The giant pineal 'eye' of Platycyclops

The answer to the the little photo quiz was as the title suggests the relatively enormous pineal foramen of the oudenodontid dicynodont Platycyclops - so kudos to Matt. Quite why these dicynodonts have such enormous pineal openings is an unanswered question. Modern mammalian pineal glands are buried deep in our grossly inflated brains but are still used to regulate day/night cycles and seasonal cycles. In mammals it is influenced indirectly by exposure to light via signal that originate from the retina. In other vertebrates with a pineal foramen direct exposure of the pineal itself triggers the pineal gland to secrete its regulatory hormones. Pinealocytes have a strong resemblance to retinal cells and it is certainly tempting to speculate that the pineal organ of Platycyclops and related dicynodonts had crude image forming abilities. The forward tilt of the opening certainly gives the impression of a third 'eye'.
Googling around for information turned up one other little factoid, the name Platycyclops Broom 1932(the dicynodont) is a junior homonym of Platycyclops Sars 1914 (a copepod crustacean). As far as I know no-one has proposed a replacement name for the dicynodont.

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.