A question about some anatomical features of a couple of permian Synapsids

[Loon]

I was looking at my CollectA Dimetrodon and Estemmenosuchus and had a couple of questions about the anatomy of these animals.

First, with the Dimetrodon, are the tips of the sail actually exposed bone, or keratin? I remember hearing something like this but was not sure.


Secondly for the Estemmenosuchus, the "antlers" seem to be implied as distinct from the rest of the face, like in deer. But, is this really the case?


Just figured I'd ask here, thanks in advance for your replies.

[Newt]

The Dimetrodon sail is supported by some evidence. The tips of the spines in some specimens of D. giganhomogenes are irregularly curved and twisted "like the fingernails of the senescent Howard Hughes," in the words of the researchers. This makes it unlikely that these tips were supported by the web of the sail. They would probably have been covered with some form of skin; exposed bone is surpassingly rare in vertebrates (AFAIK only present in deer after they've shed the velvet from their antlers, and in certain amphibians such as ribbed newts and gladiator treefrogs that protrude sharp bone through their skin as a weapon), and there seems to be none of the heavy vascular imprning on the bone associated with keratin covering. I don't know if anyone has looked closely at the other species of Dimetrodon to see if they have the same spine tip morphology.


Rega, E. A., Noriega, K., Sumida, S. S., Huttenlocker, A., Lee, A., & Kennedy, B. (2012). Healed Fractures in the Neural Spines of an Associated Skeleton of Dimetrodon: Implications for Dorsal Sail Morphology and Function. Fieldiana Life and Earth Sciences, 5, 104–111.


I haven't read much about Estemmenosuchus, but looking at this skull image, there seems to be some increased rugosity on the horns. They're certainly not separate, deciduous bones like in deer (again, deer are weird), but they probably had some kind of tougher soft tissue on them than the rest of the face.