Friday, March 3, 2023

Updates from the CCNHM Lab 4: further reassembly of our basilosaurid whale mandible

Since I last wrote about preparation of "Elizabeth", the basilosaurid whale we collected during winter 2020-2021, our preparators have been banging away on it - and Ann-Frances has really exposed quite a bit of new mandibular material. Nearly all the large bones that were obvious in the limestone plaster jacket have now been removed, and it's pretty clear the entire left mandible was busted up by the mine equipment and was lightly re-cemented prior to discovery. There is still some hope that there might be some intact bone further down in the jacket.


The lower left P3 (third premolar) of Elizabeth, our as-yet-unidentified basilosaurid whale, still embedded in a chunk of the mandible.

 The fragment of jaw with a beautiful in situ posterior premolar has turned out to be the the left lower third premolar (P3) - mildly disappointing that it's not part of the maxilla, but this is good for two reasons: 1) it means that we now have a complete series of premolars in the left mandible, along with two molars; the right mandible has at least two molars, either all three of them or possibly just the P4 through M2. 2) It also means that there is still hope that the maxilla is in one piece somewhere in one of our jackets: if a fragment of maxilla was in this mandible jacket, we'd have an even worse puzzle to put back together.

 The exploded-view of the left mandible and premolars - we're waiting on some smaller fragments and won't glue any of these back in place until after we've photographed (and photogrammetized!) everything.

We also have evidence of at least two sets of teeth - there are some sub-millimeter thin partially formed enamel crowns that are hollow. These would almost certainly have to be permanent premolars, as there are already lower molars that have roots and thicker enamel - and might suggest that the premolars stuck in the jaw are milk teeth.

The fragments and teeth jigged up into position - I was focused on the teeth so I did not stick the coronoid process in place.

And here's a closeup of the premolars - what a beauty!

Now I would be remiss if I didn't speculate more on the identification. These teeth to me are looking to me so far to most closely resemble Dorudon serratus. This is great news because the holotype looks like someone blew it apart with dynamite (and also doesn't preserve any mandibular teeth). This would considerably expand the hypodigm (sample) of the species. However, I haven't yet done any serious comparisons with the type material and it's possible the comparative specimens we have at CCNHM are not identified properly. I'll have to double check Mark Uhen's (2013) basilosaurid review again!

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