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T. rex
has been assumed to be an active hunter since it was first discovered
in 1905. Jack Horner has recently been challenging this assumption.
He goes further than to suggest this animal might have scavenged,
he says that this animals was never - and could never - have
been an active hunter.
I
believe that the various pieces of evidence put forward to indicate T. rex was
"100% scavenger" aren't conclusive. Furthermore I believe that evidence
can be found to show predatory behaviour. Do
puny arms indicate an inability to hunt? Jack
Horner suggests that useless little front limbs are a strong indication that T
rex scavenged. They cannot be use to prevent a dangerous tumble while hunting,
nor can they be used to kill. He says that small, agile animals are the best predators
because they have big arms with fingers and dexterous claws. Few
active predators today use forelimbs in hunting or killing. Birds of prey are
the modern-day relatives of dinosaurs and they are superb hunters using only feet
and beak. Crocodiles are the closest animal we know which can show the raw reptilian
bite force that T rex must have been able to exert. Their jaw is their only weapon.
Therefore T rex's small arms cannot rule out predatory behavior. I
believe that the tiny arms are actually the strongest reason to believe that T
rex must have evolved as an active hunter. A scavenger in a food chain does not
need to be big in order to survive. A good scavenger is small enough to rely on
scraps for food. T rex on the other hand evolved to be the largest meat-eater
ever in North America. Being big is a disadvantage if you're relying on other
people's leftovers for sustainance - but its a great advantage is you're a hungry
killer. The
primary weapon of T rex - or any hunter - is its mouth. Therefore the arms are
reduced in size for areason - to maintain balance to allow the evolution of one
of the largest jaws ever known. The larger and more powerful an animal's bite,
the more deadly it is. A scavenger would not need such devastating force to pick
rotten meat from dead bones. The
arms have not been completely evolved away so they must have served a purpose.
They are in a prime position to heave the animal off the ground from a resting
position. This is probably necessary on a day-to-day basis but the extra lift
might have been very useful when ambushing prey. Would
fear of injury stop T rex from hunting? Horner
says that predatory animals must fight and jump and therefore might fall. If T
rex fell it might break its jaw and ribs and could not recover, particularly without
strong arms to cusion itsself. Take
other animals for instance - A fall can be fatal to a giraffe and yet they frequently
run. Monkeys die falling from trees but it doesnt mean they stop climbing. There
are many examples of how everyday life can be a potential death-trap. The
fossils record bears witness to the rough and dangerous life of large, theropod
dinosaurs. The most famous and most complete T rex skeleton, Sue, has a broken
fibula. Injury
in herbivorous dinosaurs is comparatively rare, however one quarter of all theropod
dinosaur skeletons show a fracture in an arm or leg. One
of the best-known theropods is an Allosaur specimen named "Big Al".
This animal suffered the following injuries during its life: - Fractured
left lower leg bone
- Infected
right foot bone
- Fractured
tail
- Fractured abdominal
ribs
- Fractured right
rib
- Damaged claw sheath
on the second finger of left hand
- Infected
and fractured second and third fingers on the right hand
- The
second finger of right hand twisted
- Fractured
second finger on left hand
- Partial
fracture in one right rib
- Infection
in right shoulder
- Damage
to left pelvic bone, a re-healed fracture.
I
am prepared to believe that some of the injuries could have been sustained during
fights with rivals, however the injury to the right foot is very similar to those
seen in running birds like ostriches when they trip. Falling
would have been one of many hazards in the dinosaur world. A
final point: Hunting can even be performed very effectively without running -
Crocodiles are a prime example of the ambush predator. They have a muscle in the
tail which they use to launch themselves forwards with great power. T rex has
very similar muscle in its tail. Perhaps the tail, - along with the small but
very powerful arms - would launch the T rex from a secluded hiding place towards
its unwitting prey. Did a lack
of speed stop it hunting? By
looking at the proportions of T rex legs Jack Horner shows that T rex was not
a runner. It has a short fibia compared the femur. T rex couldnt eat what it couldnt
catch. This
observation must be placed in context. The prey of T rex would have been other
large animals. T rex only needed to be as fast as the animals upon which it fed,
such as Edmontosaurus or Triceratops. Caculations have shown that, even without
running, a 12m long T rex would easily reach 25 miles per hour. At good stride
T rex could certainly match a Hadrosaur and possibly Triceratops. Also,
as outlined above, an ambush predator would not need speed. Does
a T rex brain show it to be a scavenger? C.A.T.
