Carnotaurus, a wimpy-armed meat-eating dinosaur had a huge tail muscle that that a researcher said made it a speedster and one of the fastest running hunters of its time. 

The seven-meter long dinosaur predator that would trouble its plant-eating neighbours in South America was much deadlier than first thought, a University of Alberta paleontology graduate student Scott Persons said.

Upon closely examining the tail bones of Carnotaurus, the researcher found that its caudofemoralis muscle had a tendon attaching to its upper leg bones. When this muscle was flexed, it pulled the legs backwards and gave Carnotaurus ample power and speed in every step it took.

Persons found a similar tail-muscle and leg-power combination in early research in another predator, the Tyrannosaurus rex. Many dinosaur researchers thought T. rex's huge tail just served as a counterweight to its massive head.

However, Persons' examination of the tail of Carnotaurus showed that along its length there were pairs of tall rib-like bones that interlocked with the next pair in line.

By using 3-D computer models, Persons recreated the tail muscles of Carnotaurus and found that the unusual tail ribs supported a huge caudofemoralis muscle.

The interlocked bone structure along the dinosaur's tail did cause one drawback though: the tail was rigid and this made it difficult for the dinosaur hunter to make quick, fluid turns.

Persons said what Carnotaurus gave up in maneuverability, it certainly made up for it in straight ahead speed.

Carnotaurus had the largest caudofemoralis muscle of any known animal, living or extinct, for its size, according to the study published in PLoS ONE on Oct.14.