Fossils are the preserved remains or traces of ancient life, providing valuable clues about Earth’s past. Dinosaurs were a diverse group of reptiles that first appeared millions of years ago.
The Earliest Known Dinosaur
The dinosaur often considered the oldest known is Nyasasaurus parringtoni. It lived approximately 240-245 million years ago during the Middle Triassic period. Its remains were discovered in the Manda Formation of Tanzania, Africa. Though fragmentary, its fossils provide evidence of an early dinosauromorph, a group that includes dinosaurs and their closest relatives.
Other contenders for early dinosaurs or very close relatives include Herrerasaurus and Eoraptor. Herrerasaurus ischigualastensis, a carnivorous bipedal dinosaur, dates to about 231.4 million years ago and was found in the Ischigualasto Formation of Argentina. It is classified as an early saurischian, or “lizard-hipped,” dinosaur. Eoraptor lunensis, another small, early dinosaur, lived around 231 to 228 million years ago and was also found in the Ischigualasto Formation in Argentina. It is considered one of the earliest sauropodomorphs and was likely an omnivore.
Identifying Ancient Dinosaurs
Paleontologists identify dinosaur fossils by specific anatomical features that distinguish them from other reptile groups, such as crocodiles or pterosaurs. One characteristic is their upright posture, where hind limbs are held directly beneath the body, similar to most mammals. This differs from most other reptiles, whose limbs sprawl out to the sides.
This upright stance is made possible by a unique hip structure. Dinosaurs possess a “perforate acetabulum,” a hip socket with a hole in the center where the head of the thigh bone (femur) inserts. This open hip socket allows the leg to move freely directly under the body. Other features include a sacrum (the part of the vertebral column attached to the pelvis) composed of three or more fused vertebrae, and modifications to the skull and limb bones.
Unlocking Dinosaur Origins
The discovery of these dinosaur fossils provides insights into their initial evolution and diversification. Early dinosaurs were often small, bipedal, and carnivorous or omnivorous, adapting to various environments across the supercontinent Pangea. Their emergence in the Triassic period, roughly 252 to 201 million years ago, allowed for their eventual rise.
These early finds show that dinosaurs gradually diversified, occupying ecological niches that became available after major extinction events. For example, the Triassic-Jurassic extinction event, around 201.3 million years ago, wiped out many competing archosaurs and allowed dinosaurs to become the dominant terrestrial vertebrates. Studying these early forms helps scientists understand how dinosaurs developed adaptations that allowed them to thrive and grow to immense sizes in later geological periods.
The Ongoing Quest for Early Life
The title of “oldest dinosaur fossil” is not static; it can change as new discoveries are made and scientific understanding evolves. The precise classification of some early fossils as definitive dinosaurs versus their close relatives, known as dinosauromorphs, is an ongoing area of research.
Other early finds include dinosauromorphs like Lagerpeton and Marasuchus, considered very close relatives to dinosaurs. These non-dinosaurian dinosauromorphs coexisted with early dinosaurs for millions of years. Each new fossil discovery, whether of a dinosaur or a closely related ancestor, contributes to a more complete picture of how these creatures first appeared and diversified on Earth.