Anatomy: Acrocanthosaurus was 30-40 feet (9-12 m) long and weighed about 5,000 pounds (2300 kg). This theropod dinosaur had a big head, with a 4.5-foot (1.4 m) long skull and 68 thin, sharp, serrated teeth. It had 17-inch (43 cm) spikes extending from its vertebrae along the neck, back, and tail. These spikes may have been covered with skin, forming a thick, fleshy sail along its back. This predator had powerful arms; each hand had three fingers equipped with long, sickle-like claws.

When it Lived: Acrocanthosaurus lived during the early Cretaceous period, about 115-105 million years ago.

Fossils: Acrocanthosaurus fossils have been found in Oklahoma, Texas, and Utah (in the USA). Many fossilized tracks have also been found.