Which dinosaur was the first to be scientifically named, in 1824?

The first dinosaur genus to be validly named was Megalosaurus, in 1824.

English geologist William Buckland formally presented Megalosaurus to the Geological Society of London on 20 February 1824. The name means “great lizard,” reflecting the early belief that the animal was a giant reptile resembling a modern lizard. Its fossils came from Middle Jurassic rocks in Oxfordshire, England, and included parts of the lower jaw and other bones.

Megalosaurus was not reconstructed accurately at first. Buckland imagined it as a large, four-legged animal, and early scientists had only a small collection of bones to work with. In 1842, Richard Owen placed Megalosaurus alongside Iguanodon and Hylaeosaurus in Dinosauria, helping establish dinosaurs as a distinct group.

The wording can cause a historical confusion. Fossil dinosaur bones had been described earlier, and Streptospondylus was scientifically described in 1808, but Megalosaurus was the first dinosaur genus to receive a valid formal name. Tyrannosaurus and Diplodocus were named much later; Iguanodon was named in 1825.