Possible Eobalaenoptera jaw

The SEAVP conference is coming up next month, and I’ve been spending most of my time trying to get that organized, including preparing my own presentation. I’m going to be speaking on Eobalaenoptera material that wasn’t figured in the 2004 description of the genus, including both type material and referred specimens.

One of these specimens is the jaw shown above. I’ve already talked about this specimen a few weeks ago, including why it’s only tentatively referred to Eobalaenoptera. I’ve finally finished the major part of the restoration work, and it’s now looking much nicer.

Now that the restoration is completed, another possible oddity has become apparent, as is visible in the dorso-posterior view of the jaw:

The right end of the specimen in this view is the anterior tip of the dentary, and it’s sitting so that it’s oriented vertically. That puts the mandibular condyle (the part that articulates with the cranium) in the foreground at the left. Note that the long axis of the condyle is not oriented vertically, but rather is angled about 45 degrees clockwise relative to the anterior end of the dentary. I’m pretty sure this isn’t due to deformation of the jaw; this seems to be the correct orientation.

This seems to be pretty unusual. Our Diorocetus specimen from Carmel Church has the long axis of the condyle and the anterior end of the dentary oriented in the same plane (that is, they’re parallel to each other). This is also true of Balaenoptera (at least, the minke whale, Balaenoptera acutorostrata). So, whatever this jaw belongs to, it seems to have a somewhat unusual jaw shape.

On top of that, going through the collections this morning I came across fragments of another large jaw from the upper Calvert Formation, but from the Potomac River. It’s almost as large as the Carmel Church jaw, but the shape of the condyle is very different, suggesting that there might be at least one other Eobalaenoptera-size whale in Calvert Bed 14.

***

This blog is now near (or perhaps over, I’m not sure) 200 entries, which can make it hard to find things in the archives. The iWeb software that I use to write the blog unfortunately doesn’t have a provision for searching or indexing entries. What I’m doing instead is adding some links on the bottom right of the home page to a custom topic index, to make it easier to find past posts. I’ve already added links for Carmel Church, Wyoming, and Solite excavations, and I’ll be adding more as I have time (for example, I’ll be adding basic geology, and visits to other museums). If there are particular categories you would like to see included, put them in the comments and if I can I’ll add them.

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4 Responses to Possible Eobalaenoptera jaw

  1. Jeff Sparks says:

    Hell Butch,I donated a jaw to the Calvert Marine Museum two years ago that looks very similar.You may want to ask Stephen if you can have a look at it.Good Luck,Jeff

  2. Boesse says:

    First off, very neat mandible! This looks similar in some minor ways to a mandible figured by Kimura (2004) – purely in the construction of the condyle, ventrally-ish deflected angular, and the cavernous mandibular foramen. In fact, that has got to be the largest mandibular foramen I’ve ever seen in a balaenopterid. The rotated condyle is also very strange.

    Very neat! It is difficult to tell, but is the anterior third rotated at all (i.e. counter-clockwise on a left dentary). Interestingly enough, all mandibles I’ve seen of Herpetocetus show an anteriorly-rotated dentary to a degree similar to extant Balaenoptera spp., which seems to indicate convergence in feeding behavior. I can’t remember which (functionally speaking now) rotation type (i.e. alpha, beta, etc.) it benefits during lunge feeding – I’m thinking of the type where the axis of rotation is along the long axis of the mandible. In any event, for other readers, it is postulated to be an adaptation for expansion of the oral cavity during feeding.

    I’m currently writing up a short paper about some very early (tortonian) Herpetocetus-like dentaries, so I’ve been thinking about this a bit lately.

    Bobby

  3. Brian Beatty says:

    For a basin this far inland, this fauna sure has a bunch of different mysticetes! Maybe a future blog entry could be some of the ideas we discussed last year regarding the geology and physiography of the Carmel Church locality? I know you’ve discussed Carmel Church a bunch, but the site is really fascinating.
    For other ideas, maybe an entry on comparing terrestrial mammal faunas of the East coast? I’d be happy to contribute some figures and data.

  4. Alton Dooley says:

    Brian, I sometimes think we’ve got some kind of wierd Star Trek-like telepathy connection. I’ve been thinking about doing an entry on Carmel Church baleen whale diversity. I’ve even laid out some of the specimens to photograph them. I’m pretty sure I can demonstrate at least 5 genera of mysticetes there, maybe 7.

    I’d love to have you do some guest blogs on east coast land mammals! There’s certainly plenty of them to talk about.

    That’s interesting about the dentary from Japan, Bobby. I do think that the Carmel Church mandible likely was rotating longitudinally, and I agree with you that herpetocetines were probably doing the same thing (probably convergently).

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