Last week we discussed systematic organization of geologic collections, or organization via a Linnaean framework. This week, we’ll focus on what is probably the most favored organization scheme for vertebrate fossil collections, temporal or biostratigraphic.
Biostratigraphy, of course, is the practice of dividing sediments into discrete packages based on their contained fossils. It’s a method by which we can observe floral and faunal change throughout the sedimentary record, and interpret change over time. Collections organized biostratigraphically are, quite simply, arranged by time, oldest (or stratigraphically lowest) first, followed by younger (or stratigraphically higher). This is an extremely intuitive method that has worked well for most collections accumulated and curated since the latter half of the 20th century. Many large vertebrate fossil collections, particularly mammals, are organized in this fashion, including the University of California Museum of Paleontology, the Los Angeles County Museum, and the University of Nebraska, Lincoln. Here at the Museum of Geology, our vertebrate paleontology collections are organized in this way.
Biostratigraphic collections are often organized via a “tiered” system. The overall organizational scheme is temporal. Within this scheme, material is generally organized by locality of origin (e.g. local fauna, geologic formation), and within locality by taxon. This system emphasizes its primary benefit, preservation of contextual data. Large and diverse collections from narrow stratigraphic levels are not dispersed, but retained, thereby preserving the association of specimens and taxa as they appeared in situ. Studies focusing on faunal diversity or palaeoecology are much more easily accomplished in biostratigraphic collections.
Additional benefits to a biostratigraphic organization include its intuitive and more stable nature. While ongoing changes to the geologic time scale do occur, the overall ordering has remained stable for well over a century. It’s also a lot easier to explain the passage of time to a freshman work study or a new volunteer than it is to elucidate the intricacies of differing phylogenetic interpretations. As such, biostratigraphic organization is appealing to a broader work force.
At the Museum of Geology, we’ve discovered an additional benefit to biostratigraphic organization; it is often accompanied by convenient separation of collections, most notably by federal agency. Because federal agencies are tasked with management of very specific resources, their fossil material is often restricted to specific geologic time periods. For example, most of our Cretaceous marine material was collected on US Army Corps of Engineers lands. Our Cretaceous terrestrial material is primarily from the US Forest Service. The bulk of our Oligocene White River holdings were acquired from Badlands National Park, and our early Miocene material is primarily derived from Ogallala Lakota tribal land. Finally, our Pleistocene material from central Oregon is the purview of the Bureau of Land Management. Biostratigraphic organization simultaneously divides our collections by federal agency, thus maximizing our effective repository efforts.
Biostratigraphic organization does have its down sides. As mentioned above, taxonomic groups are split up. Anyone conducting phylogenetic studies will have to do a bit of legwork to gather the necessary specimens. Additionally, the emphasis on correct identification may be less with biostratigraphic collections. If organization is not dependent on accurate identification, then there is less need to spend additional time with precise diagnosis of specimens. The upshot to this, however, is that misidentified specimens are less commonly “lost” in biostratigraphic collections. If an important fossil is misidentified, most commonly as a fish or turtle, then that specimen may be forever misplaced within the “fish” section of a systematic collection. The appropriate squamate or bird expert may never see it, as they are not likely to spend time in other parts of the collection. However, in a biostratigraphic collection, experts will be exposed to everything from a given site, and misidentified specimens are more likely to be recognized and reported.
Finally, biostratigraphic collections require a familiarity, and comfort, with local, regional, and often, continental geology. Most collections of this type I’ve visited arrange specimens, at some level, by formation. A working knowledge of the geology of your chosen time period (which any competent paleontologist should have) is imperative to orienting yourself in these collections. If your educational background does not include a geological emphasis, these collections can be challenging to navigate.
Most geologically-oriented paleontologists prefer biostratigraphic organization. What’s your take?
Next post, which will appear after the holidays, will discuss an additional organizational scheme. Until then, enjoy your break and, good luck on finals, or get those grades in!