Anomoepus gracillimus is the name assigned to footprints in the Late Triassic beds. All four feet have left impressions. The smaller forefeet have five toes, whereas the larger hind feet have three toes. There is also an impression which might indicate where the creature rested. The first to be discovered, amongst others, was by a farm boy, Pliny Moody. E.B. Hitchcock, a clergyman, described the Anomoepus footprints and others as evidence of ancient birds. They have since been identified as belonging to a dinosaur, probably an ornithopod, as indicated by the number of toes and the absence of claws on the rear digits. Anomoepus is not considered diagnostic, that is, it is the name of the footprint, not of the dinosaur, the identity of which remains unknown.
Ornithopoda means “bird feet”, from the Greek ornis (“bird”) and pous (“feet”); this refers to their characteristic three-toed feet, although many early forms retained four toes. They were also characterized by having no armor, the development of a horny beak, an elongated pubis that eventually extended past the ilium, and a missing hole in the lower jaw. A variety of ornithopods and related cerapods had thin cartilaginous plates along the outside of the ribs; in some cases, these plates mineralized and were fossilized. The function of these intercostal plates is unknown.
Three-toed Iguanodon feet
The early ornithopods were only about 1 meter (3 feet) long, but probably very fast. They had a stiff tail, like the theropods, to help them balance as they ran on their hind legs. Later ornithopods became more adapted to grazing on all fours; their spines curved, and came to resemble the spines of modern ground-feeders like the bison. As they became more adapted to eating while bent over, they became semi-quadrupedal; still running on two legs, and comfortable reaching up into trees; but spending most of their time walking or grazing while on all fours.
Later ornithopods became larger, but never rivaled the incredible size of the long-necked, long-tailed sauropods that they partially supplanted; the largest, like the Edmontosaurus and Shantungosaurus, never grew far beyond 15 meters (50 feet).