Why do deinonychus eat iguanodon?

Answer 1

Deinonychus lived between 115 and 108 million years ago in North America, while Iguanodon lived between 126 and 125 million years ago in Europe. Thus, Deinonychus never would have encountered Iguanodon.

Fossil evidence shows that Deinonychus often ate the remains of Tenontosaurus, a 20+ foot long herbivore that weighed up to 2 tons. Whether the Deinonychus were scavenging or had hunted the Tenontosaurus in a pack is unknown. Even if it did hunt large herbivores in a pack, though, Iguanodon was nearly twice as large as Tenontosaurus, so in the case that some Deinonychus did come across an Iguanodon, it probably would have been very difficult for a pack of Deinonychus to hunt and kill an adult Iguanodon. A young Iguanodon would have been easy prey for Deinonychus, though.