Acrocanthosaurus

***Acrocanthosaurus*** was a very large theropod carcharodontosaurid (carnosaur) dinosaur from North America during the Early Cretaceous Period about 112 million years ago, from the Carcharodontosauridae. It is one of the largest carnivores of said family, and also the fifth largest of North America.

## Description

*Acrocanthosaurus* was a large carnosaur theropod dinosaur that had a large head, many sharp teeth, strong arms, powerful back legs, and a long slender tail that balanced its body when it ran. It lived alongside the small raptor *Deinonychus*, some small ankylosaurs, and hunted large sauropods. *Acrocanthosaurus* had one feature that made it look very different from other theropods; the 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. It may represent an evolutionary link between the Late Jurassic *Allosaurus* and the gigantic Early Cretaceous *Carcharodontosaurus*. It was one of the largest bipedal carnivorous dinosaurs, with one mounted specimen reaching a length of possibly 11.5 meters (38 feet) and an estimated weight of 5.7 to 6.2 tonnes (6.3 to 6.8 tons), with an upper maximum weight of 7.25 t (7.99 tons) within the realm of possibility. Many of its vertebrae had high neural spines, though nowhere as high as those of *Spinosaurus*.
Scientists have debated why *Acrocanthosaurus* had a sail or a ridge along its back. Some think it released heat when the animal was too hot. It also may have been 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. There are other large tall-spined dinosaurs from Europe and Africa, but scientists don't know how *Acrocanthosaurus* is related to them. *Altispinax* had spines almost three-feet tall and *Spinosaurus* had six foot tall spines on its back. 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 three to five 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, possibly *Sauroposeidon*. When the sauropod footprints changed direction, so did those of *Acrocanthosaurus*. The outcome of this discovery shows that the *Acrocanthosaurus'* jaws were hanging onto one of the thighs of the sauropod while the it was running. The predator would then rip out a chunk of flesh and the sauropod later died of loss of blood and infection. This discovery concluded that *Acrocanthosaurus* was known for hunting large sauropods, something that most carnivorous theropods would never do.

## Classification

Acrocanthosaurus is classified in the superfamily Allosauroidea within the infraorder Tetanurae. This superfamily is characterized by paired ridges on the nasal and lacrimal bones on top of the snout and tall neural spines on the neck vertebrae, among other features. It was originally placed in the family Allosauridae with Allosaurus, an arrangement also supported by studies as late as 2000. Most studies have found it to be a member of the related family Carcharodontosauridae.

At the time of its discovery, Acrocanthosaurus and most other large theropods were known from only fragmentary remains, leading to highly variable classifications for this genus. J. Willis Stovall and Wann Langston Jr. first assigned it to the "Antrodemidae", the equivalent of Allosauridae, but it was transferred to the taxonomic wastebasket Megalosauridae by Alfred Sherwood Romer in 1956. To other authors, the long spines on its vertebrae suggested a relationship with Spinosaurus. This interpretation of Acrocanthosaurus as a spinosaurid persisted into the 1980s, and was repeated in the semi-technical dinosaur books of the time.

Tall spined vertebrae from the Early Cretaceous of England were once considered to be very similar to those of Acrocanthosaurus, and in 1988 Gregory S. Paul named them as a second species of the genus, A. altispinax. These bones were originally assigned to Altispinax, an English theropod otherwise known only from teeth, and this assignment led to at least one author proposing that Altispinax itself was a synonym of Acrocanthosaurus. These vertebrae were later assigned to the new genus Becklespinax, separate from both Acrocanthosaurus and Altispinax.

Most cladistic analyses including Acrocanthosaurus have found it to be a carcharodontosaurid, usually in a basal position relative to the African Carcharodontosaurus and Giganotosaurus from South America. It has often been considered the sister taxon to the equally basal Eocarcharia, also from Africa. Neovenator, discovered in England, is often considered an even more basal carcharodontosaurid, or as a basal member of a sister group called Neovenatoridae. This suggests that the family originated in Europe and then dispersed into the southern continents (at the time united as the supercontinent Gondwana). If Acrocanthosaurus was a carcharodontosaurid, then dispersal would also have occurred into North America. All known carcharodontosaurids lived during the early-to-middle Cretaceous Period.