Talk about a triple threat. If you thought tyrannosaurs weren't scary enough, try three of them at the same time. Turns out these fearsome beasts weren’t solitary hunters — they ran in gangs, said a study of the first fossil tyrannosaurid trackways ever discovered.
The three sets of fossil footprints, described in a PLOS One paper called “A Terror of Tyrannosaurs,” show clear evidence that these animals were “gregarious”: They operated in packs rather than alone, as once thought.
Tyrannosaur footprints have been few and far between, said the study led by Richard McCrea, a researcher at Peace Region Palaeontology Research Center. A series of footprints (referred to as “trackways”) can reveal things that bones alone may not, including the animal's gait, how fast it could go and who it was traveling with at the time.
But in October 2011, Aaron Fredlund, a local guide-outfitter, stumbled upon the animal’s trackway in British Columbia. The footprints, which stretch longer than 19.5 inches, are all pointed in the same direction, and are within 8.5 meters of each other. Since these large predators were typically few and far between on the landscape — “only five percent of the faunal composition,” the authors write — it’s highly unlikely that three tyrannosaurs just happened to be in the same place at the same time walking in parallel. By analyzing the gait of each animal from one footprint to the next, the scientists think the animals were traveling around 3.9 to 5.3 mph.
Los Angeles Times