The function of the nose hump isn’t known, but the prominent facial features may have been brightly colored or boldly patterned
The iguanodont lineage first emerged at the end of the Jurassic Period and quickly radiated across the northern continents throughout the Early Cretaceous. They evolved from ancestors called hypsilophodonts which looked like kangaroos or ground birds. They were present in almost all environments throughout the age of dinosaurs but were usually minor players in their ecosystems.
The key to the success of the iguanodonts lies their teeth. In the line leading to the iguanodonts, the gaps between their teeth gradually disappeared, so that the dozens of teeth in each jaw were tightly packed together and worked as a kind of “super-tooth” known as a dental battery. Their dental batteries let them do something that no other reptile could do: chew their food, especially tough plant material.
Iguanodonts were larger than their ancestors, ranging in size from about pony-sized to elephant-sized. Most walked on all fours at least some of the time, holding their spike thumbs clear of the ground. One lineage within the iguanodonts called the hadrosaurs, developed even more efficient dental batteries, and lost their thumbs altogether. The hadrosaurs underwent a second nearly global radiation at the end of the Cretaceous Period, spreading across all the northern continents, as well as South America.
Many iguanodont and hadrosaur species are known from large bone beds, suggesting that they lived in large groups. In the Cretaceous Period, these grazing herbivores filled roles now taken by horses, elk, and bison.
The new species shows that the evolution of the iguanodonts wasn’t a simple line from the hypsilophodonts to the hadrosaurs, but instead a complex branching tree full of unique and wide-ranging lineages. Gates and colleagues found that Choyrodon wasn’t particularly closely related to its look-alike Altirhinus. Instead, it was found to be close kin to Eolambia carolejonesae, known from rocks in Utah formed about 10 million years later.
The rocks where Choyrodon were discovered, the Khuren Dukh Formation, have only a few other dinosaurs known. Its discovery sheds light onto the rare and understudied fauna of Mongolia in the Early Cretaceous. Mongolia’s deserts seem to hold untold numbers of dinosaur skeletons, and there is surely more to come.
Read the original research in PeerJ.