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Acrocanthosaurus (meaning "High Spined Lizard") is a genus of dinosaur with an original invalid name of Acrocanthus. In the U.S it is found in Oklahoma, Texas, and Arizona but, it's teeth were found in Maryland. It is slightly smaller than Gigantosaurus so, it is almost the biggest theropod ever found. The skull of Acrocanthosaurus is long, narrow, and low.

Until recently, Acrocanthosaurus was not well known. In some ways it looked like many other meat-eating dinosaurs. It had a large head, many sharp teeth, short arms, powerful back legs, and a long slender tail that balanced its body when it ran. But Acrocanthosaurus had one feature that made it look very different; it had a tall "sail" along its neck, back, and tail. The sail was formed by very tall spines on the bones of the spine (vertebrae). Some of these spines were over a foot tall; the spines of Tyrannosaurus were only half that tall.

Scientists have debated why Acrocanthosaurus had a sail along its back. Some think it released heat when the animal was too hot. It was probably used for display to make the animal look bigger when it faced rivals for territories or mates. This is much like a house cat fluffing up its fur and arching its back to make itself look bigger.

No complete skeleton of Acrocanthosaurus has been found. Instead, paleontologists have built the dinosaur from parts of three skeletons. One skeleton had a three-foot-long skull. An adult Acrocanthosaurus was about ten feet tall at the hips and weighed between two and four tons.

Scientists have found footprints probably made by Acrocanthosaurus in several places in Texas. In one place, it looks like an Acrocanthosaurus stalked a large sauropod across a mud flat. When the sauropod footprints changed direction, so did those of Acrocanthosaurus. The outcome of the chase is not known; the end of the trackway has never been found.

There are other tall-spined meat-eating dinosaurs from Europe and Africa, but paleontologists do not know how Acrocanthosaurus is related to them. Altispinax had spines almost three feet tall and Spinosaurus had spines six feet tall.