Thursday, September 18, 2008

The last dicynodont

With so much going on I've had little time for blogging. Recently there was some discussion of the supposed Australian Cretaceous dicynodont (maxillary fragment of the specimen is pictured on the left) over at Chinleana. I'll add my two cents here rather than commenting there just to keep something ticking over on my blog. Randy Irmis made a startling comment that the consensus was that it was indeed a dicynodont. This is news to me, I had always thought that the identity of the specimen was always the weak part of the claim. I have to add that I've never seen the specimen myself. Randy goes on to add that because it was surface float it is the provenance of the specimen that is suspect. Here I have to add my voice in support of Thulborn's original assesment, whatever it was there can be little doubt that it came from the Cretaceous. As has been noted Australia is flat and rather geologically quiescent. The nearest Triassic rocks are many hundreds of kilometres away. Nor do these Triassic rocks have much in the way of dicynodonts in them anyway - just one beat-up quadrate from more than 20 years of intensive collecting in the Arcadia formation (the main fossil-bearing Triassic formation of south-eastern Queensland). When you are out prospecting in most parts of the world you almost never find fossils more than a few tens of metres from the formation that bore them (unless there is a transport mechanism such as a river). Australia certainly never had post-Triassic glaciations that can randomly transport objects over large distances. So if the morphology is definately saying dicynodont then hey, I'm prepare to accept this extraordinary claim. Indeed recently another clade thought to have died out before the end of the Triassic has been found to have survived until the Cretaceous (I can say no more) so survival of the Dicynodonts may not be so weird after all.


Christopher Taylor said...

Indeed recently another clade thought to have died out before the end of the Triassic has been found to have survived until the Cretaceous (I can say no more)


Will Baird said...


Categorically understated!

220mya said...

Ah, I see that shooting my mouth off has gotten me in trouble again.

Adam - to be fair, I never said the consensus was that it was a dicynodont, just that all of the dicynodont workers I've talked to about it (less than 5), were happy with identifying it as such. I've never seen the specimen, and I don't know how many of them have seen the specimen.

Don't be too quick to dismiss weird transport - I just heard about a case of a bunch of Cretaceous fossils being found in situ in a very flat area with Pliocene bedrock (and a Triassic unconformity below that), and no evidence of human disturbance. This should be published soon. My undergrad professor also told me he once found Cretaceous ammonites on the surface of Triassic bedrock, ~100 km away from their source. With human occupation in Australia going back at least 40,000 years, I can't discount the possibility of human transport either.

I don't think the lack of dicynodonts from the Arcadia Fm is a strong argument for the specimen being Cretaceous. New groups of clades are being found all the time in formations that have been studied for a long time. I sure never expected to find a Lagerpeton-like animal in the Chinle Formation - and that's in an area that's been collected extensively for 125 years!

I have no particular problem with a Cretaceous dicynodont. Afterall, we never expected temnospondyls and tritylodonts to extend as far into the Mesozoic as their records do now.

Ultimately, I think the REE test I suggested over at Chinleana is the only way to confirm this extraordinary claim.

Timothy-Donald-Morris said...

To put in my 2 cents, this this is diagnostically a Dicynodont. I've spoken to the co-author of the original paper, and there is no doubt in my mind. I have also seen the specimen on display.

The really interesting part is that the relevant diagnostic characters are there. Firstly, it has a tusk. Secondly, it has the distinctive shape of a Kannymeyerid maxilla. I should say that even without it being diagnostic, it would obviously be Kannymeyerid if it was a dicynodont.

Now, the real clincher for me is that it even has a PATHOLOGY that is found only in large dicynodonts. The "maxilary fossa" as it has been called. This has been recorded from Kannymeyeria in Karoo a number of times. It is a circular, pit-like indentation on the maxila that would be the result of a degenerative bone condition or infection. In this case, it is all too prominent, and in fact goes all the way to the root of the tusk.

And just some informed speculation, I think this pathology is indicative of the living animal, in all the examples. Either the maxillary tusk was used in pysical tussles, resulting in lesions etc from injury. Or perhaps even sexier, that the area above the tusk might have housed a "musk gland" that might have been prone to infection, from spreading pheremones. Maybe it was where there was a wart or callus, that would occasionally be injured.