As part of a (woefully overdue) book chapter, I’ve been photographing lots of baleen whales from the Chesapeake Group, the unit which includes the Oligocene, Miocene, and Pliocene formations on the coastal plains of Virginia, Maryland, and Delaware. The vast majority of the Chesapeake Group whales have been found in the Calvert Formation, with only a few specimens from the other units. The Eastover Formation, which ranges from approximately 7-9 million years old, has produced enough scrappy remains to demonstrate that there were several baleen whale taxa present at that time, but not enough for definitive identifications. Even so, there are some intriguing remains from the Eastover.One of the most impressive is shown above. This specimen was collected from a quarry in King William County about 10 years ago (the quarry produces cat litter, so we call this the “kitty litter whale”). It was unfortunately not discovered until after quarry machinery had destroyed much of the skeleton, but we still recovered fragments of the cranium, dentary, forelimb, about a dozen vertebrae and some rib fragments. The largest cranium fragment is shown above in posterior view, and includes the left exoccipital and part of the supraoccipital. For comparison, below is a posterior view of a modern gray whale (Eschrichtius robustus, from the San Diego Museum of Natural History); the non-shaded portion is what’s preserved in the kitty litter whale:
The remarkable thing about the kitty litter whale is the size. The fragment is about 70 cm wide, so the complete skull had a posterior width of approximately 140 cm. Making a lot of assumptions about the proportions of this whale, that translates to a skull length of around 2.7 m, and a body length of around 13.5 m.
Here’s the posterior end of the right dentary, in medial view:
For comparison, here’s the same fragment next to the largest dentary we’ve found at Carmel Church:
Here’s the same image, with the comparable portion of the Carmel Church specimen indicated:
I don’t know for sure what taxon the Carmel Church dentary belongs to, but I think it’s Eobalaenoptera; it’s the correct size, and comes from a locality that is known to produce Eobalaenoptera. Eobalaenoptera is the largest whale known from the Calvert Formation, and it’s only around 8.5-8.8 m long.
Based on the remains we have, the kitty litter whale appears to be a balaenopteroid, and is probably a balaenopterid (the family that includes most modern baleen whales, including blues, fins, and humpbacks). If my length estimate of over 13 m is correct, this whale was larger than the modern minke whale (B. acutorostrata), and in the same ballpark as humpback whales (Megaptera novaeangliae).
So even though the remains are scrappy, it’s clear that by the Late Miocene we had whales in the North Atlantic that were comparable in size to some of the modern whales, which is quite a contrast with the mostly small whales in the Calvert Formation. Moreover, just based on what I could see in the field, it looks like the Yorktown whale we collected last month (also from the Eastover) is even bigger than the kitty litter whale.