Period: Middle Jurassic

Order, Suborder, Family: Saurischia, Sauropodomorpha, Cetiosauridae

Location: Europe (England), Africa (Morocco)

Length: 60 feet (18 meters)

Cetiosaurus was a heavy sauropod. It looked much like Diplodocus and Apatosaurus, which may be its descendants. This is the best-known sauropod from England, where dinosaurs were first studied. Only the limbs, pelvis, and the greater part of the tail are known. The vertebrae are massive and do not have air pockets that reduce weight, as are found in most other sauropods. Like the legs of other sauropods, the limbs of Cetiosaurus were like pillars, and the tail was long and heavy. Cetiosaurus probably weighed up to 30 tons. It was one of the most primitive sauropods.

Cetiosaurus was described in 1841 and was the first sauropod dinosaur described. Cetiosaurus, which means "monster reptile" or "whale reptile," was the largest land animal known at the time, much larger than Iguanodon and other prehistoric reptiles. It was about the same size as the North Atlantic great whales. Cetiosaurus was thought to be a crocodile and was later confused with Iguanodon, an Early Cretaceous dinosaur.

Some paleontologists think another British sauropod, Cetiosauriscus, belongs to this genus. Bones in the tail of Cetiosauriscus, called "chevrons," resemble those of Diplodocus. If true, there is a close relationship between the families Cetiosauridae and Diplodocidae. This would show a connection between dinosaurs in Morocco, England, and North America during the Jurassic.