Xiphiacetus from Carmel Church

A common question I get from the public is “How do you identify a species?”. It happens that I’ve been trying to make a lot of identifications in preparation for my SEAVP talk, so this seems a good time to give an example.

The skull shown above is the most complete odontocete (toothed whale) skull we’ve ever found at Carmel Church. The views, from top to bottom, are dorsal (top), ventral (bottom), left lateral (side), and right lateral. For many years, this type of long-snouted skull would have been referred to the European genus Eurhinodelphis, and in fact most museum displays will have these skulls labeled as Eurhinodelphis. In 2005, Olivier Lambert showed that some specimens referred to Eurhinodelphis actually had a quite different skull structure from the genotype, and erected the new genus Xiphiacetus for those specimens. As it turned out, most specimens, including all the North American ones, belong to Xiphiacetus, while Eurhinodelphis is only known from the North Sea Basin in Europe.

Xiphiacetus is probably the most common odontocete in the Calvert Formation, and it’s also the most common at Carmel Church, with a minimum of four individuals. But there are two species of Xiphiacetus known from the Calvert, X. bossi and X. cristatus. Which species does this skull represent?

When a new taxon is described, a required part of the description is the diagnosis, which is just a list of characters that make the new taxon unique. Here are the first two (out of six) characters that Lambert (2005) used to distinguish X. cristatus (p. 213):

“Emended diagnosis. This species differs from Xiphiacetus bossi in the following combination of characters: major thickening of the maxilla on the supraorbital process; posterior margin of the maxilla on the cranium notched by a forwards indentation of the frontal and the supraoccipital laterally to the vertex;…”

Both of these characters involve the maxilla, the bone that holds most of the teeth in the upper jaw. In whales, the maxilla also extends onto the top of the head (a condition known as telescoping). Here’s a larger view of our Xiphiacetus skull, in dorsal view:

And here’s an outline of the right maxilla:

(I’ve fudged this a little bit; parts of the maxilla were not preserved, and there are a few areas where the maxilla is only visible because an overlying bone is damaged.)

Lambert’s second character mentions a notch along the back edge of the maxilla, caused by a forward projection of two other bones (the frontal and supraoccipital). Zooming in on the posterior edge, that notch is clearly visible (left side of image):

Lambert’s first character involves a thickening of the maxilla on the supraorbital process (a projection of bone over the eye socket). That is best observed in lateral view:

Again, if we zoom in on the back of the skull we can see this thickening more clearly (outlined in red):

The notch in the maxilla is also visible in this view (the small red triangle in the upper left).

Using Lambert’s diagnosis, this skull is clearly an example of Xiphiacetus cristatus, rather than X. bossi.

What about our other Xiphiacetus specimens from Carmel Church? We have two other partial skulls, but neither is as well preserved as this one. Both have some thickening of the maxilla, but not as pronounced as in this specimen. The posterior margins of the maxilla are badly damaged in both specimens, and I haven’t yet been able to determine if they are notched. For now, they both have to be considered Xiphiacetus sp.

If you’re in Martinsville, the Xiphiacetus cristatus skull is on exhibit in the “Uncovering Virginia” hall.

Reference:

Lambert, O., 2005. Review of the Miocene long-snouted dolphin Priscodelphinus cristatus du Bus, 1872 (Cetacea, Odontoceti) and phylogeny among eurhinodelphinids. Bulletin de l’Institut royal des Sciences naturelles de Belgique, Sciences de la Terre 75:211-235.

***

I’m still making incremental changes to the blog, so you may see some experimentation with various things in the coming months. If you use the archive quick links, you’ll find that I’ve updated the Carmel Church page to include all my pages on the site, including individual specimens as well as excavation updates. (I noticed that just over 1/3 of my pages have been about Carmel Church; I think I need to write about some other things!)

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This entry was posted in Carmel Church odontocetes, Carmel Church Quarry, Chesapeake Group, Paleontological techniques and tagged . Bookmark the permalink.

7 Responses to Xiphiacetus from Carmel Church

  1. Tony Edger says:

    “I think I need to write about some other things!”

    Perhaps, but the Carmel Church postings are great reading. This one in particular hit home since a recent find of a tooth from an Orycterocetus crocodilinus along the Chesapeake Bay has prompted me to begin reading more about cetacean fossils. As an amateur at all of this, I find your explanation with its highlighted photos in this posting very nicely done. (By the way, your recent “non-Carmel” posting on Darwin and his reef theory prompted a posting on my blog — http://fossilsandotherlivingthings.blogspot.com/2010/03/glaciers-evolution-and-reefs-darwin-and.html.)

  2. Alton Dooley says:

    Cetaceans do have a way of sucking you in, Tony, so welcome!

    The truth is, I spend so much time working on Carmel Church that it will probably continue to dominate my thoughts.; there’s just so much there to work on! Though I will probably be doing a bit more over the next year on the Ordovician and the Carboniferous (in coordination with upcoming exhibits).

    I don’t know if you’ve searched the archives, but you might find this post on sperm whales interesting:

    http://web.me.com/dooleyclan/Site_2/Blog/Entries/2009/4/23_More_sperm_whales.html

    I had trouble getting the link to your post on Darwin to load (I think the problem was the final period). I’ve posted a corrected link below. Very nice summary of the Darwin-Agassiz relationship!

    http://fossilsandotherlivingthings.blogspot.com/2010/03/glaciers-evolution-and-reefs-darwin-and.html

  3. Doug says:

    This guy had an “overbite” right? If so then i saw his skeleton at the Smithsonian. Man, those odontocetes had some weird jaws (eg this one and that skimmer porpoise at the San Diego Museum).

  4. Alton Dooley says:

    There is a mounted skeleton of Xiphiacetus at the Smithsonian. As I recall (someone from SI correct me if I’m wrong), I think it’s a composite of two individuals; the skull and atlas was one animal, and the rest of the skeleton was a second one.

    The upper jaw is indeed quite a bit longer than the lower. This super-elongate rostrum evolved independently in several different odontocete lineages.

  5. JenatVisitorCenter says:

    Feel free to write about Carmel Church as much as you want! I thoroughly enjoy telling visitors of new finds. You should see their expressions sometimes.

  6. boesse says:

    That’s a beautiful skull – kinda neat how the premaxillae split like that; I’ve seen a similar post-mortem phenomenon with longirostrine delphinid skulls.

    I recently did a drawing of the Xiphiacetus skull/jaws at the USNM – I suspected that it was a composite, because the posteriormost teeth on the dentary are located a few inches anterior to those on the upper jaw – it looks like the jaw is from a much larger individual than the skull (thus making the “overbite” even longer than it appears on that mount).

    What’s the deal with all the eurhinodelphinid taxa that Myrick described in his ’79 dissertation? Has that passed the informal “statute of limitations” on unpublished theses?

  7. Alton Dooley says:

    As an unpublished thesis, I don’t think the taxa would be considered formally proposed, and I think the names would technically be available (anyone more up on the ICZN rules feel free to correct me). Regardless, Lambert cites Myrick’s dissertation, and placed those nominal taxa into synonomy with either X. cristatus or X. bossi, an opinion with which I agree.

    On the divergent premaxillae, the same thing also occurs frequently in Squalodon. There does seem to be some particular consistent feature that results in that post-mortem deformation.

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