Fossil bones of the huge herbivorous dinosaurs known as sauropods were first discov-
ered and studied between 1840 and 1880, providing evidence for the gargantuan
dimensions of the adults. The shape of sauropod teeth suggested what they ate. But
aside from trackways, or series of fossilized footprints — which established that sauro-
pods at least occasionally lived in herds — fossils incorporating direct evidence of other
behavior, such as reproductive behavior, have been almost nonexistent. Because no
modern land animals even approach sauropod size, scientists have also lacked a living
analogue to use as a guide to possible sauropod behavior. Until the recent discovery of
fossilized sauropod nesting grounds, scientists were thus uncertain whether sauropods
laid eggs or gave birth to live young.