For a long time, the origin of dinosaurs remained one of paleontology’s biggest mysteries. That began to change in 1993 with the discovery of Eoraptor lunensis in Argentina’s Ischigualasto Formation—one of the earliest known dinosaurs, dating back about 231 million years. Scientists still debate whether Eoraptor was a primitive theropod or a more general saurischian, but either way, it marked a turning point in understanding how dinosaurs first evolved. Now, over 30 years later, that story conti