Scientists believe they've recovered the oldest dinosaur bones ever found. The find was made by scientists digging in Madagascar. What they've unearthed are the jawbones of two kangaroo-sized dinosaurs called prosaurapods, plant-eaters with small heads and long necks that could walk on two or four legs. They're not a new species, but by finding the "oldest ever" example, at least by a few million years, scientists will be able to glean more about how dinosaurs, and all mammals, evolved from reptiles. Circumstantial evidence dates the fossils to the early Triassic period, 230 million years ago. The report of the find is published in the journal Science.