Acrocanthosaurus, claw of hand Pachycephalosaurus Following the global mass extinction

Following the global mass extinction at the Silurian boundary

Duckbill skin & bone

Only about 10 complete and partial specimens have been found

including at least twenty partial to complete skulls

light weight

Acrocanthosaurus, claw of hand Pachycephalosaurus Following the global mass extinctionAcrocanthosaurus (meaning "high spine lizard" because of the spikes growing out of its spine) was a fierce predator that was roughly 30 40 feet (9 12 m) long and weighed about 5,000 pounds (2300 kg). It 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 and tail that may have formed a thick, fleshy sail on its back. It had powerful arms,