No Longer A Loner

Evidence from other dinosaur finds have provided additional clues to T. rex's modes of behavior. Paleontologist Robert Bakker of the Tate Museum in Casper, Wyoming, reported in 1998 on the excavation of a nest belonging to an Allosaurus, a theropod ancestor of T. rex that lived in the Late Jurassic and Early Cretaceous periods. Bakker found the remains of prey at the nest, evidence that the parents brought food to their young. Bakker argued that as ferocious as the Allosaurus and T. rex undoubtedly were, they may have lived in families, rather than as lone hunters, and cared for their young.

Peter Larson's excavations in South Dakota have supported that theory. At the site where Larson's team discovered Sue, they also found other T. rex individuals, including another adult and two juveniles, that may have been part of a group.

Paleontologist Philip Currie of the Royal Tyrrell Museum in Drumheller, Canada, has developed theories about tyrannosaurid group behavior based on investigations of the Albertosaurus, a Cretaceous dinosaur that was similar to T. rex. In 1997 in the Canadian province of Alberta (from which Albertosaurus gets its name), Currie rediscovered a site with numerous dinosaur fossils that Barnum Brown had begun to excavate in 1910. Currie found the fossils of 10 albertosaurs, ranging from juveniles about 5 meters (16 feet) long to adults about 10 meters (33 feet) long. Currie concluded that the Albertosaurus--and other tyrannosaurids--lived in groups and hunted together in packs. He argued that the younger, leaner juveniles would have been swifter than the full-grown adults and therefore useful in “rounding up” potential victims.

In 1999, Bakker excavated the first nearly complete juvenile T. rex skeleton, a discovery that added weight to the idea that the younger animals were fierce predators in their own right. The juvenile T. rex, nicknamed Tinker, had teeth about the same size of those in a full-grown adult. On the other hand, though Tinker was about two-thirds the length of an adult when it died, its bones were relatively slender, suggesting that the young dinosaur was only about one-fifth the weight of a full-grown T. rex. Thus, Tinker must have been a lean, fast, and deadly predator--a perfect member of a pack of T. rex hunters.

Other evidence of tyrannosaurid cooperation includes indirect evidence of caring for the injured. Larson noted that Sue had a broken leg bone, which had healed but must have incapacitated the dinosaur for some time. Larson suggested that the T. rex could only have survived with the help of other individuals who brought it food while the leg healed.

Images of group cooperation, family life, and nesting habits are a far cry from the first descriptions of T. rex in the early 1900's and the long-held assumptions about the tyrant king as a solitary hunter. The traditional portrayals of T. rex in films and novels can make it difficult to imagine this terrifying beast in any other way. And as the towering skeleton of Sue demonstrated at the opening of the Field Museum exhibit in 2000, T. rex will always arouse a sense of amazement at the animal's deadly fierceness--apparent even in bare bones. Nonetheless, our evolving understanding of the Tyrannosaurus as a social creature as well as a deadly predator make it seem even more lifelike.