T Rex used its tiny arms for vicious slashing: study

The fearsome T Rex dinosaur used its small arms to viciously slash its prey, according to scientists who showed that the prehistoric carnivore's front limbs were far from useless.
For more than a century, many paleontologists have viewed the small arms of T rex as having been vestigial.
At about a metre long, these arms were not as tiny as often portrayed, and its traits indicate that they were actually functional, researchers said.
Scientists from the University of Hawaii in the US showed that the arms' were adapted for slashing preys at close quarters.
The shortness of the arms would actually have been advantageous for this activity, they said.

According to the research, the arms were very strong. They were slightly longer than the leg of a six-foot man, with similar girth.

The arm bones were quite robust and would readily have sustained the impact of slashing, researchers said.
"The unusual reduction of the number of fingers from three to two would have resulted in 50 per cent more pressure being applied to each claw," they said.
An unusual quasi-ball-and-socket joint that would have allowed considerable mobility for slashing. The 8-10 centimetre long, sickle-shaped claws would have caused deep wounds.
The 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 or more long and several centimeters deep within a few seconds - and it could have repeated this multiple times in rapid succession.

Tyrannosaur ancestors used long arms primarily for grasping. These atrophied during the evolution that led to the tyrannosaurids because the jaws took over their grasping function.
The expansion of the head deprived the arms of nutrition. As the arms approached their final size, natural selection kicked in and put them to good use for slashing at close quarters, researchers said.