Friday I was able to spend the entire day working on the Rappahannock sperm whale (fortunate, since my poster at next month’s SVP meeting is about this specimen). I concentrated on the bone labeled as “unidentified bone” in the photo below:
The bone turned out to be the squamosal (essentially, the cheekbone). The squamosal includes the articulation for the lower jaw (the glenoid fossa), as well as a part that points forward (the zygomatic process) that attaches to the jugal, the bone that forms the bottom of the eye socket, as shown below (lateral view):
Back when I first recognized the jugal, I suspected that this whale would have an unusually long zygomatic process, and that turned out to be correct. Compare the bones above to the same bones in a modern sperm whale (the squamosal is outlined in blue, while the jugal is outlined in red):
The only named sperm whale with such a long zygomatic process is Zygophyseter, from the Late Miocene of Italy. Zygophyseter is also similar in size to the Rappahannock whale, and has the same tooth morphology. However, while the zygomatic process is very long in both specimens, it is more slender in Zygophyseter. The Italian specimen is also about 3 million years younger than the Rappahannock specimen. Hopefully things will be cleared up a bit as we prepare more of the specimen.