Monday, July 01, 2013

Did Tyrannosaurus use its "vestigial" limbs in a feather display? 

Here is an artist's illustration of a recent find of a feathered Tyrannosaur found in China:

The article in Wired magazine.

The small limbs of T. rex have long been a puzzle. Various functions have been proposed for these comparatively small limbs, and it has also been suggested that they are vestigial. Some suggestions are discussed here.

Another possibility that recently occurred to me was that the small but powerful arms could have been used in signalling or display using feathers. "Grendel's Father" writing here has a similar suggestion, "If the arms of large tyrannosaurids bore display feathers of some kind, this could partially explain the paradoxical small size plus heavy musculature (perhaps employed in some kind of flapping display?)"

The reconstructed ancestor of T. rex above certainly looks like it could be about to wave its little arms to show off its arm feathers. Something is known of the likely range of movement of these forelimbs, and this might help address how likely it is that the arms were used in a flapping motion. (My wife Karna O'Dea suggested that feathered arms could also have aided in balance.)

Also (to be really radical) did flapping displays evolve into flight in birds? Here is an article "Tyrannosaurus rex protein proves dinosaurs evolved into birds." And another article on the same theme.

Here is a picture of a South American bird, the hoatzin, which is described as "a chicken-sized relative of the cuckoo bird that can’t fly very well and smells like cow manure". It can however do a nice display with its wings:

One hundred years of T. Rex: commentary from Tetrapod Zoology blog.

From Wikipedia:

"Tyrannosaurus rex forelimb bones exhibit extremely thick cortical bone, which have been interpreted as evidence that they were developed to withstand heavy loads. The biceps brachii muscle of a full-grown Tyrannosaurus rex was capable of lifting 199 kilograms (439 lb) by itself; other muscles such as the brachialis would work along with the biceps to make elbow flexion even more powerful. The M. biceps muscle of T. rex was 3.5 times as powerful as the human equivalent. A Tyrannosaurus rex forearm had a limited range of motion, with the shoulder and elbow joints allowing only 40 and 45 degrees of motion, respectively. In contrast, the same two joints in Deinonychus allow up to 88 and 130 degrees of motion, respectively, while a human arm can rotate 360 degrees at the shoulder and move through 165 degrees at the elbow. The heavy build of the arm bones, strength of the muscles, and limited range of motion may indicate a system evolved to hold fast despite the stresses of a struggling prey animal. Carpenter and Smith dismissed notions that the forelimbs were useless or that Tyrannosaurus rex was an obligate scavenger.[58]"

Relevant article on T. rex as predator.


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