As Laurasia and Gondwanaland broke into smaller continents, dinosaurs on the separated continents evolved differently. England and Belgium contain the best-studied Early Cretaceous rocks. The most famous herbivore of this time was Iguanodon. The remains of its smaller, speedier relatives Hypsilophodon, Valdosaurus, and Vectisaurus are more scarce. All these ornithopod dinosaurs were closely related to the Jurassic dinosaurs Othnielia, Dryosaurus, and Camptosaurus.
Ann Ronan Picture Library
Other plant-eaters from this area include the sauropod Pelorosaurus, with a long, slender upper-arm bone; it seems to have been a brachiosaurid. Craterosaurus is the only known stegosaur; the ankylosaur Hylaeosaurus seems to have been quite a bit more abundant than Craterosaurus. Armored dinosaurs were short and probably ate lower-growing plants. The small herbivore Stenopelix also lived during this period. It was possibly the earliest known ceratopsian. Yaverlandia is thought to be a very early pachycephalosaur.
Since North America was still joined to Europe (via Greenland), it had dinosaurs quite similar to those of Europe. Iguanodon is known from the Early Cretaceous rocks of the western United States. Hypsilophodon was also present. Huge sauropods were in decline; the stegosaurs were almost completely gone. They were replaced by ankylosaurs such as Hoplitosaurus from South Dakota and Silvisaurus from Kansas. Large predators, including Acrocanthosaurus, were also present.
Wyoming and Montana have the best-known North American Early Cretaceous dinosaur fauna. The bulky ornithopod Tenontosaurus is the best-known herbivore. It seems to have been hunted by packs of Deinonychus, a wolf-size predator famous for its sickle-shaped claws. Also found were the small predator Microvenator, the spiky armored Sauropelta, and the hypsilophodontid Zephyrosaurus.
Large ornithopods were not common in the Early Cretaceous of eastern Asia. The iguanodontid Probactrosaurus is thought to be close to the ancestry of the duckbilled dinosaurs. Of roughly the same age was a massive, large-nosed iguanodontid, Iguanodon orientalis. One common herbivore in Asia was Psittacosaurus; it was a small bipedal dinosaur. Armored plant-eaters were also common. One of the last stegosaurs, Wuerhosaurus, was a 25-foot-long plant-eater.
Preying upon these herbivores were large and small theropods. Kelmayisaurus was a megalosaurid that probably ate the armored Wuerhosaurus. Chilantaisaurus maortuensis could easily have held a struggling Probactrosaurus in the grip of its powerful front limbs.