Afternoon Terrors

This skull is not an exact replica of the skull originally unearthed and described under the name Abelisaurus. That skull was missing a good amount of the right side of the skull and the palate, the roof of the mouth, was fragmentary at best. Above the orbits where the eyes would be housed and along the nasal bone, however, we can see the rugosities and places where keratinous hornlets may have protruded upward from the skull. The mandibular fenestration visible here would have made the closing actions of the jaws extremely powerful as the muscles running through would have added additional strength to the closing of the mandible. An alternative theory, or perhaps secondary use, for a fenestra that large would be for thick bundles of nerves to be threaded through the hole. Why any animal would need that much nervous tissue in that exact placement in its skull I could not say though. Neither of these observations is published, to my limited knowledge of the moment, but it is quite possible these theories have been put forth by others as well.

Illustration Citation wanted

As mentioned yesterday, the lack of post cranial material makes designing the body of Abelisaurus in illustrations a special kind of difficult. Abelisaurus has been argued to be a middle of the family Abelisaurid and it has been argued to be a basal Abelisaurid; a third argument has potentially made it a closer relation to Carcharodontosaurus, and thus not an Abelisaurid at all, which presents an interesting reordering of the family. We do not want to worry about that sort of thing today though. Instead, let us look at the arms, one of the most characteristic and diagnostic post-cranial features of the Abelisaurids that we know of (including Aucasaurus, Carnotaurus and Majungasaurus). The arms of the known post-cranial skeletons are typically very reduced with the palms facing the ribcage of the animal and the fingers pointing toward the tail. That is not to say that this is the only way in which the hands of Abelisaurids were constructed and, if it is a basal member of the family named after it, Abelisaurus may not have arms like other Abelisaurids.

Illustration Citation wanted

If it did it would probably look a lot more like this version. The arms here are not very reduced, but they could be the start of the family trend of evolution where extreme reduction and a rear facing hand become common. That small arm could have been reduced in many other animals that we have yet to unearth or that we also only have the skulls, or very little post-cranial material for, with which to describe the animal. The legs on this illustration have an interesting ball of muscle at the calf, but a muscular calf is not as important to us in this discussion as the speculation about which way the arms faced and how they were held in relation to the body.