So having covered the fact that tyrannosaurs were both predators and scavengers in yesterday’s post, we can now talk about how they were feeding. Previous records of feeding by large tyrannosaurs have tended to show a pretty rough approach – bite bites going deep into the bones which are sometimes part-dragged out leaving scores in the bone. This is no great surprise, they have big and robust teeth, and huge skulls with a lot of muscle power behind them and a powerful bite. It makes sense that they can be quite careless as it were in their approach – when you have a bite that can break pretty much anything open then go ahead and bite.
Tyrannosaur scrape marks left in a Saurolophus humerus. From Hone & Watable, in press.
This is however, not what we see here with the Saurolophus specimen. The humerus has suffered a large number of bites, but most of them are shallow, not big deep gouges. What’s more the marks are far from randomly distributed across the specimen. There are some relatively big and deep bites at the ends of the bone, but along the low and flat deltopectoral crest (where the main muscles would attach) the marks are shallow and clearly made by teeth being dragged across the surface of the bone. It’s worth noting that the deep bites at the end were heavy enough that if they have been performed on the DP crest then this would have broken. In short, the animal was being relatively careful here when it was not at the ends.
Deep bites by a tyrannosaur on a Saurolophus humerus. From Hone & Watabe, in press.
What this shows therefore is that the tyrannosaur was making an active choice in how it fed on the bone. It chose to make heavy bites deep into the bone ends, but deliberately did not do this on the deltopectoral crest even though it could have done so. Tyrannosaurs did not just rip apart carcasses and crunch through bones even though they could. Sure on some occasions they did, but not always. They could, and did, chose how to feed and could be relatively delicate.
Differing feeding styles by Tarbosaurus. Image courtesy of Matt van Rooijen.
Why the different styles? Well the deep bites might have been to try and get to the cartilage on the bone to eat it, but might also have been to simply free the bone from the rest of the skeleton to make feeding easier. This is supported by the fact that the marks on the DO crest are on both sides but at different angles to each other. The different angles means that they were not made by the top and bottom teeth together in unison. That also means that the bone must have been turned over at some point for the Tarbosaurus to get to the other side, and thus the fact that freeing the bone from the rest of the body would have assisted feeding.
This specimen does then give us rather greater depth to our understanding of tyrannosaur behaviour both in terms of the practice of scavenging and in how they dealt with carcasses. This shows a surprisingly delicate touch by a 10 m and 6 ton* reptile.
* Note – vague, but probably not inaccurate estimate.
Hone, D.W.E., and Watabe, M. 2010. New information on scavenging and
selective feeding behaviour of tyrannosaurs. Acta Palaeontologica Polonica.
Artwork courtesy of Matt van Rooijen over at the Optimistic Painter. More superb work I have to thank him for.