New published article (Part 1): herpetocetine jaws, and an example of finding a "simple" research project

The new issue of PaleoBios, the paleontology journal published by UCMP at UC Berkeley, includes my new article on herpetocetine jaws from the Santa Margarita Sandstone in central California. During the fall of 2008, I was in my first semester of graduate school, and was taking a difficult, time-intensive course on advanced stratigraphy. At the time, I already had two articles I had been working on: one on my undergraduate research concerning a new fossil vertebrate assemblage from the Purisima Formation, and another on Plio-Pleistocene fur seals from the Wildcat Group in northern California (both are currently in press). However, neither was in any shape to be published anytime soon - one was only half written, and the one that was nearly finished needed a lot of work (i.e. quality control). I needed a new manuscript to work on, to give me something to do that semester aside from stratigraphy, which had started to eat away at my brain. In other words, I needed to start something fresh from scratch, with a clear beginning, a clear end, and a clear message.

The right dentary of UCMP 85431. Scale bar =10cm. From Boessenecker (2011).

A month earlier, I had given a presentation (coauthored with Jonathan Geisler) on a new skull of Herpetocetus bramblei I had collected from the Purisima Formation in 2007. While ruminating on possible projects, I suddenly remembered a partial lower jaw from the Santa Margarita Sandstone that looks a lot like the lower jaw of Herpetocetus*. The problem is, the Santa Margarita Sandstone is early Late Miocene in age (10-12 Ma), while the oldest known bona fide specimens of Herpetocetus are latest Miocene to earliest Pliocene in age (~5 Ma). In fact, the oldest known described specimen is the fragmentary type specimen of H. bramblei, which is right about 5.33 Ma. So, this specimen (UCMP 85429) is MUCH older than any known specimen of a "true" Herpetocetus.

*All species of Herpetocetus have relatively similar lower jaws, and currently the lower jaw has only been described for the type species, Herpetocetus scaldiensis (the type specimen of which is a lower jaw - more on this later).

The left dentary of UCMP 85429; scale bar = 10cm. From Boessenecker (2011).

The lower jaw of baleen whales has long been assumed to be a fairly diagnostic element, at least in certain groups. Herpetocetus scaldiensis certainly has a very distinctive mandible. Other fossil mysticetes certainly have distinctive mandibles as well. Many fossil mysticetes (H. scaldiensis, Balaenoptera davidsonii, Archaeschrictius ruggieroi, etc.) have been described just off of their lower jaws. Are dentaries really that diagnostic? Perhaps. Demere (1986) used mandibular features to reevaluate "Eschrichtius davidsonii" from the San Diego Formation, which was a chunk of a 30% complete mandible, missing the anterior and posterior ends. Being able to refer a new dentary to this taxon, he demonstrated that the "davidsonii" morphotype was actually a rorqual, and assignable to the genus Balaenoptera, which led to its recombination as Balaenoptera davidsonii. Clearly, mandibular morphology is important, and can be used to assess the taxonomy of certain groups, and 'fix' the taxonomy of certain problem taxa. Are these specimens the oldest known records of Herpetocetus?

Reconstructed lower jaw of Herpetocetinae genus and species indet., based on UCMP 85429 and 85431. From Boessenecker (2011).

Reflecting upon the known fossil record of "true cetotheres" - relatives of Cetotherium and Herpetocetus (an entire other topic worthy of its own post) - I was able to formulate some interesting questions I could ask (and attempt to answer), which would make a nice core of an article. With these objectives in mind, I started taking copious notes on the anatomy of the fossil specimens, and eventually typed these notes up into an anatomical description for the article. By the end of the semester, I had a manuscript that was about three-quarters finished. During spring 2009, I wrapped up the discussion, and constructed some figures. I had a few people look at it and make some comments. Morgan Churchill looked at it late in spring, and had some of the most constructive and useful edits. That summer, I TA'd the Geology Field Course for MSU, and during some of the weeks, I took my manuscript out into the field with me, along with a red pen. In between helping students, I sat out in the hot sun, and critically examined every sentence in the manuscript. I even drafted one of the figures (on vellum, with nice pens) around the campfire one night after a few beers. By the end of the second to last project at field camp, I had all my edits finished, and I sent it off to PaleoBios for review.



To be continued...

Boessenecker, R.W. 2011. Herpetocetine (Cetacea:Mysticeti) dentaries from the Upper Miocene Santa Margarita Sandstone of Central California. PaleoBios 30:1:1-12.

Deméré, T.A. 1986. The fossil whale, Balaenoptera davidsonii (Cope 1872), with a review of other Neogene species of Balaenoptera (Cetacea: Mysticeti). Marine Mammal Science 2:277–298.