with travel distance by both the model hadrosaur postcrania and the sheep bones. Our hadrosauroid bone models sort into statistically significant groups based on transport distance. These groups share some overall similarities with the original Voorhies Groups, but group placements of some elements are variable based on differing morphologies from mammal bones. As a result, we used our experimental data to guide development of non-dimensional mathematical models to predict behavior of bones of various shapes in flow. This will facilitate quantitative comparisons of spatial distributions of specimens at fossil sites where hydrological parameters may be difficult to estimate. More quantitative methods will help to produce more precise interpretations of depositional environments and biostratinomy of fossil quarries and aid in clarifying bias in the fluvial fossil record.