What species is the oldest dinosaur? To answer that, we have to define what a dinosaur is. Sure, a dinosaur is an extinct reptile, but there were other reptiles before and after dinosaurs. Scientists have defined dinosaurs by their hips and legs. What distinguished dinosaurs from the crocodile-like reptiles of the ancient world was the converting of the vertebrae into sacra, modified structures that allowed reptiles to point their back legs in one direction, allowing them to walk forward on two legs. Sure, not all dinosaurs were bipeds, but they all descended from those that evolved that ability.
Using that definition the oldest dinosaur was Nyasasaurus, according to fossils dating back around 243 million years. Dinos were getting off the ground when a mass extinction event 200 million years ago left them as the dominant animal for a period of 135 million years. Compare that to humans, who have only been around a few million years, and have only recorded our history for a few thousand years, which is just a dot in the earth's timeline. Read about Nyasasaurus, the oldest dinosaur so far, at Real Clear Science.
(Image credit: KDS444)
