Tyrannosaurus rex is by far the most famous of dinosaurs, a creature that looms large in the field of paleontology as well as in the media. This amount of attention has caused plenty of controversy but it has also resulted in many studies of various aspects of one of the largest and most well-known extinct carnivores ever to have lived, and a new paper in the journal Paleobiology by Snively and Russell examines the prospect of "inertial feeding" in this titanic terror.
Tyrannosaurus and its close relatives (i.e. Tarbosaurus, Albertosaurus, Gorgosaurus, Daspletosaurus, etc.) were definitely shaped by evolution in different ways than other large theropods, their skulls being their primary weapon. Fusion of the nasal bones and other adaptations allowed these dinosaurs to be bone-crunchers, large and powerful neck muscles contributing to the strength of the head that allowed them to deliver devastating bites to prey items. The function of such a powerful neck in feeding has often been overlooked, however, the impressiveness of the jaws and skull making it difficult not to be fixated on how they worked in and of themselves. As some have begun to notice, however, the musculature of the neck directly affects how a predator feeds and may open up the possibility of feeding techniques that may not immediately be apparent (see also McHenry, et al. 2007).
When a predator is at a kill, it's important for it to be mindful of its surroundings; fresh kills do not often go unnoticed for long, and even abandoned carcasses can still attract the attention of other members of the predatory guild. It would be advantageous, then, to be able to lift the head up and look around every once in a while to be sure that rivals were not getting too close. Likewise, being able to employ inertial feeding would be helpful, essentially lifting the head so as to throw the food to the back of the throat to be swallowed (or repositioned prior to swallowing) as seen in extant archosaurs such as predatory birds and crocodylians. Using these living evolutionary "bookends" as analogs may be helpful as the musculature in the neck of Tyrannosaurus seems to be a combination of features seen in birds and in crocodylians, allowing for direct comparison of the insertion points of various muscles.
Before the topic of neck muscles and feeding is addressed, however, it is important to note (as the authors of the paper do) that muscles play an important part in holding the head up in its proper position; all the muscles are not constantly at rest and at least some must help bear the load of the head. This could be a big problem in an animal with a sledgehammer head like Tyrannosaurus, but scars on the muscles indicate that it had many ligaments in its neck that helped support the massive head, although these did not entirely relieve the muscles of supporting some of the weight. Tendons also play an important role in the neck as the muscles can't always pull effectively between the origin and insertion points of the muscles, batteries of tendons acting like a "pulley system" to enhance the power of the muscle contractions.
Still, it's obvious that the head of Tyrannosaurus was it's main weapon in catching, killing, and consuming prey, and the new study appears to support the idea that Tyrannosaurus was not only able to strike quickly (the idea that it had to secure prey with its "meathook" arms first being refuted) but could also toss a 50kg piece of flesh and bone back into its mouth or even up into the air in a "toss and catch" technique. The fact that the ligaments of the neck supported most of the weight of the head allowed for this great range of movement and use of force, allowing the feeding habits of Tyrannosaurus to be more dynamic than just opening and closing the jaws.
As the authors note, however, more study of the biomechanics of Tyrannosaurus is needed, just as close relatives like those mentioned earlier in the post should be extensively studied in order to provide comparisons (and the large carcharodontosaurids should also be analyzed and compared to detect differences in feeding abilities). Likewise, the study relied on a lot of reconstructions and artwork, the authors suggesting that more rigorous methods of analyzing and reconstructing muscle groups be undertaken, and I was indeed impressed with the detail and forthrightness of this paper. Unfortunately I'm not as well versed in muscular anatomy or biomechanics as I probably should be, but please do yourself the favor or reading this paper. It reflects a very powerful, dynamic predator that was likely capable of taking live prey just as it was cracking the bones of carcasses it may have had the opportunity to steal or otherwise exploit. Tyrannosaurus just keeps getting more terrifying all the time...
McHenry, C.R., et al. "Supermodeled sabercat, predatory behavior in Smilodon fatalis revealed by high-resolution 3D computer simulation." PNAS, Published online before print October 2, 2007
Snively, E. and A. Russell, 2007, Craniocervical feeding dynamics of Tyrannosaurus rex, Paleobiology 33(4):610-638.
[Hat-tip to Vertebrate Paleontology Blog]
I'm gonna need that paper, Brian. :-)
Alternately, or in addition, could the large neck muscles have allowed shaking of smaller prey as a killing method?
Or even neck breaking manouvers with larger, long-necked prey?
I'm sure almost all theropods were able to do the shakedown, Cynic.
Zach; I'll send you a copy as soon as I can get a decent one myself. I had to make a PDF from the full text because I had a problem downloading it from BioOne.
Cynic; I'm sure the muscles could have allowed Tyrannosaurus to vigorously shake prey, but this question wasn't really addressed in the paper (it was more concentrated on supported the head and throwing the head back). The questions is, I would guess, what sort of forces shaking the head would inflict on prey/carcasses and if there was a more efficient way to do things. I imagine shaking would be a way to disarticulate/loosen up a meal, but there might have been other ways to accomplish that. As for a killing method though, I don't know; the force of the bite (especially if Tyrannosaurus was running when the bite was delivered, or otherwise moving quickly in an ambush attack) would have been like a freight train, so I wouldn't imagine that Tyrannosaurus would have shaken its prey unless the prey was relatively much smaller than itself (juvenile hadrosaurs?) where shaking would inflict a lot of trauma in addition to the bite.
Among living carnivores, shaking often outright kills prey items by snapping all sorts of bones and causing internal injuries. But you're right, Brian--shaking doesn't happen much with large animals. You never see lions shaking a wildabeest, but they do shake small animals to quickly kill them.
The neck muscles must have had a role in dismemberment, too. It's traditional to describe the teeth as "like steak knives", but that analogy only goes so far. Either she clamped large prey down with one hind foot, or relied on its own inertia; either way she would need to tear off sheep-sized pieces, as she lacked the scissor-like rear teeth we find in the big (heh) mammalian predators. No?
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