sentences:  The near-absence of herbivore remains and the similar state of preservation common to the many individuals at the "Albertosaurus" bonebed quarry led Currie to conclude that the locality was not a predator trap like the La Brea Tar Pits in California, and that all of the preserved animals died at the same time.Currie claims this as evidence of pack behaviour.Other scientists are skeptical, observing that the animals may have been driven together by drought, flood or for other reasons.