Oldest Known Dinosaur Embryos

The 8-inch-long (20-centimeter-long) youngster, for example, had long front legs for walking on all fours, and its overall body proportion—such as a short snout—made it "look like a dwarf version of a sauropod dinosaur," the largest animals to walk Earth. The babies would have lost these traits as they matured.

The sharpest look yet at the oldest known dinosaur embryos (pictured, one of the eggs and its inhabitant) has revealed some "big surprises." For one thing, the 190-million-year-old babies of Massospondylus—a two-legged dinosaur that preceded the well-known sauropods, such as Diplodocus—do not resemble their parents, according to study co-author Hans-Dieter Sues, a paleontologist at the National Museum of Natural History in Washington, D.C.

The discovery suggests Massospondylus had characteristics that "foreshadowed" the later look of the sauropods.