Herd of reptiles Fiorelli and his colleagues began excavating in northwest Argentina two years ago and quickly uncovered fossilized poop - known as coprolites - by the bucket load. These coprolites date back to the middle Triassic, 240 million years ago. In this era, small dinosaurs were just beginning to appear, but the world belonged to strange mammal-like reptiles, including the famous sail-backed Dimetrodon. (Gallery: The Diversity of Dinosaur Ancestors)
In some areas, there were as many as 94 rounded fossil poops every 10 square feet (1 square meter). The coprolites varied in size from just about half an inch (1 centimeter) in diameter to more than a foot (35 cm) wide. Such variation in such a small area strongly suggested a herd of young and old animals living together, defecating communally.
In total, the researchers found eight separate latrine spots. Most of the coprolites were oval or spherical, with a few "sausagelike" outliers and a few shaped like cow patties. The only animal large enough to produce dung balls more than a foot in diameter in this region was Dinodontosaurus, a beaky, tusked bruiser that could weigh up to 6,600 pounds (3,000 kilograms). In comparison, a modern African female bush elephant weighs about 8,000 lbs. (3,600 kg).