Iguanodons were large, plant-eating dinosaurs. These creatures hold a notable place in the history of paleontology, being among the earliest dinosaurs formally identified and studied. Their discovery helped lay the groundwork for understanding the diverse forms of ancient reptiles that once roamed Earth.
Unique Physical Traits
Iguanodons were substantial herbivores, measuring around 9 to 11 meters (30 to 36 feet) in length and weighing around 3.4 to 4.5 metric tons (3.7 to 5.0 short tons). Their robust build included strong hind limbs, supporting their weight and allowing movement. While capable of walking on all fours, they could also shift to a bipedal stance, especially for running or browsing higher vegetation.
A defining feature of Iguanodons was the distinctive thumb spike, a conical projection on each hand. Early reconstructions mistakenly placed this spike on the dinosaur’s nose, but later fossil discoveries clarified its true position on the hand. The spike’s function is debated, with theories suggesting its use for defense against predators, for breaking into seeds and fruits, or even for stripping foliage from tree branches. Their hands also featured three central fingers designed to bear weight, along with an elongated, flexible fifth finger possibly used for manipulating objects or foraging for food.
The skull of an Iguanodon was large, tall, and narrow, ending in a toothless beak. Behind the beak, their mouths contained teeth resembling those of modern iguanas. These specialized teeth were ridged and structured to provide a grinding action, similar to mammalian chewing, enabling them to process tough plant material effectively. Unlike some other herbivorous dinosaurs, Iguanodon typically had only one replacement tooth at a time for each position.
Habitat and Diet
Iguanodons roamed the Earth during the Early Cretaceous period, around 126 to 122 million years ago. Their fossils have been uncovered across various continents, including Europe (notably England, Belgium, Germany, and Spain), North Africa, North America, and parts of Asia and Australia. They inhabited diverse environments, including lush floodplains, forests, coastal areas, and open grasslands.
As herbivores, Iguanodons primarily consumed plant material, using their specialized dental structure to process tough vegetation. Their diet likely included plants common during the Early Cretaceous, such as ferns, cycads, and conifers. Larger Iguanodon species could reach foliage up to 4 to 5 meters (13 to 16 feet) high, accessing a broad range of food sources, from low-lying plants to tree foliage. Their continuous tooth replacement ensured they maintained an efficient grinding mechanism throughout their lives.
The Story of Its Discovery
Iguanodon’s discovery began in the early 1820s in England with Gideon Mantell, an English physician and geologist. His wife, Mary Ann Mantell, found fossilized teeth in a pile of roadside rubble in Sussex in 1822. These teeth, unlike any known animal, Mantell recognized their resemblance to those of a modern iguana. This comparison led him to name the creature “Iguanodon” in 1825, meaning “iguana tooth,” marking it as the second dinosaur formally described after Megalosaurus.
Mantell’s initial reconstructions, based on fragmentary remains, depicted Iguanodon as a quadrupedal, rhinoceros-like creature with the thumb spike on its nose. This early interpretation influenced public displays, such as the Crystal Palace dinosaur sculptures in London in 1854. In 1842, anatomist Richard Owen, using Iguanodon, Megalosaurus, and Hylaeosaurus, formally coined the term “Dinosauria,” establishing dinosaurs as a distinct group of reptiles. Subsequent discoveries, like complete skeletons found in Bernissart, Belgium, in 1878, provided a more accurate understanding of Iguanodon’s anatomy, correctly placing the thumb spike on its hand and revealing its facultative bipedal posture.