Dinosaurs originated roughly 10 million years before their oldest confirmed fossils, according to a new study. Published in Proceedings of the Royal Society B, the research estimates that these animals first appeared between 250 and 240 million years ago. That is significantly earlier than what the fossil record currently shows.
Chase Doran Brownstein of Yale University’s Ecology and Evolutionary Biology department led the study. His team analyzed nine separate fossil datasets using Bayesian tip-dating, a method that estimates when ancient lineages diverged by combining fossil data with models of how physical traits change over time.
The oldest confirmed dinosaur fossils date to around 230 million years ago. But the study found that all major dinosaur groups branched off within just five million years of their common ancestor.
Those groups include the plant-eating Sauropodomorpha, the bird-line Theropoda, the Ornithischia, and the predatory Herrerasauria. That pattern of fast, broad diversification from a single ancestor is the hallmark of what scientists call an evolutionary radiation.
Dinosaurs originated far earlier than the fossil record shows
Physical change among early dinosaurs was equally rapid. Rates of anatomical evolution peaked around 233 million years ago, coinciding with a climatic event known as the Carnian Pluvial Episode.
This period of heavy rainfall temporarily broke down arid barriers across the ancient supercontinent Pangaea, which had previously restricted where dinosaurs could spread.
Brownstein noted that this rapid divergence also explains a longstanding frustration in paleontology. When many species branch off quickly from a shared ancestor, they retain very similar physical features.
That similarity makes it extremely difficult to determine which groups are most closely related, and it has complicated early dinosaur family trees for decades.
Rapid early diversification left scientists with incomplete family trees
The study also found that dinosaur diversification did not end with the Triassic period. Successive mass extinctions repeatedly triggered new bursts of rapid evolution throughout the 240-million-year history of the group.
The mass extinction at the end of the Permian period, about 252 million years ago, appears to have created the ecological openings that first made the dinosaur radiation possible.
The researchers found no evidence that dinosaurs simply outcompeted other animals to achieve dominance. Instead, the pattern more closely resembles opportunistic diversification into vacant ecological roles. This mirrors how cichlid fish rapidly filled niches in African rift lakes without necessarily driving out competing species.
The study predicts that Early and Middle Triassic fossil sites in southern Pangaea hold the best chance of confirming an earlier dinosaur origin. Those fossils, the researchers note, have simply not been found yet.
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