Tyrannosaurus Forelimbs Revisited

Earlier in the week, I posted some theories regarding the function of T. rex’s diminutive arms. I just thought I would add some recent research before I closed the topic:

Matt Smith (Museum of the Rockies) and Ken Carpenter (Denver Museum of Natural History) began examining the wrist, hand and finger bones of the T. rex forelimb and used wax to hold the bone joints together. This led them to figure out that the forelimb's two claws have an unusual feature: unlike the opposable human thumb and forefinger combo, which can grasp objects, the two dinosaur claws face away from each other like the barbs of a fishing hook.

What does this mean? Perhaps these claws embedded themselves into the prey’s flesh and immobilized it while T. rex used his jaws to finish the job. .

Matt Smith says, "People had been looking at [forelimb] function based on proportionate size. I don't think that's appropriate."

What were T. rex’s tiny little arms for anyway?

American palaeontologist Henry Osborn first described T. rex but initially expressed doubts that the diminutive arms he found belonged to this enormous animal. After investigating further and finding it to be true, he considered their purpose and advanced the first theory in 1906: that they were used as ‘graspers’ or stabilizers during copulation.

But this was only the start of a debate that still rages. In 1970 British palaeontologist Barney Newman suggested that the small arms braced the beast's body as it stood up.
Another, contrasting theory suggested that the small limbs are vestigials (degenerated organs that have lost their use).

To add to the confusion it seems that the muscular of the T. rex was very well defined and though the arms were disproportional to the animal's body, they were still very strong. So some people consider that the most useful function of the limbs was to be used as meat hooks while the animal fed. This theory is supported by the beautifully sharp claws on T. rex’s two fingers.

In contrast, Greg Erickson has recently commented on a biomechanical analyses of a new specimen. The aim of this study was to try and understand the physical capacities of T. rex's diminutive structures. Erickson has concluded that the elbow could not be extended beyond 90° and though the arms were very strong (they could lift about 180 kg or 400lbs) they had a very limited side-to-side and up-and-down motion.

It is also known that T. rex's arms were often broken (and mended) during its life, suggesting that the arms were poorly suited for their function that these animals could go without using their arms for extended periods of time.

I read an interesting theory a while back that suggested the arms were most useful in juveniles, as a counterbalance to the young dinsaurs fast quickly. The suggestion was made that the arms were proportionally longer in childhood compared to adulthood. However, as far as I know this theory did not gain popularity.

The truth is that no one knows the answer. Scientific inquiry into this issue has been going on for a century and it doesn’t seem likely that the mystery will be solved soon. If you have any other ideas, please let me know!

Ancient proteins link T. rex to chickens

Well I’m sure everybody has seen this sensationalist headline in the last week, instead of tackling the controversy myself, I’ve decided to list a few posts by bloggers who have already posted on the topic:

PZ Meyers of Pharyngula posts Stone soup; or, extracting protein fragments from T. rex bones

Brian Switek of Laelaps in his post, And the T. rex goes… cock-a-doodle-do?

Mike Ryan of Palaeoblog posts T. rex Protein Sequenced

And the original article:
Analyses of soft tissue from Tyrannosaurus rex suggest the presence of protein. 2007. Science 316: 277 - 280

In the News...

Big news in palaeontology this week, Graeme Lloyd posts on yet another gliding reptile in This Life is a Fiction, Matt Celeskey discusses Oryctodromeus, a burrowing dinosaur in his blog, The Hairy Museum of Natural History and Michael Ryan declares that T. rex Wins By A Nose in Palaeoblog.

Friday's Mystery Fossil Revealed

Congratulations to Mambo Bob for his response. Friday's Mystery Fossil was indeed a theropod and specifically a Tyrannosaurus but not Sue of the Chicago Field Museum. Rather, the picture is of a specimen at Palais de la découverte in Paris. Also, points Malacoda for his imaginative guess (an obvious asset in palaeontology:)

The image may be familiar to some as it was featured in my January posting, CSI: Garfield County.

Image copyright ©2005 David Monniaux.