Perhaps the second most famous carnosaur after Tyrannosaurus Rex, Allosaurus lived about 155 million years ago during the Jurassic Period. It was named using the Greek words “allos”, which meant different, and “saurus” which meant lizard. Therefore, its name literally means “different lizard”. It was given this name because its skeleton was quite different than any other dinosaur found up until the time of its discovery. The most of the specimens of this dinosaur have been found in Colorado, Montana, New Mexico, Africa, Australia. Tanzania and parts of Europe. Allosaurus was a large carnivorous, it had rows of razor sharp teeth that had saw-like formations on its edges. It is believed that the Allosaurus was able to attack larger predators with these teeth by using its upper jaw like a hatchet and attacking using the element of surprise. Allosaurus had a short neck and a narrow, elongated skull, which was disproportionately large, similar to those of other big carnivorous theropods. But unlike other theropods, it had a pair of small horns above its eyes, which were extensions of the lacrimal bones in the skull. It also had ridges that ran along the top of the nasal bones to the horns. Allosaurus' massive body was supported by two powerful hind limbs and a large tail. Each foot had three weight-bearing toes and an inner dewclaw. Models suggest Allosaurus could run up to 21 mph (33.8 kph). The size of the largest Allosaurus is approximately 16 feet tall, 43 feet long and weighed more up to 5 tons. This contrasts pretty well with the T- Rex who was approximately 13-16 feet tall, 42 feet long and weighed approximately 7 tons. The Allosaurus is an extremely aggressive and dangerous predator, even more so when accompanied by its ever-present pack mates. Approach with caution - you may not always have visual on its nearby allies when approaching a singular Allosaur. It was capable of killing healthy medium-sized sauropods (long-necked herbivores) or large sauropods, such as Apatosaurus, that were sick or injured. Allosaurus was among the earliest dinosaur discoveries, and fossils are plentiful, making it a darling of paleontologists, as well as amateur dinosaur observers.