Injured fossil mysticete and an investigation of osteosclerosis (and benthic feeding?) in fossil mysticetes

I'm sorry to have been inactive for so much of the last month, but I've been busily trying to get some papers completed before the all-consuming teaching schedule takes over my life (1st year Anatomy course started today). I will try to be more active and regular with the blog, I promise.

So, to kick off a rejuvenated series, I thought I'd post something new of mine. Below is a press release by the Virginia Museum of Natural History concerning a paper just published through their in-house journal by me and Alton "Butch" Dooley (which is open access at the Jeffersoniana page at the VMNH), a good friend and colleague. After my paper with Bruce Rothschild in 2008 on decompression syndrome in cetaceans, I've had lots of people approach me about paleopathology, and though I am cautious about doing more than I am comfortable with, this project was irresistible.


VMNH assistant curator of vertebrate paleontology, Dr. Alton Dooley, burshes off dirt from the jacket protecting the unearthed whale skull in July 2006 (VMNH)


Butch had been collecting from a Calvert Formation locality (middle Miocene) known as Carmel Church, in VA. He has a very active dig going on with loads of great finds and volunteers that make it really a spectacular piece of work. One of the more complete whales he uncovered was that of an animal known as Diorocetus. It is a mid-sized "cetothere"-grade mysticete whale and this was an exceptionally well preserved specimen, with much of the skeleton and skull intact.


A dorsal view of the baleen whale's skull (Credit VMNH)


First, the whale has an unusual partially-healed break in its mandible. That alone is curious and worth a little discussion. And although I still think we need to take any interpretations of its cause and implications for behavior with a good amount of caution, to me the best part of it has been that this fossil stimulated something else - a look at osteosclerosis in mysticetes. This animal, probably Diorocetus, has some seriously osteosclerotic ribs. It is hard to find good diagnostic specimens of mysticetes that have decent skulls with associated ribs (partly because they are a pain to collect), so when we looked at this we couldn't believe it when we saw this classic "cetothere" with ribs that almost have as much cortical bone thickness as a manatee! Ok, that is perhaps a bit exaggerated, but it is significantly thicker than that found in odontocetes.


An artist's rendition of the possible feeding habit of the baleen whale (Credit Michael Morriss-VMNH)


So then we decided to look for osteosclerosis in other mysticetes, especially fossil taxa, and found that in our preliminary sample that some of the oldest mysticetes, including toothed mysticetes like Aetiocetus, they had a very advanced form of osteosclerosis, and that only "modern" mysticetes, particularly rorquals, have more porous bones like those seen in odontocetes. What this implies for the evolution of benthic feeding and filter feeding in general with mysticetes is interesting, and discussed in the paper'sm discussion section.

In the end, I think we stumbled upon an interesting sort of data about osteosclerosis that we would not have thought to seriously investigate if not for this curious injured individual from Carmel Church. As you will see in the press release, the interpretation of this individual is what gets the hype, although I am personally more confident and thrilled by the osteosclerosis bit. Still, it is food for thought and reminds us that even filter feeding with baleen is not a simple, one-style-fits-all sort of feeding, and it may have started out in a much different way than we may have previously thought.

I would urge you to read the paper and judge it for yourself. The disucssion of the cause and behavior associated with this individual specimen is meant to be speculative, although an intriguing idea, but the best part is the osteosclerosis (in my opinion). Well enough of me, read on....!

*****ALSO - for another media release about this, see the article in the Virginia Pilot, including comments by Mark Uhen and Nick Pyenson.



VMNH PRESS RELEASE


CONTACT:
Ryan Barber
(276) 634-4163


Virginia Museum of Natural History releases 20th installment of the Jeffersoniana scientific publication series
Publication features first published evidence of bottom feeding habits in extinct whales.


MARTINSVILLE, Va. (August 19, 2009) - The Virginia Museum of Natural History has released the 20th installment of its Jeffersoniana scientific publication series, which is now available as a free download from the museum's online store. The publication, titled "Injuries in a Mysticete Skeleton from the Miocene of Virginia", focuses on the mostly complete fossil skeleton of a baleen whale discovered during a museum excavation at the Carmel Church Quarry in Caroline County, Virginia in 2006. Unique features from these particular remains had never been documented in any other fossil baleen whale and give evidence to suggest several previously unpublished theories of the feeding habits of this now extinct species.
Co-authors Dr. Brian Beatty, VMNH museum research associate and assistant professor of anatomy at the New York College of Osteopathic Medicine, and Dr. Alton Dooley, Jr., assistant curator of vertebrate paleontology at VMNH, suggest that the baleen whale was likely a benthic, or bottom feeding animal, primarily obtaining its food from scooping mud from the ocean floor and filtering the sediment from the plentiful fauna living in the sea floor. Such behavior is common in today's gray whales and to a lesser extent in humpback whales. The size and placement of a fracture on the left side of its jaw suggests that the injury likely had occurred during feeding. The characteristics of the injury indicate it was likely the result of a severe impact, likely trauma resulting from benthic feeding.
Supporting this theory is the density of the whale's rib bones. Dense ribs like those seen in this baleen whale are associated in bottom feeding in some other marine mammals, such as the manatee. Moreover, the presence of similar dense ribs in early baleen whale relatives suggests that baleen may have originally evolved to allow feeding from seafloor mud and only later was adapted for capturing fish and shrimp.
In addition, the publication documents the presence of lateralization in a fossil whale for the first time. Lateralization, or handedness, is well-known in humans and occurs in many animals, including modern gray and humpback whales. Like humans, whales are usually right-handed, and primarily feed from the right side of their mouths when they canvas the ocean floor. Such a fracture on the left side of the fossil whale's jaw indicates it favored eating from its left side, a much less frequent occurrence.
The museum has recently made select installments of the Jeffersoniana series available for free download from the museum Web site in an effort to make the scientific research of the museum's full-time curators more widely accessible to the public. Currently, the museum offers editions 17 to 20 of Jeffersoniana as free online downloads, with additional installments planned for release soon. Hardcopy versions of all museum publications are available for purchase from the museum's online store.
Visit www.vmnh.net or call 276-634-4141 for more information.