T rex an bait eater

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 sustainence - 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 a reason - 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 cushion itself.

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 doesn't 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 tibia compared the femur. T rex couldn't eat what it couldn't 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. Calculations 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 doesn't 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 possesses well-developed binocular vision. Unlike its South American contemporaries such as Giganotosaurus, T rex had depth perception. This wonderful innovation is designed specifically for focusing on and stalking prey.

Another strong piece of evidence for predatory activity comes from track ways. Track ways 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 pursuing 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 didn't 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 track ways 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 ferocious life. The physique of T rex tells us that it was a strong, quick animal with a hunter's eyesight and a powerful jaw for a weapon - a jaw for killing other giant dinosaurs.