The Allosaurus, the "different lizard", was certainly one of the fiercest predators of the late Jurassic. He could measure up to 12 meters long but models of the famous A. fragilis specimen "Big Al" (the one we have in the Morian Paleontology Hall!) suggest the dinosaur weighed more than 3,300 pounds in adulthood. Allosaurus gets it's name from its vertebrae, which were different from any other dinosaur known at the time of its discovery in 1877. Specifically, some of the vertebrae of Allosaurus fragilis (Latin for "fragile") were concave on both sides and contained shallow cavities, giving them an hourglass shape- these features reduced the bones' strength, while making them lighter. The hollow spaces in these neck and anterior back vertebrae are also found in modern birds and believed to have contained air sacs for respiration.