Tyrannosaurus Rex, was it a “vicious” Hunter that attacked others or a “lowly” scavenger that ate the scraps from true predators? This has been debated ever since the first skeletons were uncovered, at least for several decades. The topic was immortalized in the comic strip series Calvin and Hobbes (Bill Watterson) in the early 1990’s when Calvin chose it as a subject for his school paper. As Calvin so succinctly put it, after having his brain enhanced, “It requires a brief overview of carnosaur evolution…delving into skeletal structure, skull design, arm strength, potential running speed and environmental factors”. Unfortunately Calvin’s brain shrank back to normal and he proceeded to draw sketches of T-rex eating people in the Museum of Natural History. But Calvin’s thesis and comments are a good starting point.
The skeleton of T-rex shows that it was a massive animal with a skull full of grooved, razor sharp teeth. The eyes were relatively small but were set in the skull looking forward so it should of had stereoscopic vision and it appears to have possessed large olfactory nerves for a good sense of smell. Fossil records show short forearms and powerful hind legs with a long tail for balance, indicating to most experts that it could possibly run at reasonably high speeds. Does this indicate hunter or predator, or maybe even both?
The size to most would indicate a predator as they are usually larger than scavengers, but the prey in this case was huge dinosaurs and size is relative. Both hunters and scavengers had grooved, sharp teeth needed for killing and/or ripping open carcases, crushing bones. The small eyes with an enhance sense of smell is usually associated with scavengers, but the ability to judge distance and speed given by the stereoscopic vision are indicative of pedators; scavengers rely on side vision to watch out for hunters as the dead remains don’t move. The short forearms were considered weak and useless for hunting, but most animals don’t use their forearms for killing and scavengers rarely have powerful hind legs that are built for speed.
There have also been fossilized skeletons of other dinosaurs found with healed bones showing characteristic scars from tyrannosaurs. This would indicate prey escaping from a hunter, or would it? It could indicate something else such as an animal protecting its territory or nest; chickens will attack a dog to protect their nest, but they are not hunters or scavengers!
T-rex was thought to be solitary (but this is guessing), which indicates a hunter. Hawks hunt by themselves and yet vultures travel in flocks. This is mentioned as many palaeontologists believe the dinosaurs became birds, so bird behavior can possibly help us estimate dinosaur behavior.
And estimating or theorizing is all that can be done! So after having delved “into skeletal structure, skull design, arm strength, potential running speed and environmental factors” as Calvin told us was essential, we still don’t know. The evidence can be read both ways, hunter and scavenger. Why not both, it would explain a lot! Lions, tigers and wolves all kill their own prey and scavenge from others when the chance arises, may be tyrannosaurs did as well.
Though many people, like Calvin, would prefer to say “Tyrannosaurs were predators, because it would be so bogus if they just ate things that were already dead”, it was likely both ways.