While a Tyrannosaurus rex’s arms seem puny and pathetic, they may have been used as vicious weapons that enabled the fearsome dinosaur to capture and kill its prey.
Why did the T. rex have such small arms?
Different scientists had different ideas about how T. rex arms functioned. Some suggested that the dinosaur may have used its arms to push itself off the ground into a standing position. Others suggested that the thin, short arms, may have been helpful in holding onto mates during sex. There were still others who also suggested that the T. rex may have used its arms to hold onto its prey. Meanwhile, some scientists also suggested that T. rex arms, tiny as they were, were probably vestigial body parts. It was possible that the dinosaur traded larger arms for stronger neck muscles and a more powerful head.
However, we may have been too quick to judge the dinosaur’s arms by the way they look. Paleontologist Steven Stanley argues that those arms may have been more useful than they seemed.
The T. rex had powerful jaws that it may have favored over its arms during its evolution.
Puny arms have made an otherwise fearsome dinosaur look quite comical. The T. rex had a large head, powerful jaws, and an overall intimidating appearance--aside from its arms, that is. The ancestors of the T. rex once had longer arms, but at some point, the dinosaur favored using its jaws or grasping, instead. Thus, the once-longer limbs may have atrophied and shrunk down to about a meter long.
A new study now states that the T. rex may have used its small arms to slash and maim at close quarters. At the end of those seemingly harmless arms were two four-inch-long claws that could cause deep gouges in any prey that the T. rex may have caught
Also, Stanley has found that the bones in the arms were quite strong; they would not be if the limbs had atrophied. The strength of the bones was also able to withstand the force of slashing motions.
“Its short, strong forelimbs and large claws would have permitted T. rex, whether mounted on a victim’s back or grasping it with its jaws, to inflict four gashes a meter [three feet] or more long and several centimeters [more than an inch] deep within a few seconds,” Stanley said. “And it could have repeated this multiple times in rapid succession.”
Did the T. rex even need weapon-like arms?
Stanley also pointed out the presence of an “unusual quasi-ball-and-socket joint” that would have enabled the arms to swing back and forth in several directions and in a slashing motion. Also, tyrannosaurus lost one of its three claws over the course of its evolution. The two claws gave more slashing power, because each one was then able to apply more pressure. The claws were also more like those of a bear’s, which are good for slashing, instead of like those of an eagle’s, which are good for grasping.
However, other scientists aren’t completely convinced yet. “It seems illogical to me to use such small arms to slash with,” said paleobiologist Jakob Vinther. He still thinks that the arms were used for something like grasping or pushing, and needs more evidence to be convinced otherwise. Vertebrate paleontologist Thomas Holtz also pointed out that the arms of the T. rex barely extended past its chest, making its strike zone quite minimal.
Then again, Holtz pointed out, T. rex arms grew more slowly than the rest of its body. Thus, it’s possible that the juvenile members may have been the ones who were able to use their arms for slashing.
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