People have been wondering about the biology of Tyrannosaurus for may years. Some people now believe that Tyrannosaurus was a scavenger.
To be honest when you look at this animal you know that it means business. Others look at the tiny arms and blunt edged teeth and say scavenger. It could not slice flesh or grab prey with its arms, therefore it had to be a scavenger.
It was not that fast, only about 20 miles per hour and the teeth were more adapted for crushing bone than slicing flesh, a feature of a svavenger. The arms were too small. How could Tyrannosaurus possibly kill for a living?
Calculations of Tyrannosaurus's capability as a scavenger within an ecosystem have shown that if it had a reptilian metabolism it could have subsided on scavenged meat for its entire life, but who's to say it was a cold blood?
Whether an animal is warm blooded or cold blooded can affect the amount of energy it needs to live and therefore how much it ate. Cold bloods need less energy because they do not need to produce their own body heat. Something like a mammal however needs extra food to provide enough energy to fuel its internal furnace.
Tyrannosaurus definitely was a warm blooded animal. The hollow bones suggest it. A distant relative of Tyrannosaurus;
Dilong has been found in China with a fossilised coat of feathers. These feathers would only have been used for insulation, useless for a cold blooded animal to absorb heat, but perfect to insulate it.
Tail vertebra of a Hadrosaur (duck billed dinosaur) have been found with neural spine broken and snapped off. The indents in the bone are shaped in an arch formation like a bite. The smoking gun is the shape of the indent, which is identical to the teeth of Tyrannosaurus.
Proof that the Hadrosaur was alive during the attack is the fact that there is healed bone around the broken vertebra. Therefore the Hadrosaur had to have survived the bite for a long time for the bone to have healed to such an extent.
Last is the body proportions. Tyrannosaurus, although slow and heavy as an adult, was fast and long legged as a juvenile. Recently discovered bone beds show groups of Tyrannosaurus of all ages that died together at the same time. This suggests pack hunting or grouping behaviour.
Perhaps the longer legged juveniles chased the prey into an ambush like female lions today. The larger adults then attack the exhausted prey, using their huge jaws full of teeth not to slice meat, but grip and crush the prey, killing it instantly.
The arms were small because Tyrannosaurus didn't need them. When you have a head the size of a small car you can just crunch your victims to death. This is unlike other predatory dinosaurs that used their arms to grab prey and tear it up.
The fact is, Tyrannosaurus was probably both a scavenger and a predator. Most lions will happily scavenge from a carcass of an already dead animal. Hyenas will happily attack a wildebeest if weakened or alone. Since Tyrannosaurus was the only large meat eater (with exception of Raptors which used large numbers to bring down the largest of prey animals) in its ecosystem we can safely assume that it had to have occupied niche of top carnivore once in a while.
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