I’m still sorting through Ron Ison’s donation of fossils collected from the bottom of several coastal plain rivers in Virginia. One bag of specimens was mostly whale tympanic bullae (one of the ear bones). While the age of these specimen is uncertain, given the location where they were collected they are most likely from the Early Pliocene Sunken Meadow Member of the Yorktown Formation, although the Late Miocene Eastover Formation is a possibility.
Almost all the tympanic bullae in the collection are from the Balaenopteridae, the family that includes modern rorquals such as the blue and humpback whales. The two specimens at the top are both examples of balaenopterids, but I’m not sure what genus they represent (all the images are in ventral view, more or less).
One specimen was an extremely weathered example of Balaena, a right whale, easily recognized because they are so dramatically flattened:
Two of the tympanic bullae were more difficult to interpret, however. I believe the one below may be a balaenopterid, but if so it would seem to represent a different taxon than the one shown at the top of the page (note the scale bar in each image):
Again, it’s quite small, but even in its heavily-worn state it has a prominent sharp keel and median furrow. We actually have another bulla in the collection, collected from the Yorktown Formation in Surry County, that is somewhat similar (though not identical).
This specimen shows some similarity to bullae from Herpetocetus collected from the Yorktown Formation at the Lee Creek Mine in North Carolina, and it is also somewhat similar to Piscobalaena from Peru. Both of these taxa are included in Cetotheriidae sensu stricto, and I believe this is an example of a true cetotheriid.