Acrocanthosaurus , meaning 'high-spined lizard') is a genus of theropod dinosaur
Acrocanthosaurus is a bipedal carnivore. As the name suggests, it is best known for the high neural spines on many of its vertebrae, which supports a ridge of muscle over the animal's neck, back and hips. Acrocanthosaurus is one of the largest theropods, approaching 12 meters (40 ft) in length, and weighing up to 6.17 metric tons (6.8 short tons).
Although slightly smaller than gigantic relatives like Giganotosaurus, Acrocanthosaurus is still among the largest theropods ever to exist. The longest individuals measure 11.5 meters (38 ft) from snout to tail tip and weigh an estimated 6,177 kilograms (13,618 lb). Its skull alone is nearly 1.3 meters (4.3 ft) in length. The skull of Acrocanthosaurus, like most other allosauroids, is long, low and narrow. The weight-reducing opening in front of the eye socket (antorbital fenestra) is quite large, more than a quarter of the length of the skull and two-thirds of its height. The outside surface of the maxilla (upper jaw bone) and the upper surface of the nasal bone on the roof of the snout were not nearly as rough-textured as those of Giganotosaurus. Long, low ridges arise from the nasal bones, running along each side of the snout from the nostril back to the eye, where they continue onto the lacrimal bones. This is a characteristic feature of all allosauroids. Unlike Allosaurus, there is no prominent crest on the lacrimal bone in front of the eye. The lacrimal and postorbital bones meet to form a thick brow over the eye, as seen in carcharodontosaurids and the unrelated abelisaurids. Nineteen curved, serrated teeth line each side of the upper jaw. Acrocanthosaurus teeth are wider than those of Carcharodontosaurus and do not have the wrinkled texture that characterized the carcharodontosaurids. The dentary (tooth-bearing lower jaw bone) is squared off at the front edge, as in Giganotosaurus, and shallow, while the rest of the jaw behind it becomes very deep. Acrocanthosaurus and Giganotosaurus shares a thick horizontal ridge on the outside surface of the surangular bone of the lower jaw, underneath the articulation with the skull. The most notable feature of Acrocanthosaurus is its row of tall neural spines, located on the vertebrae of the neck, back, hips and upper tail, which can be more than 2.5 times the height of the vertebrae from which they extend. Other dinosaurs also have high spines on the back, sometimes much higher than those of Acrocanthosaurus. For instance, the unrelated Spinosaurus has spines nearly 2 meters (6.5 ft) tall, about 11 times taller than the bodies of its vertebrae. Rather than supporting a skin 'sail' as seen in Spinosaurus, the lower spines of Acrocanthosaurus have attachments for powerful muscles like those bison. All of its cervical (neck) and dorsal (back) vertebrae have prominent depressions (pleurocoels) on the sides, while the caudal (tail) vertebrae bare smaller ones. This is more similar to carcharodontosaurids than to Allosaurus.
Aside from its vertebrae, Acrocanthosaurus has a typical allosauroid skeleton. Acrocanthosaurus is bipedal, with a long, heavy tail counterbalancing the head and body, maintaining its center of gravity over its hips. Its forelimbs are relatively shorter and more robust than those of Allosaurus but are otherwise similar: each hand bares three clawed digits. Unlike many smaller fast-running dinosaurs, its femur is longer than its tibia and metatarsals, suggesting that Acrocanthosaurus is not a fast runner. Unsurprisingly, the hind leg bones of Acrocanthosaurus are proportionally more robust than its smaller relative Allosaurus. Its feet has four digits each, although as is typical for theropods, the first is much smaller than the rest and does not make contact with the ground.