scans of T rex skulls show us the brain case and therefore, roughly, the shape
of the brain. Jack Horner explains that Tyrannosaurs had a large olfactory lobe
and a small optical system. He points out this is very similar in proportion to
a vulture. Vultures use their keen sense of smell to scent dead meat over tens
of miles and, if T rex had the same type of brain, then it too must have been
a scavenger. The
brain of T rex was also very similar to another modern-day animal: The Alligator.
Birds (including vultures) have an enlarged area of the brain devoted to processing
data however alligators, like large theropod dinosaurs, have a smaller part of
the brain developed to processing and a large portion devoted to just receiving
sensory input. This doesnt tells us if the food was been sought out living or
dead, but rather how the hunter reacts when it reaches it. With
a lot of processing power in the brain, a bird can effortlessly pick out morsels
of food from amongst the general debris lying on the ground, finding objects as
tiny berries. Alligators are opportunistic eaters and they will go for anything
they perceive as a food item. Theropods' brains show that they had the same hunting
instinct as an Alligator. T
rex may have had an incredibly well-honed olfactory sense like a vulture - just
as Horner suggests - but once it reached its prey it probably fed just like an
alligator - with a powerful, devastating jaw attacking a live animal. Is
there no evidence to show predation? Jack
Horner insists that all the evidence so far shows 100% scavenger and there is
no evidence to show it was a predator. Horner uses the rex-bitten sacrum of a
Triceratops as evidence that the carcass was scavenged by T rex. The sacrum is
not a very accessible part of an animal so he concludes it has been eaten by T
rex long after other animals have eaten all the choicer morsels. This
proves nothing except that T rex bit that part of the animal at some point, be
it before or after the kill. More importantly if T rex did not kill the Triceratops
then there is no other animal around at the time which could. This is to suggest
that all of T rex's diet came from animals that died of natural causes or an accident.
Evidence exists to show Tyrannosaurus lived in packs and it therefore seems implausible
to believe that enough herbivores would drop dead of illness to support large
groups of rexes. Horner
insists that study of the skeleton alone shows it to be all scavenger. There is
one very important feature which is not mentioned. T rex posesses well-developed
binocular vision. Unlike its South American contemporaries such as Giganotosaurus,
T rex had depth perception. This wonderful innovation is designed specifically
for focussing on and stalking prey. Another
strong piece of evidence for predatory activity comes from trackways. Trackways
exists that show a theropod dinosaur stalking a sauropod. The theropod matches
the movement of the herbivore, clearly following it. There is no logical reason
why a scavenging animal would follow a live herbivore unless it somehow knew its
life was about to end. The more explanation is that the persuing animal was plotting
the demise of the other by foul play. No
Hunters in the Eco-System? Removing
large theropods from the top of the food chain leaves a vacuum. Without a top
predator there is nothing to control the population of the large herbivorous animals.
This model doesnt occur in nature.
Furthermore, if large herbivores in the late cretaceous were not prone to attack
from large, active predators then why would Ankylosaurus develop the thickest,
most sophisticated body armour ever known? Why would Triceratops have such a large
defensive frill and massive, offensive horns? Saltasaurus
was a large sauropod that had body armour embedded in its skin. Although it didnt
live in the same region as T rex, a similar titanosaur called Alamosaurus did.
These animals were at no risk from any small predator so what would have been
the need to evolve body armour if the likes of T rex were scavengers? Conclusion The
evidence, when examined in context, shows that T rex and other large theropods
had all the attributes to be active predators. The
fossil record shows trackways of large theropods stalking live animals.
Reconstructions of the skull show that T rex had a brain like an alligator, one
of the deadliest animals alive today. Tyrannosaurus skeletons bare the numerous
broken bones which were sustained during their fast and ferocous life. The physique
of T rex tells us that it was a strong, quick animal with a hunter's eyesight
and a powerul jaw for a weapon - a jaw for killing other giant dinosaurs. ©
2001-2006 Gavin Rymill |