Friday, December 31, 2010

Research Update: Upcoming Publication on Biases in Microvertebrate Accumulations

Microsites (any localized accumulations of small vertebrate fossils) are relatively commonly occurrences in vertebrate paleontological field work, and are frequently used for paleoecological interpretations (if that can actually be done…the problem I have with term “paleoecology” I will address in upcoming posts for sure…) regardless of taphonomic provenance. On more than one occasion I have seen posters at conferences presenting the paleoecology of a site based on a handful of highly abraded microvertebrate fossils obtained from coarse-grained sandstones with high-angled cross-beds; truly staggering.
To be fair, a number of studies have been conducted on microsites and assemblages that do take taphonomic provenance into consideration and some have debated the usefulness of microsites for such interpretations with varied results (e.g. Dodson, 1973; Blob & Fiorillo, 1996; Smoke, 2004; Wilson, 2008).
Why the variation? Because there is no established protocols for microsite collecting, resulting in biased datasets and interpretations. Two methods are commonly employed for microsite collection. The first of these methods is surface collection, in which weathered specimens are picked from the surface of the rock and in talus piles. This method commonly involves the selection and collection of larger and more easily identifiable specimens. The second method is quarrying and disaggregation, which requires excavation, collection, and total screen rinsing of a large volume of rock; this method is utilized in order to recover all fossils present.
In 2005 we started a project to investigate the potential biases on taphonomic reconstructions that result from non-standardized collecting of microvertebrates in the Hell Creek Formation. The results of this study will be published in PALAIOS in the New Year (finally)!
For our study, these two commonly used collection methods were compared from two different microvertebrate localities in the Upper Cretaceous part of the Hell Creek Formation of southeastern Montana in order to identify their influence on taphonomic interpretations. Both methods were applied at two sites of significantly different lithologies; sandstone-dominated and a mudstone-dominated sites. The results of a quantitative analysis of these two common collection methods demonstrate how each one influences fossil recovery according to shape and size by skewing the characteristics of collected fossil assemblages and the taphonomic interpretations of microvertebrate accumulations. Although the study sites reflect only two possible types of microvertebrate localities, the results are applicable to many microvertebrate studies.
Earth shattering? I won’t flatter myself. This study went through many phases and the manuscript went through a LOT of revisions so I’m just happy that it is finally coming out. This was my first project that I cut my teeth on towards my dissertation; something of a baby to me…I’ve seen it come so far. However, I still feel that there is potential to further work here. I’m very interested in thoughts, comments, or suggestions.

Monday, December 13, 2010

Research Update: Pachycephalosaurids at North Central GSA

My students and I at UW-Oshkosh, as well as a few collaborators around the country, are working on a study involving abnormal structures on pachycephalosaurid crania. Our goal is to differentiate taphonomic artifacts from structures that have potential to be paleobiological in origin. We have just submitted two abstracts for North Central GSA for 2011 dealing with this current project.

From interactions I've had with other researchers in marginocephalian paleobiology or dinosaur taphonomy in general, I'm getting the impression that there is an assumption that if you are studying abnormal structures on a dinosaur skull, you are probably going to call everything a pathology. While I understand the concern based on how common it is to come across manuscripts that make such leaps, this is something we are being very careful not to do. It should be noted, however, that there are manuscripts that have labeled lesions as "pathologies" and have not done so haphazardly (e.g. Wolff et al., 2009; Peterson et al., 2009; Longrich et al., 2010).

Most abnormal structures seen on pachycephalosaur crania are casually disregarded as "water wear". However, this has yet to be tested and reported on in the literature. I have yet to see a thorough, detailed analysis of pachycephalosaur dome "lesions" in order to investigate potential etiologies. As such, that is our main goal. A similar approach was taken by Tanke and Farke (2006), in which bone resorption was identified as a primary etiology for abnormal cranial lesions on ceratopsians.

And, of course, there is the real question regarding pachycephalosaurs: frontoparietal dome function. What might these little erosive structures suggest about the function of a pachycephalosaurid dome? That is the real question.