As ferocious as Tyrannosaurus rex was, its useless little arms have made it the butt of some excellent jokes. Now researchers are saying that tyrannosaurids never needed proper arms anyway, since their necks were such powerful instruments for wielding their killer jaws.
To reconstruct T. rex neck function, a team led by Eric Snively from the University of Wisconsin–La Crosse looked to raptors (the modern bird kind), documenting their feeding behavior and recording the electrical activity of their muscles. Video of these extant raptors reveals the involvement of the neck when striking at prey and tearing flesh. Since tyrannosaurids had most of the same muscles, the researchers reasoned, there’s a strong possibility that they behaved in the same way.
The team placed electrodes on the skin of a dozen birds from 10 different species, ranging from chickens to bald eagles. This allowed them to identify the precise muscle movements that underlie each stage of feeding. The team was particularly interested in the avian muscle M. complexus, which is used for head dorsiflexion (upwards flex) and lateroflexion (to the side).
They found that the birds raised their heads and fixed their gaze on their prey before lowering their heads to attack. Since T. rex had many of the same muscles, the work suggests how the dinosaur could perform the same movements: raising its head and thrusting it upwards. The muscle also helped stabilize the head as T. rex tore flesh by rearing back its body through the extension of its legs.
Additionally, many of the birds also shook their necks -- like a dog shaking off water. Snively thinks that the dinosaur used this motion to dislodge meat from a carcass. According to one reconstruction, the tyrannosaurid neck muscles combined the functional regionalization seen in birds, with the robustness of crocodilian musculature. "We can think of them as striking like a bird, and shake-feeding like a crocodile," Snively tells New Scientist.
Well that explains it. "Tyrannosaurs didn't need big arms to hunt, because their powerful bites and hyper-bulldog necks did the job," Snively explains. "From the shoulders forward, T. rex was like a whole killer whale: just bite, shake and twist." So many wonderful animal metaphors.
The work was published in Journal of Zoology this month.
[Via New Scientist]
Image: J. Fang
