Dinosaur evolutionary ancestors
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Dinosaur Evolutionary Ancestors: Early Archosaur and Dinosauromorph Origins
The evolutionary ancestors of dinosaurs trace back to a group of reptiles known as archosaurs, which also gave rise to crocodiles and pterosaurs. The closest relatives to true dinosaurs are the dinosauromorphs, a lineage that includes forms like Marasuchus, Lagerpeton, and silesaurids, which lived during the Middle to Late Triassic period 236.
Triassic Origins and Early Diversification of Dinosaurs
Fossil evidence places the earliest unequivocal dinosaurs in the Late Triassic (about 230 million years ago), with key discoveries from South America, particularly Argentina and Brazil. These early dinosaurs include Herrerasaurus, Eoraptor, Pisanosaurus, Saturnalia, and Staurikosaurus 249. However, trace fossils such as footprints suggest that the dinosaur stem lineage (Dinosauromorpha) originated even earlier, in the Early Triassic, shortly after the Permian-Triassic mass extinction, indicating a more gradual and extended rise of dinosaurs than previously thought .
Phylogenetic Relationships and Basal Dinosaur Groups
The relationships among the earliest dinosaurs and their close relatives remain debated. Traditional classification divides dinosaurs into two main groups: Saurischia (including theropods and sauropodomorphs) and Ornithischia. Recent studies propose alternative relationships, such as grouping Ornithischia and Theropoda together in a clade called Ornithoscelida, with Sauropodomorpha and Herrerasauridae as a separate branch 45. Silesaurids, once considered close relatives, may actually be early-diverging ornithischians, helping to explain gaps in the fossil record 14.
Ancestral Dinosaur Traits: Body Size, Locomotion, and Diet
Early dinosaurs and their immediate ancestors were generally small, bipedal animals. Fossils like Eoraptor and the tiny Kongonaphon from Madagascar show that miniaturization occurred near the base of the dinosaur and pterosaur lineages, possibly linked to ecological shifts such as insectivory and the origins of flight in pterosaurs 69. The earliest dinosaurs were likely carnivorous or omnivorous, with adaptations for an erect, bipedal gait—a key feature that may have contributed to their evolutionary success 29.
Geographic and Environmental Context of Dinosaur Origins
Most evidence points to a low-latitude, Gondwanan origin for dinosaurs, particularly in what is now South America and Africa. This region was part of the supercontinent Pangaea during the Triassic, allowing early dinosaurs and their relatives to disperse widely as they diversified 12. The apparent absence of early dinosaur fossils in other regions may be due to uneven sampling and preservation rather than true absence 16.
Conclusion
Dinosaurs evolved from small, bipedal archosaurian ancestors in the aftermath of the Permian-Triassic extinction, with their closest relatives being other dinosauromorphs like silesaurids and lagerpetids. Their early evolution involved significant miniaturization, ecological innovation, and rapid diversification, primarily in low-latitude regions of Gondwana. Ongoing discoveries and new phylogenetic analyses continue to refine our understanding of these remarkable evolutionary ancestors 1234569.
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