Kingdom Animalia 
Phylum Chordata
Class Archosauria
Order Saurischia
Suborder Theropoda
Infraorder Coelurosauria
Superfamily Maniraptoriformes
Family Tyrannosauroidea 
Genus Tyrannosaurus 
T. rex was a huge carnivore that lived during the late Cretaceous period, about 85 million to 65 million years ago. Until recently, it was the biggest known carnivorous dinosaur. Tyrannosaurus rex was a fierce predator. They walked on two powerful legs and had a huge head with large teeth and well-developed jaw muscles. It had tiny arms with two fingers each. They had three large toes, all equipped with claws. They had a slim, stiff tail that provided balance and allowed quick turns. They were up to 40 feet and weighed 5 to 7 tons. Tyrannosaurus rex probably lived in forests, where they could find plenty of food. They could see and smell well. T. rex was a fairly smart dinosaur. They appear to only have cared for their young for a very short time. They appear to have been solitary dinosaurs. Their favorite food source was the Triceratops.

The largest, best-preserved, and complete T rex is named Sue, after Sue Hendrickson, the woman who unearthed it from western South Dakota on August 20, 1990. 67 million years back, Sue (the lizard, not the fossil hunter) crushed small creatures with the weight of seven tons. Her skull alone weighs 750 pounds (at 5.2 ft. long). Sue had serrated teeth up to a foot long and was 42 feet snout-to-tail. Most of her 250+ bones have been found. If you live in hardcore Chicago, you may ogle Sue beginning May 17th, at the Field Museum of Natural History.

As figured by dinosaur artist and scientist Gregory Paul in his now out-of-print text Predatory Dinosaurs of the World, an adult T. rex had the capacity to take a bite out its prey one yard long by one foot deep. The ability to scoop such a trough from the side or flank of a prey animal lends support to the theory that T. rex hunted in a fashion similar to that of a great white shark, i.e. by creating a massive wound in one strike and then trailing far behind the prey until it bled to death, thereby avoiding a nasty entanglement with the prey's horns, armor, claws, etc. This would be important, as theropod bodies in general were fairly rigid and relatively lightly built, not well-suited to taking a spill from their normal bipedal posture.

T. rex was discovered and named by paleontologist Barnum Brown, who actually named it twice.

The first skeleton Brown excavated, he named "Dynamosaurus imperiosus." On the same expedition, he found another, more complete specimen, which he interpreted as another genus and species: Tyrannosaurus rex.

Later on, Brown realized the error in his classification. The differences between the two specimens were just the inevitable result of spending 70 million years under tons and tons of rock.

One would think that Brown would go with the name of the type specimen, Dynamosaurus. However, in the initial scientific paper he wrote on the two animals, classifying them separately, Tyrannosaurus was mentioned first. Since T. rex was classified first, that was the name Brown went with. Such are the eccentricities of biological nomenclature.

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