Friday, April 27, 2012

Research Update: Hydrodynamic Properties of Pachycephalosaurid Crania

On Monday of this past week I had the pleasure of seeing my first research student at UW Oshkosh, Carol Bigalke, give her first talk at professional meeting. At the North Central GSA in Dayton, Ohio, Carol presented on "Hydrodynamic properties of pachycephalosaurid crania". Carol has been working with me on pachycephalosaurid cranial lesions since I started at UWO in the fall of 2010, and will be graduating this summer.

Resin cast of Stegoceras validum.
When she submitted her abstract to GSA in January, it was intended to be a poster. However, due to a need to fill the oral session, the session chair contacted her, praised her abstract, and invited her to give a talk instead. I can say with all honesty that she nailed it on Monday. She handled questions very well and fostered further discussion later in the day with other curious participants. Congratulations, Carol!

 The hydrodynamic processes of isolated dinosaur bones in general have been overlooked in scientific research. Pitting and erosive structures on pachycephalosaurid frontoparietal domes have been attributed to taphonomic processes, such as weathering and erosion. Furthermore, the high frequency of isolated domes characterizing the pachycephalosaurid fossil record suggests a unique taphonomic history. In order to investigate the hydrodynamic properties and potential roles of taphonomic processes on pachycephalosaurid domes, a series of transport experiments were conducted to assess the competent velocities and settling orientations of a collection of pachycephalosaurid specimens. 
Resin casts of Hansseusia sternbergi used
in flume experiments.

Casts of three pachycephalosaurid domes and skulls were composed of a urethane resin with a comparable average density to compact and cancellous bone (r = 1500 kg/m3), and placed in a flume with manual velocity control for transport experiments. 

Data was recorded for competent velocity, transport distance, and settling orientations upon resting and burial of specimens for 35 trials per cast. Though specimens vary considerably in mass, the results suggest specimen shape has a greater influence on transport and hydrodynamic behavior than size; significantly lower velocities are required to transport complete skulls than isolated domes. 

10-meter flume
UW-Milwaukee Department of Geology
Resting and burial orientations of specimens vary significantly for domes and skulls. Isolated domes generally settle and rest on a dorsal or ventral side with their lateral sides facing upstream. Alternatively, complete skulls have a higher tendency to rest on a lateral side compared to isolated domes. These results suggest domes are likely deposited as lag following disarticulation from other cranial and skeletal elements. The near-equal occurrences of domes resting on dorsal and ventral sides is at odds with the exclusively dorsal distribution of pitting and “erosive” features on frontoparietal domes, suggesting taphonomic processes are not a primary cause of these features. The high variability of transport velocities and settling orientations such as these offer significant implications for future taphonomic studies on large vertebrate remains.

(All molding and casting was performed with permission from lending institutions - Thanks to Scott Williams at the Burpee Museum of Natural History and Don Brinkman at the Tyrrell Museum of Palaeontology. Very special thanks to the Dinosaur Research Institute which supported this research!)