November 17. Onithopods

Hypsilophodon drawing by ArthurWesaley,
used under Creative Commons license. 

The ornithopods were some of the most successful and diverse dinosaurs of the Cretaceous. They typically had three toes, but some had four, and despite the name, which means “bird foot,” ornithopods were not in the dinosaur lineage that led to birds. Like many types of dinosaur, they began during the Jurassic, but in Cretaceous time herbivorous ornithopods dominated many landscapes. They were typically smaller than the huge Sauropods, on the order of three to ten feet long, though a few species grew to perhaps 50 feet in length. 

Hypsilophodon, discovered on the Isle of Wight in England in 1849, was about 2 meters or 6 feet long and ran on two legs as most ornithopods did, although they probably functioned as quadrupeds at times. Its skeletal anatomy indicates that it was a ground-living animal that could probably run pretty fast – presumably for defensive escape, like a deer or gazelle, since it was a plant-eater. Because of their herbivorous natures, many Cretaceous ornithopods had lost most of their front teeth, which were replaced by a hard, beak-like mouth structure.   

Hadrosaur photo by Lisa Andres from Riverside, USA,
used under Creative Commons license.

The culmination of evolution among the ornithopods and their kin was probably the hadrosaurs – the duck-billed dinosaurs that were abundant in late Cretaceous time. Some hadrosaurs really did have a face that was elongated into a bill-like structure presumably used for snagging leaves and twigs, but they did have grinding teeth in the back of the mouth. Duck-billed dinosaurs also had complex crests on the tops of their heads – at least some species did, but some had no ornamentation at all. The role in life of the hollow crests has been discussed for years, and I think today the consensus is that they may have been used for both audible hooting and as a visual display.

Hadrosaurs probably descended from Iguanodons or their relatives, which we discussed earlier this month. They lived in what are now Asia, Europe, and North America and are dated mostly to the last 10 or 15 million years of the Cretaceous period. All went extinct at the end of the Cretaceous.

—Richard I. Gibson

Reference: Holtz, Thomas R. Jr. (2012) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages

Hypsilophodon drawing by ArthurWesaley, used under Creative Commons license. 

Hadrosaur photo by Lisa Andres from Riverside, USA, used under Creative Commons license.