Tuesday, April 6, 2010

Prep update: Purisima Formation mysticete skull 2

Hey folks,

As I mentioned in a previous post, I've been preparing a fossil mysticete skull I collected from the Purisima Formation in 2005 for a long time (i.e. 4.5 years). This winter and spring I really stepped up preparation, and you can see in these photos what the specimen looked like in January. At this point, Tom Demere of the San Diego Natural History Museum, who specializes in fossil mysticetes, tentatively identified this specimen as belonging to "Balaenoptera" cortesii var. portisi, a medium sized balaenopterid from the Pliocene of Italy, Florida, and California (Demere et al. 2005). An undescribed cranium (UCMP) from the San Diego Formation and several crania I've seen in the Purisima Formation have this same morphology, but I did not realize this taxon was B. cortesii var. portisi, or that this specimen belonged in that taxon. "Balaenoptera" cortesii var. portisi is characterized by elongate, widely diverging zygomatic processes, which these other fossils have; it appears that the zygomatics of this specimen are damaged. It is also a taxon that needs a new genus, as it definitely has features that place it outside of Balaenoptera. Tom Demere and Michelangelo Bisconti are currently revising this taxon (Demere et al., 2005).

The new Purisima mysticete skull in posterolateral view.

The new Purisima mysticete skull in anterolateral view.

The new Purisima mysticete skull in dorsal view. note the wide, triangular supraoccipital shield, a typical feature of balaenopterids.
The new Purisima mysticete skull in anterodorsal view.

Anyway, quite a bit of matrix was left at this point. Soon, I'll post pictures of the specimen after preparation is completed.

Deméré, T.A., A. Berta, and M.R. McGowen. 2005.
The taxonomic and evolutionary history of fossil and modern balaenopteroid mysticetes. Journal of Mammalian Evolution 12:99-143.


J. Velez-Juarbe said...

Thats some nice prep work and nice skull too!! Has it been all mechanical or have you tried acetic acid?
So is this new skull definitely that of "Balaenoptera" cortesii var. portisi?

Doug said...

Cool post. After looking at all the score marks, i take it the matrix is pretty tough?

Robert Boessenecker said...

Hey Jorge and Doug,

This has all been mechanical. Due to the large size and extreme weight, I chose not to do any acid prep (I also started this long before I began using acid). And yes, the matrix is extremely tough; harder than anything else I've ever prepared. Unfortunately, there was no contrast in hardness between the rock and bone, so bone flaked off in many places, and in the temporal fossae, there are elongate score marks; the rock took quite a bit of bone with it.

I think Tom's probably right about the ID; the skull is incomplete, but it does have several of the features of that taxon.