The earliest known dinosaur is Nyasasaurus parringtoni, which lived during the Middle Triassic period, around 243 million years ago. Discovered in Tanzania, Nyasasaurus represents a key transitional form, showcasing features that are both dinosaurian and pre-dinosaurian, highlighting the evolutionary path leading to more well-known dinosaurs of the Late Triassic and beyond. This discovery pushes back the origin of dinosaurs by approximately 10 to 15 million years earlier than previously thought, providing crucial insights into the early evolution of these remarkable creatures.

• Kingdom: Animalia > Phylum: Chordata > Class: Reptilia > Saurischia (or Ornithischia)
  (Clade: Dinosauria)

One of the earliest known true dinosaurs in the Dinosauria order is Eoraptor lunensis. From this predatory bird-like precursor, the birds and dinosaurs emerged. This direct-line ancestor evolved into theropods, birds, sauropods and ornithischians.

Eoraptor emerged during the Late Triassic period, approximately 231.4 million years ago, in what is now Argentina. It is considered one of the earliest and most primitive dinosaurs, exhibiting key dinosaur characteristics such as upright posture, bipedal locomotion, and a predatory lifestyle. Eoraptor belongs to the clade Saurischia and is classified within the family Eoraptoridae.