Ornithopods - The Small, Herbivorous Dinosaurs

The Evolution and Behavior of Ornithopod Dinosaurs

Muttaburrasaurus, a classic ornithopod of late Cretaceous Australia (Australian Museum).

In their own way, ornithopods--the small, mostly two-legged herbivorous dinosaurs of the Mesozoic Era--have had a disproportionate impact on the history of paleontology. By a geographical fluke, many of the dinosaurs dug up in Europe in the early 19th century happened to be ornithopods (the most noteworthy being Iguanodon), and today more ornithopods are named after famous paleontologists than any other kinds of dinosaur.

(See a gallery of ornithopod dinosaur piotures and profiles.)

Ornithopods (the name is Greek for "bird-footed") are one of the classes of ornithischian ("bird-hipped") dinosaurs, the others being pachycephalosaurs, stegosaurs, ankylosaurs and ceratopsians. The most well-known subgroup of ornithopods are the hadrosaurs, or duck-billed dinosaurs, which are discussed in a separate article; this piece focuses on the smaller, non-hadrosaur ornithopods.

Technically speaking, ornithopods (including hadrosaurs) were plant-eating dinosaurs with bird-shaped hips, three- or four-toed feet, powerful teeth and jaws, and a lack of the anatomical "extras" (armor plating, thickened skulls, clubbed tails, etc.) found on other ornithischian dinosaurs. The earliest ornithopods were exclusively bipedal, but the larger species of the Cretaceous period spent most of their time on all fours (though it's conjectured that they could run on two feet if they had to get away in a hurry).

Ornithopod Behavior and Habitats

Paleontologists often find it helpful to infer the behavior of long-extinct dinosaurs from the modern creatures they most resemble. In that respect, the modern analogs of ancient ornithopods seem to be herbivorous mammals like deer, bison, and wildebeests. Since they were relatively low on the food chain, it's believed that most genera of ornithopods roamed the plains and woodlands in herds of hundreds or thousands, to better protect themselves from raptors and tyrannosaurs, and it's also likely that they took care of their hatchlings until they were able to fend for themselves.

Ornithopods were widespread geographically; fossils have been dug up on every continent except Antarctica. Paleontologists have noted some regional differences between genera: for example, Leaellynasaura and Qantassaurus, which both lived in near-Antarctic Australia, had unusually large eyes, presumably to make the most of the limited sunlight, while the north African Ouranosaurus may have sported a camel-like hump to help it through the parched summer months.

As with many types of dinosaurs, our state of knowledge about ornithopods is constantly changing. For example, recent years have seen the discovery of two enormous genera, Lanzhousaurus and Lurdusaurus, which lived in mid-Cretaceous Asia and Africa, respectively. These dinosaurs weighed about 5 or 6 tons each, making them the heaviest ornithopods until the evolution of plus-sized hadrosaurs in the later Cretaceous--an unexpected development that has caused scientists to revise their views of ornithopod evolution.

Ornithopod Controversies

As noted above, ornithopods featured prominently in the early development of paleontology, thanks to the fact that an unusual number of Iguanodon specimens (or herbivores that closely resembled Iguanodon) wound up fossilized in the British Isles.

In fact, Iguanodon was only the second dinosaur ever to be officially named (the first was Megalosaurus), one unintended consequence being that subsequent Iguanodon-like remains were assigned to that genus, whether they belonged there or not.

To this day, paleontologists are still undoing the damage. An entire book could be written about the slow, laborious untangling of the various "species" of Iguanodon, but suffice it to say that new genera are still being coined to make room for the reshuffling. For example, the genus Mantellisaurus was created as recently as 2006, based on its obvious differences from Iguanodon (to which it's still closely related, of course).

Mantellisaurus evokes another long-standing fracas in the hallowed halls of paleontology. This ornithopod was named after Gideon Mantell, whose original discovery of Iguanodon in 1822 was appropriated by the egotistical Richard Owen.

Today, Owen has no dinosaurs bearing his name, but Mantell's eponymous ornithopod goes a long way toward correcting a historical injustice.

The naming of small ornithopods also figures in another famous paleontological feud. During their lifetimes, Edward Drinker Cope and Othniel C. Marsh were mortal enemies, the result of an Elasmosaurus head being placed on its tail rather than its neck (don't ask). Today, both of these paleontologists have been immortalized in ornithopod form--Drinker and Othnielia--but there's some suspicion that these dinosaurs may actually have been two species of the same genus!

Finally, there is now solid evidence that at least some ornithopods--including the late Jurassic Tianyulong and Kulindadromeus--had feathers. What this means, vis-a-vis feathered theropods, is anyone's guess; perhaps ornithopods, like their meat-eating cousins, possessed warm-blooded metabolisms and needed to be insulated from the cold.