Carmel Church kentriodontids

Kentriodontids are a family of dolphin-like toothed whales that were widespread in the Miocene. They are sometimes considered as the possible sister-taxon to the Delphinidae, the family that includes most of the living dolphins.

Kentriodontids are common throughout the Calvert Formation. There is a general trend within the family of an increase in body size over time, with tiny Kentriodon (less than 2 meters long) found in the lower Calvert and Hadrodelphis and Macrokentriodon (~ 4-5 meters long) found in the upper Calvert and Choptank, respectively. It should be noted, however, that there are apparently still a number of undescribed Calvert taxa that may disrupt this trend.

Kentriodontids are known from the Carmel Church bonebed, based on teeth, periotics, and a few bones. The most common remains are from a large species, consistent in size with Hadrodelphis and Macrokentriodon (as would be expected given Carmel Church’s age). In the image at the top, the two teeth on the left were associated with this mandible:

However, there are hints of a smaller kentriodontid species at the quarry. We have several periotic bones that appear to be from a very small kentriodontid (although I can’t yet rule out some other taxon):

The third tooth from the left in the top image was collected at Carmel Church on our last excavation. It is notably smaller than the large species, but it seems a bit large to go with the tiny petrosals.

There is an undescribed kentriodontid from the top of the Calvert, sometimes referred to as the “medium-sized kentriodontid”. We have a specimen apparently from that species that was collected a few years ago from Westmoreland County; its tooth is on the right in the top image. While its length is comparable to the Carmel Church specimen, the proportions and crown shapes are quite different.

I’m not sure what to make of this new tooth. Is it a separate medium-sized kentriodontid species? Or is it just a small individual of our large kentriodontid? I have to admit I lean toward the latter explanation, but we’ll have to see what else turns up in our material.

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10 Responses to Carmel Church kentriodontids

  1. Brian Beatty says:

    Could the tooth on the right be a posterior tooth of the same large kentriodontid taxa to the left? I’ll admit that it doesn’t look much like a posterior tooth of any odontocete I’ve ever seen, but it would be worth noting what we know about the changes in the toothrow from front to back in the known taxa first.
    I’m slowly trying to get a handle on odontocete dentitions, modern and fossil, but must admit to a bit of happy frustration. Frustrated because there are just too many, and happy, because there are so many! In the end, at least there is plenty of interesting work to do!! 🙂

  2. Alton Dooley says:

    Apparently when you blog on too little sleep, the first thing you lose is the ability to properly use contractions. Corrected for grammar mistakes.

  3. Alton Dooley says:

    The tooth on the right (the one from Westmoreland) is apparently from a smaller individual. We have a partial mandible, the cranial vertex, and a rib from that individual, as well as the single tooth (which was not in situ). The Carmel Church specimen includes a partial mandible and a number of teeth, and some ribs and vertebrae that questionable go with it.

    Based on a brief, non-quantitative glance at the mandibles, the Westmoreland mandible appears to be somewhat shorter and more gracile, with more numerous, more closely-spaced alveolae.

  4. Boesse says:

    So, I’ve got a question (there aren’t as many ‘good’ kentriodontids from the west coast, aside from what may be lurking in the bowels of LACM) – are there any kentriodontids without fused (or elongate) mandibukar symphyses?

    Kentriodontids and cetotheres sensu lato are two of the reasons I don’t do any collecting in assemblages older than Clarendonian/Tortonian; I’m not really sure what to make of either group (and their variable phylogenetic positions in different analyses).

  5. Alton Dooley says:

    Nothing older than Clarendonian? You wimp! 🙂

    The lack of a mandibular symphysis is generally considered to be a synapomorphy of the Mysticeti (or some subset of Mysticeti). Aetiocetus and other toothed mysticetes lack a symphysis; even Janjucetus did not have a sutured symphysis.

    I’m not aware of any odontocetes that lack a fused symphysis, and it’s usually an elongate one. As far as I know all the kentriodontids have a long symphysis.

    I would be curious, though, to see what the symphysis looked like in Odobenocetops, considering how short the rostrum is. I’ll have to look that up…

  6. Boesse says:

    I was more so referring to odontocetes which have a short symphysis, and fused poorly enough so that they can disarticulate easily. Maybe I should have said ‘firmly ankylosed’ instead of fused. I.E. some delphinids, extant phocoenids, monodontids, etc. have relatively short mandibular symphyses, as opposed to the condition in eurhinodelphids, (most) pontoporiids/lipotids/iniids, etc. It seems that many ‘kentriodontids’ have fairly elongate symphyses (i.e. >1/5 of their mandibular length – educated guess, I’m probably off by a bit).

  7. Alton Dooley says:

    That may be a function the length (or length:width ratio) of the rostrum. Eurhinodelphids and pontoporiids have very elongate rostra. That’s generally true of kentriodontids as well, although my impression is that the rostrum is relatively more blunt in Kentriodon than in the large taxa. I haven’t seen separated dentaries in a kentriodontid, but I haven’t looked at that many of them.

    Squalodontids also have very elongate rostra, and a very long symphysis that typically overlaps the first 8-9 teeth. The dentaries are almost never separated, but they do on occasion. I’ve seen at least 2 that have separated. One may have been a juvenile, but the other was a large adult specimen.

    Physeteroids also have elongate rostra and long symphyses. Even so, the two specimens we have at VMNH both have separated dentaries.

  8. Brian Beatty says:

    The “platanistids”, Pomatodelphis inaequalis and P. bobengi also have long rostra, but I’m not sure their symphyses are quite as long (proportionally) as those of the others mentioned. Goniodelphis definitely has an elongate symphysis, but jam packed with large teeth too.
    It’s funny – I hesitate to work on anything younger than Clarendonian for the same reasons you’re avoiding it, Bobby. Well, really it’s because I am more familiar with them because of FL localities I grew up with. As much as I should know better than to dive into such a mess, I am really getting into the late Oligcocene and Early/Mid Miocene odontocetes, they are really quite interesting! Now if only I could live another 100 years so I have a chance of getting somewhere with them….

  9. Boesse says:

    I figured it was a function of rostrum length; I must say, I totally forgot about Delphinodon – it has a really short rostrum for a kentriodontid, and also a very short symphysis (comparable to a longirostrine delphinid). So, nevermind, I answered my own question!

    Besides taxa being very familiar, there are anough post-Middle Miocene units in Central and Northern California to keep me busy for another decade (not including the volume of material I’ve already collected).

    Thanks for the marine mammal post! It’s probably no secret that these are my favorite posts on here.

  10. Alton Dooley says:

    I’ll try to keep some more marine mammal stuff coming, in that case!

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