Mysticete squamosal revisited

During our most recent Carmel Church excavation, we collected a squamosal (cheek and ear region) from a small baleen whale (above). Since returning to the museum I’ve had a chance to clean this specimen and compare it to other bones in our collection.

Possibly the single most useful bone in identifying fossil whales is the petrosal, one of the earbones. The petrosal is almost complete in our new specimen, and we have petrosals from several other Carmel Church whales in our collection for comparison.

One petrosal in our collection immediately stood out as a very close match; none other than “Sinistra”, our Diorocetus specimen with the broken lower jaw. In the image below, “Sinistra’s petrosal is at the bottom; the bone projecting to its right is the posterior process of the petrosal, which is embedded in the squamosal of the new specimen:

Here are some more views of “Sinistra” and the new specimen:

These bones are very similar to each other in both size and shape, even though the squamosal in the new specimen is smaller than in “Sinistra”. If these are both Diorocetus, it’s possible that the new specimen is a younger individual, as whales may exhibit allometric growth in the petrosal relative to the squamosal.

One more photo, just to make an interesting contrast:

The bone on the left is the squamosal of “Caroline”, the type specimen of Eobalaenoptera harrisoni, beside the new squamosal. While they’re from opposite sides of their skulls (“Caroline’s” squamosal is the right side, while the new specimen is the left), the level of preservation is comparable (the new specimen is actually somewhat more complete). “Caroline” is the largest whale we’ve ever collected from Carmel Church, while the new specimen is one of the smallest, so this makes an interesting contrast.

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3 Responses to Mysticete squamosal revisited

  1. Bobby says:

    Beautiful! Appreciating the mysticete petrosal is an acquired taste, in my opinion. They’re just so weird looking. I’m fairly well familiarized with cetotheriid and balaenopterid petrosals, but It’s going to take a while to really appreciate the diversity of petrosal shape within “cetotheres”. That posterior process looks fairly short – obviously not as short as in herpetocetines or eomysticetids.

    Very nice find! Keep your eyes peeled on coastal paleo for similar find I recently made.

  2. Tony Edger says:

    I went back to your entry for day 10. Makes for great reading juxtaposed with this current entry. Thanks.

  3. altondooley says:

    Thanks, Tony.

    Bobby, I think the posterior process is quite short in most of the cetotheriids s.l., although, as you say, not so much as in Herpetocetus (like the one you figured on your blog recently). A long posterior process is present in the balaenopterids (and Eschrichtius), Eobalaenoptera, Aglaocetus, balaenids (at least the ones I’ve looked at), and IIRC, Pelocetus.

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