T-REX, a Predator or a Scavenger?
Could Jurassic Park ever really happen? How much of what you saw in Jurassic Park can be considered real? Discuss all of that and more here...

17 May 2005, 03:51

Okay, this one links to the DEBATE POST...
Read the Post titled: "Is the T-Rex a hunter or a scavenger?"
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the extinct
 
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05 Jun 2005, 18:03

Okay first of all, there is no such thing as a definate scavenger. Hyeanas dont scavenge much, Vulchers often hunt lizards, and the list goes on and on. Plus, these are all small animals, with relativly small amounts of food needed.
Now, consider the tyrannosaur. Very large, warmblooded, active animal. Big leg muscles, big head, bone crushing bite. Several Biomechanical observations (read Bakker, Paul, etc.) show that this animal would have died if it took up the exclusive scavenger role.

One thing I dont get: Horner thinks dinosaurs are warm blooded, right? Well, he is being a hypocrite. His T.rex, as he shows it, is a "cold blooded" swamp monster, un able to hunt. But to cover the distances needed to find enough food, it would have to have a slow metabolism to survive the wait. But to get there before bying the farm, it would have to be as fast as a warm blood.

I am not denying that a Tyrannosaur, upon coming upon an edmontosaur carcass, would partake. But the difficaulty of being an exclusivly, or mostly, carrion eating animal is far greater than just hunting and getting fresh meat.
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an egg
 
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11 Jun 2005, 20:07

TREX-- SCAVENGER OR PREDATOR...?





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 sufferend 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 Gavin Rymill
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the extinct
 
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12 Jun 2005, 22:29

*gives standing ovation to Nissin* THat's right, you tell them.
When all is said and done and the world is empty how much does it really matter the amount of money you had or what car you drove?
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db 2nd generation
 
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13 Jun 2005, 00:08

lol...
hmmmm, I'm not sure if THAT was a compliement Tyrannis...
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the extinct
 
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13 Jun 2005, 14:55

sure it is.
When all is said and done and the world is empty how much does it really matter the amount of money you had or what car you drove?
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14 Jun 2005, 02:30

Ok, if you say so...
lol
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the extinct
 
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17 Jun 2005, 14:15

I would definatly say that T. rex was a hunter. But I think it would scavange whenever it could if it didnt want to hunt or anything like that.
But well I actually think that it was both, but mostly hunter.
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a hatchling
 
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17 Jun 2005, 23:49

Its just that...
as children, we are bought up with the media showing us that T-rex is a hunter. For example-- In " J.P" and in "The Land Before Time"...
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the extinct
 
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20 Jun 2005, 17:09

That's exactly the point i make first when i'm often confronted with this debate, because i too was raised with the images of the Jurassic Park T-Rex(thus becoming my favorite dinosaur before i gave that up to favor them all equally)We are influenced to believe that THAT is definite FACT, and as we mature, we tend to have a hard time accepting it in any other way. However, it is still entirely plausible the other way. When I first heard Horner's theories, i started to second guess it(it took me a while before i started though) but after hearing his theory and reading yours in here, i have to say that i was blind to think that it HAD to be more one than the other, or just one exclusively. I thank you for opening my eyes on that. I think it is most probable that is was both predator and scavenger, maybe switching between the two depending on the situation, and health status. It would not be mostly of either one.
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