Left-handed whale died a painful death

I’m back in Martinsville for a couple of weeks, but I’ll be back at Carmel Church soon. One of the reasons I returned is because of the release today of a new paper by Brian Beatty and me on one of the whales from Carmel Church.

The whale discussed in the paper is the same Diorocetus specimen we’ve been preparing since the museum opened in 2007 (search the blog for “Sinistra” for a history of posts about this whale).

Basically, this is a fleshed-out version of the talk we presented at the 2008 SEAVP meeting. The outstanding feature of this whale is the devastating injury that it suffered to it’s lower jaw, in which the left dentary was snapped completely in half:

The break occurred while the whale was alive, and the whale survived for some time after the break occurred. The break actually became infected, with pitting caused by abscesses:

The bone also began healing, with secondary bone growth over the break (more easily visible in X-ray images):

The whale has other injuries as well. The tip of the left premaxilla was crushed, and also partially healed (from left to right: left dorsal view, right dorsal view, right ventral view, left ventral view):

The left glenoid fossa and postglenoid process of the squamosal (the lower jaw articulation) also appear to be damaged (anteroventral view of the left and right squamosals; these should be mirror images of each other):

All this suggests that the whale suffered an almost head-on collision on the left side. The premaxilla was crunched and the dentary jammed back into the jaw joint. The curved dentary responded to the collision by flexing outward until it snapped. The dentary was actually shortened by several centimeters because of the break.

Brian and I believe this occurred when the whale was engaged in bottom feeding. This is a practice employed by modern gray whales, in which they scoop up a mouthfull of sediment and filter out the invertebrate animals living in it. The whale presumably collided with something hard on the seafloor, causing the injury.

We think that the jaw pieces never rejoined because the whale kept attempting (probably unsuccessfully) to feed. Every time it opened its mouth, the broken ends of the dentary shifted, preventing the injury from completely healing. Likely unable to feed, the whale would have eventually starved, or (more likely) weakened to the point that it was vulnerable to predators such as sharks. The rest of the skeleton indicates that the whale was a mature adult, with no evidence of arthritis or other age-related degenerative diseases, so it seems it was an otherwise healthy whale.

The injury has an additional interesting implication, in that modern gray whales are handed (or, more scientifically, lateralized). Basically, gray whales only feed from one side of the mouth. In right-handed whales, which make up about 80% of the population, the baleen plates are more worn on the right side. The fact that the Carmel Church whale’s injury was on the left side indicates that it was a left-handed whale.

Here’s a reconstruction of the moment the injury occurred (drawing by Michael Morriss):

There is actually an independent line of evidence that this whale was a bottom-feeder. It had remarkably dense, osteosclerotic ribs, in which there is very little cancellous (spongy) bone in the rib’s interior:

This is reminiscent of the ribs of sirenians, which have no cancellous bone in the ribs at all. In sirenians, this has been interpreted as ballast to aid the sea cow is staying on the bottom while feeding on sea grasses.

To document the relatively high rib density in Diorocetus, Brian and I measured rib thicknesses in a variety of whales, and found that the Carmel Church Diorocetus did have remarkably dense ribs compared to its contemporaries. To our surprise, however, we found that very early (Oligocene) baleen whales, as well as Oligocene toothed mysticetes such as Aetiocetus, have ribs as dense as, or more dense than, Diorocetus. If our assumption that high rib density correlates with bottom feeding is correct, it suggests that baleen originally evolved as a mechanism for benthic feeding. The use of baleen to capture swimming animals such as small fish and krill in the water column (employed by almost all living baleen whales) may be a behavior that evolved later.

One final note, not included in the paper. What exactly did this whale collide with to cause such an injury? Our assumption was that it was a rock on the sea floor, buried in the mud where the whale couldn’t see it. Big rocks are certainly not something we typically see in the silts and clays of the Calvert Formation, but there is one place we know of where the Calvert sea floor was littered with large rocks – Carmel Church:

It’s an intriguing thought that this whale may have injured itself trying to feed at Carmel Church. We know that it lived for probably weeks after the injury occurred, which would mean it didn’t leave the immediate area.

The Virginian-Pilot has a nice article about this paper and our Carmel Church activities:

http://hamptonroads.com/2009/08/fossil-whale-offers-clues-feeding-handedness

The paper was published in Jeffersoniana, and is available as a free pdf download. The full citation is:

Beatty, Brian L. and Alton C. Dooley, Jr., 2009. Injuries in a Mysticete Skeleton from the Miocene of Virginia, With a Discussion of Buoyancy and the Primitive Feeding Mode in Chaeomysticeti. Jeffersoniana 20, 28 pp.
Advertisements
This entry was posted in "Sinistra", Carmel Church mysticetes, Carmel Church Quarry, Chesapeake Group and tagged , . Bookmark the permalink.

10 Responses to Left-handed whale died a painful death

  1. Doug says:

    Very interesting. See, this is why i love pathologies like this! they tell a story. It sounds very painful indeed. Is that a rock? It almost looks like a hunk of bone.

