Acrocanthosaurus was a bipedal carnivorous dinosaur that lived in what is now North America during the Early Cretaceous period (115-110 million years ago). At nearly 40 feet long and 6 tons, it was the largest predator of its time. Like most bipedal theropods, the forelimbs were too small to have reached the ground, and so were not used for walking. Partial skeletons of Acrocanthosaurus were first discovered in Oklahoma in the early 1940s and named in 1950. Because a lot of the bones were missing, we weren't sure exactly what Acroacanthosaurus looked like. In the 1990s, much more complete skeletons were discovered, providing more information on the unusual spines on the backbone, and allowing us to understand how the front limbs were used for hunting. Scientific Name: Acrocanthosaurus, meaning"high spined lizard", referring to the unusually tall spines on the vertebrae of the back.