Here are the original pencils to the Brett Booth Spinosaurus in Thunder Lizards! (page 52.) Spinosaurus is called "spiny lizard" because it had a series of large neural spines up to 6 feet (1.8 m) long coming out of its back vertebrae, probably forming a sail-like fin that may have helped in thermoregulation, mating rituals and/or intraspecies rivalry. Spinosaurus had a relatively flexible upper spine (these vertebrae had modified ball-and-socket-joints) so it could arch its back somewhat, perhaps being able to spread the sail (like opening the ribs of a fan).

Spinosaurus was bipedal (it walked on two legs). It was about 40-50 feet long (12-15 m) and weighed 4 tons or more (some paleontologists estimate it weighed up to perhaps 8 tons); it is the largest known spinosaurid (a type of large, meat-eating dinosaur). It had a large head with sharp, straight, non-serrated teeth in powerful, crocodile-like jaws. Its arms were smaller than its legs but were larger than the arms of most other theropods. It may have gone on all fours at times.