    Also interesting is the density of the ribs. Is that an adaptation for bottom feeding? There’s a new species of whale known from San Diego (as yet unnamed, but a new species) that is beleived to be the ancestor of the gray whale. They explained in the exhibit how to tell feeding behavior in whales from their skulls: flat and broad were “gulpers”, narrow and arched were “skimmers”. They stated that based on bones we may not be able to tell if the new whale was a bottom feeder like it’s descendant. But if dense ribs are an indicator of bottom feeding, then maybe we need to take a look at the ribs.

    I showed this to my friend (who is really into whales) and she was blown away not just by the “left-handedness”, but also that baleen may have originated as a means for bottom feeding. great stuff!

  2. Alton Dooley says:

    That is a rock sitting next to Tim. Rocks that size aren’t uncommon at Carmel Church.

    In sirenians at least, osteosclerotic ribs have been interpreted as adaptations for benthic feeding. We don’t know if gray whales have osteosclerotic ribs like Diorocetus (we couldn’t find a broken rib, and didn’t have access to one we could saw in half).

    One issue with the gray whale is that it may be a benthic feeder secondarily. Various studies have indicated that gray whales are either very close to the balaenopterids (which I agree with) or close to the balaenids. Either way, benthic feeding in the gray whale may be a reversal (assuming we’re correct and benthic feeding is the primitive condition). If that’s the case and gray whales adopted this behavior recently, they may not show many benthic specializations. But it would sure be interesting to see how dense the ribs are in the gray whale lineage.

  3. Doug says:

    Well, if a gray whale washes up on one of the local beaches, i’ll try and get you a couple ribs. 😉

    Seems like it would have taken quit a bit of force to break that jaw. Do gray whales feed by just scooping out the sea bed, or do the swim into the sea bottom head first?

  4. Alton Dooley says:

    That’s tough to say. In modern whales, broken jaws have occurred because of ship collisions–obviously not likely in the Miocene! We didn’t see an injury like this in gray whales at USNM, although there was one specimen that hinted at a possible healed mandibular injury.

    The combination of the damaged premaxilla and dentary, as well as the nature of the break itself, indicates that the injury occurred due to a head-on collision (offset to the left). What’s out there to collide with? Other whales are certainly a possibility, and certainly baleen whales occasionally have rather violent interactions (although I haven’t heard of instances of head-on ramming). But in this case we also have the osteosclerotic ribs, which independently suggest benthic feeding. That’s largely why we prefer a bottom collision for the cause of the injury.

  5. Doug says:

    Sounds like we need to do more research on modern gray whales then.

    The only instances i have heard of whales head-on ramming something is sperm whales ramming whaling ships back in the day. Interestingly, gray whales earned the nickname “devil fish” because of their ferocity during the hunt.

    And maybe a point of clarification, how do osteoscleorotic ribs aid in benthic feeding? I am just curious on the details. I wonder if walruses have osteosclerotic ribs, but their mode of benthic feeding is different to that of a gray whale, so maybe not.

  6. Alton Dooley says:

    The osteosclerotic ribs just make the animal more dense; presumably less energy expended to remain on the bottom.

    IIRC, a captive killer whale was killed at Sea World some (10+) years ago during an intentional ramming incident with another whale; I seem to recall that the rostrum broke. Sorry, I don’t remember where I heard all this, so I can’t actually confirm it.

    I’ve heard anecdotal stories of dolphins killing sharks by ramming them. And, as you mentioned, there was the instance of the sperm whale sinking a whaling ship.

    There are some odontocetes which are benthic feeders as well. Certain populations of bottlenose dolphins will pull prey out of the bottom; in fact, they push up to 1/3 of their body length into the sediment. Odobenocetops was presumably a benthic feeder, given its similarities to walruses; I don’t think its postcranial skeleton is known. But in general odontocetes seem to have much lighter ribs than mysticetes.

  7. Doug says:

    Well, i sent an inquiry to the Los Angeles Museum. Let’s see if i get a response. The question i was asking was if the San Pedro Gray Whale had osteosclerotic ribs. I asked if they knew or if we had a way of knowing. The San Pedro Gray Whale is the only known fossil gray whale, from the Pleistocene.

  8. Grenda says:

    Last year Dr. Godfrey took the paleo volunteers to the National Geographic Museum in D.C. to see an exhibition on cetaceans. I can’t remember the country that was responsible for the exhibit but I did see a number of videos that showed the different types of feeding methods. I didn’t realize until then that whales bottom fed by siphoning; amazing video. I’ve tried to find the reference but have not succeeded thus far.

  9. Alton Dooley says:

    It’s possible that the ribs would have to be measured to see if they have more cortical bone than, say, balaenopterids. Osteosclerosis is relative; no cetacean has ribs that are as osteosclerotic as the sirenians, for example. We describe in our paper the measurements we used to compare the ribs.

    Baleen whales are surprisingly diverse in their feeding methods, particularly certain species (humpbacks, grays). Humpbacks do all kinds of things, including lunging, bottom feeding, bubble netting, and (I think) skimming.

    Yesterday I was looking at online images of whales feeding, and was struck by how lunge feeders (balaenopterids) also seem to frequently roll to one side when feeding (see, for example, the series of photos starting with: http://www.panoramio.com/photo/24938225). I’m not aware of studies on balaenopterids engaged in lunge feeding, but I bet they’re behaviorly lateralized as well (the one in the linked photo is feeding on the right side).

  10. Grenda says:

    If I ever find the video I will send a link. Thanks for the photo link.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s