Iguanodon

MEANING: Iguana tooth

PERIOD: Early Cretaceous

CONTINENT: Europe

Iguanodon is one of the first scientifically well-known dinosaurs. Adults are estimated to have measured about 9 m long, and weighed around 4 t. Iguanodon had a toothless beak, and in the back of the mouth they had teeth that resembled those of iguanas, as the name suggests, but were much larger and more closely packed.

Iguanodon is from the Early Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Early Cretaceous making up roughly the first half, lasting from about 143 to 100 million years ago. The poles were ice-free, due to the relatively warm climate, and forests extended into high latitudes. The continued breakup of the continents created new coastlines and isolated landmasses, influencing the evolution of distinct dinosaur faunas.

It was a time of transition, as many groups of animals and plants began to take on more modern forms while others declined or disappeared. Pterosaurs continued to thrive, though early birds were becoming more diverse and widespread. Mammals remained small but adapted to a variety of ecological niches. In the oceans, ichthyosaurs and plesiosaurs were common, and early mosasaurs began to appear.

Dinosaurs remained the dominant land animals, with groups like iguanodontians, spinosaurids, and carcharodontosaurids rising to prominence. While sauropods declined in some regions, they remained abundant in the Southern Hemisphere. The first true ceratopsians appeared, and ankylosaurs replaced stegosaurs in their niche. Dromaeosaurs and other small theropods diversified. During this time, the first flowering plants evolved, gradually changing global ecosystems by providing new food sources for herbivores.

Iguanodon is an iguanodontian. Iguanodontia was an important branch of the ornithopoda, a group of herbivorous dinosaurs that would become one of the most successful clades of the Cretaceous. These dinosaurs first appeared in the Late Jurassic as small bipedal grazers, but diversified through the Early Cretaceous, gradually increasing into larger more robust forms. While the more derived hadrosaurs of the Late Cretaceous became highly specialized for chewing tough plant material, basal iguanodontians retained a mix of primitive and advanced traits. They were among the first large-bodied ornithopods to spread widely across the Northern Hemisphere, with fossils found in Europe, North Africa, and Asia.

Early iguanodontians possessed powerful hind limbs for efficient bipedal movement but could also walk on all fours when foraging. One of their most distinctive features was their unique hand structure, which included a stiff, spike-like thumb that may have been used for defense or breaking apart tough vegetation. Although they lacked the fully developed dental batteries of later hadrosaurs, their teeth were already adapted for efficient plant processing, giving them an evolutionary advantage as herbivores. These adaptations laid the groundwork for the eventual dominance of hadrosaurs, which would expand into even more diverse habitats and continue to thrive until the end of the Cretaceous.