Tyrannosaurs "chewed" their food

[bh480@scn.org]

From: Ben Creisler bh480@scn.org

Tyrannosaurs chewed their food

In case the following story has not been mentioned here in 
all the excitement about tyrannosauroid feathers:
http://www.advancement.uark.edu/news/OCT04/UngarTRex.html

Researchers Take a Bite Out of Tyrannosaurid Eating Theory
A close look at the teeth of tyrannosaurids revealed to 
University of Arkansas researchers that these large 
carnivores may have eaten more like mammals than their 
reptilian cousins - by slicing and processing food with 
their teeth before swallowing it down. 
Newswise - Popular movies have shown Tyrannosaurus rex 
snapping up prey and swallowing it in great, ghastly 
gulps. But a close look at the teeth of tyrannosaurids 
revealed to University of Arkansas researchers that these 
large carnivores may have eaten more like mammals than 
their reptilian cousins - by slicing and processing food 
with their teeth before swallowing it down. This is the 
first time researchers have documented reptilians with 
eating habits that more closely resemble those of a mammal.
University of Arkansas anthropology professor Peter Ungar 
and former graduate student Blaine Schubert worked 
together under a grant from the Jurassic Foundation to 
reconstruct the diets of tyrannosaurids. These giant 
carnivores - classified as reptilians, a term that 
encompasses both bird and reptile species - could have 
been scavengers or hunters. Ungar and Schubert originally 
started their research to settle that question.
In the process, however, Ungar and Schubert uncovered 
evidence that tyrannosaurids may have processed their food 
like mammals, rather than swallowing it whole like other 
reptilians. A paper detailing their findings has been 
accepted for publication in an upcoming issue of Acta 
Palaeontologica Polonica (APP), a paleontology journal 
headquartered in Poland. 
Modern reptilians eat differently from mammals, the 
researchers explained. For the most part, they swallow 
food whole, without chewing. They don?t have the same 
degree of muscle differentiation and jaw control that 
mammals have. 
?They use their teeth to kill and capture animals, or to 
pull plant material into the mouth,? Ungar said. ?They 
don?t break stuff down in the mouth at all. All digestion 
happens inside the body.?
Mammals, on the other hand, have complex jaw joints and 
well-separated jaw muscles, with teeth of different shapes 
to allow precise chewing. The act of chewing starts the 
digestion process by breaking the food down to be digested 
further in the stomach.
?Mammals start with a big chunk of food and end up with 
lots of little pieces,? Ungar said.
Reptilians and mammals process their food differently 
because they must maintain different metabolic rates. 
Reptilians are cold-blooded and rely on the sun to heat 
them so they can function. Because they don?t derive their 
own heat, their metabolic rate is about one-tenth that of 
mammals.
?They don?t require the same amount of energy from food to 
function,? Ungar said.
As warm-blooded creatures, mammals have to increase the 
efficiency with which their bodies break down food. Part 
of that process involves breaking food down in the mouth 
so stomach acids can work on it more quickly, and the body 
can get more nutrients from it.
Scientists have yet to determine conclusively whether 
dinosaurs were warm-blooded or cold-blooded creatures. 
Since tyrannosaurids are reptilians, however, logic would 
seem to dictate that they would swallow their food whole.
?This makes me pause and say ?Wow they?re breaking things 
apart in the mouth.? They?re either eating something big 
or eating something more efficiently,? Ungar 
said. ?They?re doing something different than what the 
typical crocodile does, for whatever reason.?
Ungar and Schubert started their research at the Museum of 
Natural History in Gainesville, Fla., where they studied 
the teeth of modern reptilians, including caimans, iguanas 
and Komodo dragons. They used microscopy to look at the 
scratches, pits and grooves on the teeth and compared 
these wear features to the known diets of the reptilians. 
None of the modern reptilian teeth showed the tell-tale 
wear facets that occur with tooth-to-tooth contact, 
indicating that the reptilians were not using their teeth 
to process food before swallowing.
Next Ungar and Schubert?s research took them to the Royal 
Tyrrell Museum of Palaeontology in Alberta, where they 
took high-resolution impressions of tyrannosaurid teeth. 
On these teeth, the researchers found wear facets with 
microscopic scratches all running in the same direction - 
something before only found in mammals.
?We believe at least some of these facets indicate tooth-
to-tooth contact,? Ungar said. ?It?s intriguing because 
the tyrannosaurids are the only group of reptilians we?ve 
seen this in.?
?We are now excited about looking for similar patterns in 
other carnivorous dinosaurs,? added Schubert.
Ungar and Schubert?s findings indicate that T-rex and 
other tyrannosaurids may have adapted specific physical 
features for slicing flesh. Other meat-eating dinosaurs 
don?t show the same features, making tyrannosaurids a 
specialized carnivore.
Ungar and Schubert?s research was just the first step in 
determining that they may have processed their food 
differently. Next, they plan to test the hypothesis that 
these creatures were specialized, bone-crushing carnivores.
?We?re looking at years of further research,? Ungar said.