Which type of dinosaur was the second type to be formally named based on fossil specimens?

Iguanodon, named in 1825, is a genus of ornithopod dinosaur that existed roughly halfway between the first of the swift bipedal hypsilophodontids of the mid-Jurassic and the duck-billed dinosaurs of the late Cretaceous. Distinctive features include large thumb spikes, which were possibly used for defense against predators, combined with long prehensile fifth fingers able to forage for food.

The genus was named in 1825 by English geologist Gideon Mantell but discovered by William Harding Bensted, based on fossil specimens found in England, some of which were subsequently assigned to Mantellodon. Iguanodon was the second type of dinosaur formally named based on fossil specimens, after Megalosaurus. Together with Megalosaurus and Hylaeosaurus, it was one of the three genera originally used to define Dinosauria.