T-Rex guards his dinner. (Copyright
Lee Krystek 2003)
He's 40 feet long, 18 feet high, weighs six tons
and has a four-foot-long mouth filled with sharp teeth seven inches
long. What's more, he can chase his prey across an open plain
at speeds of forty miles per hour and when he catches his victim,
one bite from his massive jaws can break their backbones. His
name means tyrant lizard king and he is the most feared
predator that ever lived: Tyrannosaurus Rex.
Despite his impressive height, weight and length,
some scientists, including paleontologist Jack Horner, think that
the T-Rex, a huge, therapod dinosaur
from the Cretaceous period, didn't chase down its prey at all,
but was merely a scavenger. As a scavenger he fed off of already
dead animals, killed by old age, disease, or other carnivores,
to get his meals. Dr. Horner points out that some of today's largest
birds, like the vulture, are scavengers (Birds are thought to
be the dinosaurs' closest living relatives). Proponents of the
scavenger theory also note that the T-Rex's scrawny front arms
seem inadequate to hold a victim during an attack (Others point
out some creatures, like the great white shark, are successful
predators even with no arms at all). Horner also thinks T-Rex's
legs were optimized for walking, rather than running prey to ground.
He probably followed a large herd of animals, like Triceratops,
waiting for one of them to keel over. Fossil examination show
that the T-Rex's olfactory lobes (the part of the brain that handles
smell) were huge. On one fossil specimens they were found to be
as large as grapefruits. These huge lobes suggest that a Tyrannosaurus
might be able to smell a rotting carcass, his next meal, from
T-Rex meets an old enemy: A Triceratops that does not want
to be dinner. (Copyright Lee Krystek,
Also, the Tyrannosaurus' height and size might have
been more useful for seeing long distances to find his meals and
chasing off other dinosaurs competing
for a carcass rather than for hunting live prey.
Other scientists argue that scavenging for food
and hunting aren't mutually exclusive activities and T-Rex might
have done both depending on what was easiest. Such is the case
with lions in modern Africa. They hunt when they have to, but
are happy to steal a carcass from a smaller predator, like the
hyena, when they can.
One thing for certain about Tyrannosaurus is that
they fought fiercely among themselves. Several Tyrannosaurus skeletons
have been found with wounds made during attacks by other T-Rex's.
It is clear that since some of the wounds had healed they weren't
the result of scavenging after death. The clashes were probaby
over food or territory. With the strength a T-Rex has in his jaws,
the loser must have walked away in considerable pain.
According to Gregory Erickson, T-Rex had an incredibly
powerful bite. Erickson, a researcher with University of California
at Berkeley, reproduced the results of a Tyrannosaurus bite by
using a bronze-aluminum cast of a tooth in a hydraulic press.
By comparing the damage the fake tooth did to a cow pelvic bone
with a fossil Triceratops bone that had T-Rex marks, Erickson
estimated that the Tyrannosaurus was able to bite with a force
of 3,000 pounds. That's the equivalent of a pickup truck sitting
on top of each tooth. Erickson thinks T-Rex was capable of even
a much stronger bites during an attack. The marks on the Triceratops
were only a "feeding bite," not meant to kill.
You Don't Move...
In the film Jurassic
Park, paleontologist Dr. Alan Grant and a young girl
are cornered by a T-Rex. "Don't move," he tells
her. "If we don't move he won't see us..."
If this true?
Was a Tyrannosaurus's vision based on motion?
It made for a
dramatic escape from death in the movie, but there's no
real evidence that the T-Rex had this weakness in reality.
that T-Rex's vision was quite good and there is no reason
to think it could only see moving objects. Even if the T-Rex's
vision was so bad it needed glasses, however, it was quite
capable of tracking down its prey based solely on smell.
If that scene in Jurassic Park had been for real,
it would probably have had a much sadder ending.
Two other researchers, James Farlow and John Robinson,
have made some calculations about T-Rex's speed that may support
Horner's scavenging theory. According to Farlow and Robinson,
if a full-sized T-Rex running at 40 miles per hour tripped, the
result would be catastrophic. Weighing as much as he did, the
dinosaur would hit the ground with tremendous force probably cracking
his skull, squashing his internal organs and finally, at the end
of a fifty foot skid, breaking his neck.
Even at a more conservative 25 miles per hour, which
Farlow and Robinson think was really the T-Rex's upper limit,
the damage would still be considerable. They estimate T-Rex rarely
went more than fifteen miles per hour because of the danger of
If they are right, their ideas tend to support Horner's
scavenger theory. At fifteen miles per hour, T-Rex might find
it hard to keep up with smaller and faster dinosaurs that might
make a good lunch.
Bad, But Maybe Not the Biggest
T-Rex may even find his claim to being the largest
meat-eating dinosaur in question. Paul Sereno, a paleontologist
from the University of Chicago, has unearthed a giant 50 foot
long predator that lived 90 million years ago in what is now Africa.
Carcharodontosaurus saharicus, which means
"shark-toothed reptile of the Sahara", had been named for many
years. Little was known about it, however, as the single specimen
found was destroyed while it was being studied in Germany during
World War II. Sereno's beast, dug out of the ground in the Moroccan
Sahara, appears to be larger than any known specimen of Tyrannosaurus
Rex ever found.
might be one of several dinosaur predators larger than T-Rex.
Another rival for the largest dinosaur carnivore
is Spinosaurus. Paleontologists think this giant, whose
fossils have been found in northern Africa, was as long as fifty-nine
feet and weighed 9 tons. The most spectacular feature of Spinosaurus
just wasn't his great size, however, but a six-foot tall "sail"
or hump that ran along his back. Spinosaurus was featured
in the movie, "Jurassic Park III," where it fought and
killed a T-Rex. Though speculating about such a battle is fun,
it would not have happened. Though Spinasaurus and T-Rex both
lived during the late Cretaceous Era they were still separated
by over twenty million years in time. They also lived on two different
continents. Spinosaurus is currently thought to be the
biggest dinosaur predator that ever lived.
Another dinosaur bigger than T-rex was Giganotosaurus.
Giganotosaurus lived in South America during the Cretaceous era
and was one of the biggest land-dwelling meat eaters to ever walk
the face of the earth. Giganotosaurus, whose name means "Giant
southern lizard," grew as long as 43 feet and weighed between
6.5 and 13.3 tons. Though Giganotosaurus seems to have filled
the same niche in the South American eco-system as Tyrannosaurus
in North America, paleontologists think that they were in no way
"The Humongous Book of Dinosaurs."
More about T-Rex from UC at Berkeley
The Ultimate Dinosaurs, Edited by Katie
Orchard, Parragon Books, 2000.
Dinosaur Heresies, by Robert T. Bakker,
Ph.D., William Morrow and Company, 1986.
The Complete T-Rex, by John R. Horner and
Don Lesson, Simon & Schuster, 1993.
Copyright Lee Krystek
1996-2003. All Rights Reserved.