Iguanodon was a massive herbivorous long-tailed bipedal dinosaur of the genus Iguanodon, common in Europe and N Africa in Jurassic and Cretaceous times. They were bulky and could shift from bipedality to quadrupedality. The numerous specimens of this genus, including nearly complete skeletons from two well-known bonebeds, have allowed researchers to make informed hypotheses regarding many aspects of the living animal, including feeding, movement, and social behavior. Louis Antoine Marie Joseph Dollo (December 7, 1857 - April 19, 1931) was a French-born Belgian paleontologist, known for his work on dinosaurs. From 1882-85, while he was docent of the vertebrate fossil section of the Royal Institute, he worked on reconstructing the skeletons of the Iguanodons. The first one was assembled in the interior of an unused church that he was using as a workshop. Around 1890, he formulated a hypothesis on the irreversible nature of evolution, known later as "Dollo's Law." According to his hypothesis, a structure or organ lost during the course of evolution would not reappear in that organism. He is credited with establishing the principles of paleobiology. He died in 1931 at the age of 73.