Dr. Bob on Marsh's "Half-A-Chicken"
Othneil Charles Marsh originally discovered Nanosaurus in 1878. He was sure it was a dinosaur, the smallest ever found. He was very proud. He did notice two strange features as he has drawing and describing the jaw: all the tooth crowns lined up and they all seem to be held by tall roots like a picket fence. That's not standard dinosaur equipment. It's more like the arrangement in lizards.
Another puzzle became obvious in the 1880's The Nano jaw didn't have a notch at the front where an extra bone, the predentary, would attach. All the other Bird-Hipped herbivores had the notch.
Marsh dug a new herbivorous dinosaur at Como in 1879, a skeleton about the size of a Rhea, the long-legged ground bird of the Argentine Pampas. This fast-running veggiesaur had tooth crowns that did not line up. And it had a big notch for the predentary. Therefore it was NOT a Nanosaurus. But Marsh never named this other species, so Peter Galton used this fine specimen to define the genus Othnielosaurus in Marsh's honor.
Meanwhile, starting in the 1970s, my crew found dozens of specimens from a closely related dino; we named it Drinker nisti. Drinker as an adult was way bigger than Nanosaurus, as large as a big wild turkey. But still far smaller than an Othnielosaurus. The name honored Edward Drinker Cope. Many Drinkers, young and adult, were packed together in small sections of mudstone indicating the possibility of burrows.
Drinker had an unusual skull shape -- big and boxy. And its molars had an extra cusp. All the specimens are from the topmost layer in the Morrison Formation
Soooooooooooooooooo..........the small to mid-sized fast running plant eaters produced a variety of lively species during the final days of the Jurassic.