Predator or Scavenger?  The Tyrannosaurus rex debate.

By Stefanie Seeger

Tyrannosaurus rex, the mighty hunter, has come under attack by Horner (1994). He believes that T. rex has been mislabeled as a predator and is actually a scavenger.  A brain cast was made from a T. rex skull and Horner found that the optic nerve was very small and the olfactory cavity was large and comparable in proportion in size to that of a vulture.  This led Horner to believe that T. rex had poor eyesight but with an amazing sense of smell, T. .rex would have been able to smell carrion miles away.  Running is also out of the question for T. rex, as reported by Hutchinson (2002). Fast bipedal animals have short thighbones and long shinbones and they don’t require more than 5% of their body weight in each leg.  T. rex has longer thighbones and the ability to run would require 7-10% of its weight in each leg, providing a maximum speed of about 25 mph. 

            Evidence for scavenging is common in the literature; however, there is new evidence that shows that T. rex had the ability to hunt. Erickson (1996) found that T. rex’s teeth were strong enough to handle struggling prey while delivering bone-crunching power.  A Triceratops pelvis was found exhibiting T.rex bite marks.  Using a cow bone and aluminum and bronze T. rex teeth, Erickson wanted to find out how much force was necessary to reproduce such bite marks.  The back teeth had the most leverage and had a bite force of 13,400 N, the strongest bite force of any known animal.  The American alligator is not far behind with 12,000 N. (Fig. 1). Direct evidence of T. rex hunting was found on an adult Edmontasaurus, which had escaped the T. rex and had healed bite marks in its tail.  Although Horner believes that T. rex was strictly a scavenger, there are scientists with the view that as modern predators will eat carrion; scavengers such as vultures will also kill. T. rex may have behaved similarly, as an opportunist, which didn’t turn down a free meal but also wasn’t scared to hunt down its own.

Figure 1.  Bite force estimation of Tyrannosaurus rex and other modern day animals.  Scientific American, Sep 1999, Vol. 281 Issue 3

References:

Dinodata.  2000, http://www.dinodata.net/

Erikson, Gregory M. 1990.  Breathing Life into Tyrannosaurus Rex.  Scientific American 281.

Erikson, Gregory M., Van Kirk, S., Su, J., Levenston, M., Caler, W., Carter, D. 1996.  Bite-force Estimation for Tyrannosaurus rex from tooth-marked bones. Nature 382, 706-707.

Fitzgerald, Richard. 2002. How Fast Could Tyrannosaurus rex Run?  Physics Today 55.

Horner, John 1994.  Steak Knives, Beady Eyes, and Tiny Little Arms.  The Paleontological Society Special Publication No. 7.

Hutchinson, J., Garcia, M.  2002.  Tyrannosaurus was not a fast runner.  Nature 415 1018-1021.

Locke, Robert.  2001.  Killing a Legend.  Dinosaur Magazine, Circa Media. El Paso, Texas.

Museum of the Rockies. 2003, http://museum.montana.edu

Tyrannosaurus Rex.  2003, http://www.enchantedlearning.com/subjects/dinosaurs/dinos/trex/index.shtml