After I collected the posterior part, I tried to excavate the anterior portion; I successfully removed two segments which broke along natural cracks, and a third portion (which I figured at the time was the anterior tip) which was stuck in a nodule, and was rather stubborn. I decided to leave that part in the cliff, and return later under more favorable conditions. The next few visits it remained, and I checked up on it; I figured noone else would disturb it (or even spot it). Well, I got lazy, and over thanksgiving, I returned with the intention of collecting it, and some fresh pick marks were around it, and whoever it was had chipped away a little bit of bone, much to my chagrin. Anyway, I excavated the rest of it immediately; fortuitously the other person had started a trench around the concretion, so it took a mere 5 minutes to carve around it and pop it out - and it did make a 'pop' sound and land with a resounding thud on the beach sand, to which I said to myself "if I had known it would have been that friggin easy, I woulda done it two years ago!".The anterior dentary before and after chiseling.The problem was, I had no idea whether or not the two pieces would even connect, given the damage done by the other collector, and two years of erosion. And I had to fly with the fossil in my duffel bag all the way back here to Montana to find out. I "gingerly" chipped away some pieces of the concretion with a rock hammer and chisel, which split the rock from the bone perfectly.
The anterior 1/3 of the Herpetocetus mandible.
Then, when I got back to Bozeman, I took the fossil to campus and nervously matched up the two sides - a lot of bone was definitely missing, but (thank god) the two pieces matched up along the ventral side of the bone, preserving the natural length (which is kind of moot anyway, given that I'm missing the middle - kind of, because I measured the missing distance when I was in the field). Some major acid preparation is in order, as well as some serios airscribing and microblasting on all three pieces. These specimens are very similar to mandibles of Piscobalaena, a cetotheriid from the Pliocene of Peru, and the probable sister taxon to Herpetocetus (Bouetel and Muizon, 2006). To be totally honest, the piece of the mandible I've shown you looks pretty damn similar across much of Chaomysticeti (baleen bearing mysticetes), with the possible exception of balaenids.
This is one of five partial Herpetocetus dentaries I've collected from the Purisima Formation (none are currently in museum collections at UCMP or SCMNH), and is the second most complete specimen; one is a complete, ~4' long, very large and robust dentary, and the others are all posterior dentaries (i.e. posterior 1/3). Two of these are extremely small (i.e. one is a fragment where the shaft of the dentary was only 2.5cm high), and likely represent neonates or extremely young individuals. These specimens, along with a nearly complete skull, a partial skull, half a dozen petrosals, and several tympanics will be the subject of a study by Jonathan Geisler and myself. In addition, there are two more possible (one definite) Herpetocetus crania in-situ, which will (hopefully) be excavated over winter break.
For more information on cetotheriids, see Alton Dooley's recent post on cetotheriids at Updates from the Vertebrate Paleontology Lab.
Bouetel, V., and C. de Muizon. 2006. The anatomy and relationships of Piscobalaena nana (Cetacea, Mysticeti) a Cetotheriidae s.s. from the early Pliocene of Peru. Geodiversitas 28:319-395.