Carmel Church crocodile follow-up

Back on April 3, I reported that we had recovered a huge crocodilian tooth from Carmel Church (Thecachampsa or Gavialosuchus, depending on which worker you listen to). I’ve now had time to get that tooth back to the lab, clean it up, and compare it to the other teeth we’ve collected. As I suspected, it is the largest crocodilian tooth we’ve ever recovered at Carmel Church (above).

I noticed some other curious points in checking on this tooth. For many years the largest teeth known from the quarry were the two on the right above (the third tooth from the left is longer, but the fourth has a greater diameter). The second tooth from the right was only collected last August 10:

If you’ve been following this blog for awhile, you may have noticed that over the last several years we’ve been excavating a single small pit at the quarry. That means that these two gigantic teeth were found less than five feet apart! Here are all the crocodilian teeth recovered from this pit, over an area of perhaps 10X20 feet (I’ve excluded teeth that were clearly reworked):

I noticed when we collected the largest tooth that it has an unusual wrinkle in the enamel, that I suspect may be pathological:

When I showed these teeth to Brett, she noticed that the second largest tooth seems to have a comparable wrinkle in the enamel, although it’s less prominent and difficult to photograph. I strongly suspect that at least the two largest teeth come from the same individual crocodilian. As crocodilians have a variety of tooth sizes, I think it’s possible that several of the teeth in the photo able came from the same individual.

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6 Responses to Carmel Church crocodile follow-up

  1. 220mya says:

    Very nice teeth! However, isolated croc teeth such as these are not diagnostic beyond Neosuchia indet. They do not preserve any characters that are diagnostic of Thecachampsa/Gavialosuchus. Just because this is the only taxon thats been found in these age rocks in this area does not mean that the teeth *have* to be assignable to that taxon. Such an argument is circular reasoning.

  2. boesse says:

    That’s not exactly a problem until a more diverse crocodilian assemblage is established from the Calvert Formation, is it? If there’s only one taxon known up til now with teeth that big… well, the Chesapeake Group is fairly well studied and collected. If it hasn’t been found yet, well… don’t hold your breath. It’s a different story with Calvert cetaceans, some of which are still only known from fragmentary remains. However – with regards to large toothed, marine(ish) crocodiles that haven’t really been all that diverse in the Neogene – then I don’t really see that as a major issue. Besides, that’s always why the term “Cf.” was invented, after all.

  3. Alton Dooley says:

    Good points, 220, and I agree with you in part. Any referral based on limited material has to be taken with a grain of salt. However, there are two points I would make:

    My first reservation concerns the diagnostic value of teeth, particularly since Thecachampsa is a genus established on the basis of an isolated tooth. While Meylan et al. (2006) and Laurito and Valerio (2008) asserted that the isolated tooth of Thecachampsa is not diagnostic, they did not actually demonstrate this by showing that “Thecachampsa”-like teeth occur in multiple taxa that can be differentiated on the basis of other characters. I suspect that you’re correct that these teeth are not diagnostic, and that Thecachampsa at least should be a nomen dubium, but I think this has to be demonstrated. Admittedly, I don’t follow the crocodilian literature closely, but the most recent thing I’ve read on Thecachampsa was Laurito and Valerio (2008), and they did not make the comparison themselves nor did they cite anyone on the issue except Meylan et al. I’d like to see someone actually publish the comparisons (as was done with Scaldicetus by Kimura et al. (2006) and Bianucci and Landini (2006)).

    Second, I think that the _tentative_ referral of these remains to Thecachampsa/Gavialosuchus is reasonably justified (even if you include the caveat “most likely Thecachampsa” or something to that effect). As you point out, this genus (whichever name you call it) is the only crocodilian that has ever been identified from the Calvert Formation, or (I believe) from the entire marine Neogene along the Atlantic coast (not sure about Florida). This taxon is also well known and reasonably common, with several skulls and associated partial skeletons known. While the isolated teeth_could_ represent a different taxon, there is so far no evidence at all that there actually _is_ a second taxon present Calvert.

    I try to imagine a field biologist in a similar situation. Suppose our biologist is in Yellowstone National Park and finds a tuft of long, shaggy fur, too long to come from a bear. He (or she) would probably say the fur came from a bison, without any further consideration, even if the length and color of the fur is also consistent with a yak, and they would be justified in doing so.

    Now, if in their further explorations they came across a small population of yaks living in the park, they would be wise to change their initial identification, and state that “the fur came from some bovid, most likely a bison or a yak”. But in the absence of any evidence for yaks in the park, I think the “bison” identification would be justified.

    I realize I’m oversimplifying a bit with this analogy, but context is relevant to identification. To look at another hypothetical (and extreme) example, suppose that I found a tooth in the Calvert at Carmel Church that looked like Proconsul. I think that everyone would agree that I would be justified in initially rejecting the Proconsul identification and trying to find some other likely taxon for the specimen (preferably something known from North America), _based entirely on its geographic location_. If I chose to stick with the Proconsul identification, I would need to have extraordinarily solid and unquestioned evidence to back it up.

    All that said, at Carmel Church, and with these particular teeth, there may actually be more justification for suspecting a different taxon than for the Calvert in general. First, Carmel Church is a marginal environment for the Calvert; it’s nearer-shore and probably shallower water than any other Calvert locality. If there’s anyplace where a second crocodilian would show up in the unit, it would be Carmel Church. Second, these two (apparently) associated teeth seem really gigantic; I wonder what the size range of Thecachampsa/Gavialosuchus is (although croc growth styles make this problematic, at best). Third, I’m not convinced all these teeth are morphologically consistent with coming from a single taxon. The 4th tooth in the top image, for example, is distinctly different from the other teeth. It is much more laterally compressed, has more prominent carina, is shorter relative to is basal diameter, and may have thinner enamel for its size than any other croc tooth we’ve collected. Now maybe it still falls within the Thecachampsa/Gavialosuchus range; I’ve only looked at one associated dentition so far (which doesn’t seem to have a tooth that matches the 4th tooth above). So that brings us back to the first issue; how diagnostic are these teeth, really? I’d love to see a paper going through the associated dentitions of Thecachampsa/Gavialosuchus, demonstrating the diagnostic valve (or lack thereof), as well as the degree of heterodonty. Anyone game?

    And one final note: while I’m willing to use these specimens to generate likely faunal lists, I don’t think they should be used in taxon descriptions or in phylogenetic analyses, except in unusual cases where the limitations are clearly specified. Producing a faunal list is a different type of endeavor, and errors don’t carry the nomenclatural baggage that a mistaken species description does.

  4. Alton Dooley says:

    Or, what Bobby said.

  5. Alton Dooley says:

    I forgot to mention that this was my 300th post; nice that it’s generating some discussion!

  6. Doug says:

    Congrats on the 300th post!

    Yeah, nuts to the diagnostic power of reptile teeth. I know that the lateral compression of some teeth can distinguish them from others as xiphodonts, but that’s really about it. Why couldn’t they be more like sharks…

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