Acrocanthosaurus atokensis

Acrocanthosaurus had unusually tall neural spines along its vertebrae—extending from the neck through the back and tail—that formed a low sail or ridge along the animal's dorsal surface. The function of this structure remains debated, with proposed roles including thermoregulation, visual display, or serving as attachment sites for powerful neck and back musculature.

Fossils are known principally from Oklahoma and Texas, with the species name "atokensis" referring to Atoka County, Oklahoma. Specimens have also been reported from nearby states, and notable fossils are housed at institutions including the North Carolina Museum of Natural Sciences, which displays a nearly complete skeleton.

Acrocanthosaurus is classified within Carcharodontosauridae, a family of large allosauroid theropods that also includes Giganotosaurus from South America and Carcharodontosaurus from North Africa. It was once mistakenly thought to be a tyrannosaur or a spinosaur relative, but cladistic analyses have firmly placed it within the carcharodontosaur lineage.

Acrocanthosaurus was among the largest predatory dinosaurs in North America, with length estimates of approximately 11 to 12 meters and a weight of several tonnes, making it comparable in overall size to Tyrannosaurus rex. However, Acrocanthosaurus lived tens of millions of years earlier, during the Early Cretaceous rather than the latest Cretaceous.