Are iguanodons and iguanas related?

Iguanodons (genus Iguanodon) and iguanas (subfamily Iguaninae) are related only insofar as both are reptiles—but so are turtles and snakes. Iguanas are in the lizard family and are only distantly related to dinosaurs like iguanodons on the evolutionary tree. Although their similar names suggest affinity, their connection stems from the appearance of their teeth and the early discovery of iguanodon fossils. The name iguanodon means “iguana tooth.”

When husband-and-wife amateur paleontologists Gideon Mantell and Mary Ann Mantell discovered fossilized teeth in Sussex, England, in 1822, they tried to identify them. Gideon Mantell visited the Hunterian Museum in London where he saw an iguana skeleton and noted that the fossilized teeth appeared to be much larger versions of iguana teeth. Hence the name of the newly discovered creature, which Mantell calculated based on scale would be up to 18 meters (60 feet) in length. Further research has concluded that iguanodons were as long as 9 meters (30 feet), far larger than iguanas, the largest of which are 2 meters (6.6 feet) long.

The discovery of iguanodon fossils had a significant role in the development of dinosaur paleontology. In 1825 Gideon Mantell published his findings on Iguanodon, which he described as a large herbivorous reptile. One year earlier, in 1824, William Buckland published a scientific description of Megalosaurus, which he conjectured was a type of giant lizard. These were the first two published findings about the ancient reptiles that would later be called dinosaurs. In 1842 paleontologist Richard Owen formally recognized the scientific classification of dinosaurs (Dinosauria) based on the examples of Megalosaurus, Iguanodon, and Hylaeosaurus, which Gideon Mantell had also discovered.

Iguanas did not evolve from iguanodons. Iguanas are part of the lizard family Iguanidae and Squamata order. Dinosaurs such as iguanodons belong to the archosaur subclass of reptiles, of which the only living descendants are creatures such as crocodiles and birds—not iguanas.