Nyasasaurus could be the earliest known dinosaur, or else a close relative of early dinosaurs. (Credit: Mark Witton/The Trustees of the Natural History Museum, London)

LONDON — The mystery of dinosaur origins has taken an unexpected turn toward the equator. While paleontologists have long searched southern regions for clues about where these magnificent creatures first evolved, new research suggests we may have been looking in the wrong latitude altogether. A new study indicates that the first dinosaurs may have emerged in Earth’s ancient tropics, forcing scientists to reconsider long-held theories about their origins.

For years, paleontologists believed dinosaurs originated in what is now southern South America and southern Africa, since the oldest unequivocal dinosaur fossils come from late Carnian rock formations (around 230 million years ago) in these regions. However, these earliest assemblages already show remarkable diversity in both anatomy and species variety, hinting at an even earlier evolutionary history that remains undiscovered.

“Dinosaurs are well studied but we still don’t really know where they came from. The fossil record has such large gaps that it can’t be taken at face value,” explains lead author Joel Heath, a PhD student at University College London Earth Sciences and London’s Natural History Museum, in a statement.

The research team analyzed the distribution patterns of early dinosaurs and their close relatives using sophisticated computational models that account for gaps in fossil sampling across different regions. Their results, published in Current Biology, frequently support the emergence of dinosaurs in low-latitude regions of the ancient supercontinent Gondwana — essentially the tropical areas of what would become Africa and South America.

“Our modelling suggests that the earliest dinosaurs might have originated in western, low-latitude Gondwana. This is a hotter and drier environment than previously thought, made up of desert- and savannah-like areas,” says Heath.

During this early period, dinosaurs were far from dominant. They shared their world with various reptilian cousins, including pseudosuchians — an abundant group containing species up to 10 meters long that were ancestors to modern crocodiles — and pterosaurs, the first animals to achieve powered flight. While their descendants would later grow to enormous sizes, the earliest dinosaurs were relatively small, comparable to modern chickens or dogs, walked on two legs, and were likely omnivorous.

Most notably, the tropical origin hypothesis gained its strongest support when the researchers considered silesaurids (early dinosaur relatives) as primitive ornithischian dinosaurs. This placement helps explain a long-standing puzzle: why we don’t find any ornithischian dinosaur fossils before the Early Jurassic period, despite knowing the group must have existed earlier based on evolutionary relationships.

Modern tropical regions like northern Africa and the Amazon rainforest have yielded relatively few dinosaur fossils compared to temperate zones. “So far, no dinosaur fossils have been found in the regions of Africa and South America that once formed this part of Gondwana. However, this might be because researchers haven’t stumbled across the right rocks yet, due to a mix of inaccessibility and a relative lack of research efforts in these areas,” Heath explains.

The study indicates that the entire radiation of archosaurs likely occurred within low-latitude Gondwana following the devastating end-Permian mass extinction about 252 million years ago. From these tropical origins, different lineages then dispersed across Pangaea into various ecological and climatic zones during the Late Triassic period.

Professor Philip Mannion, senior author from UCL Earth Sciences, notes: “Our results suggest early dinosaurs may have been well adapted to hot and arid environments. Out of the three main dinosaur groups, one group, sauropods, which includes the Brontosaurus and the Diplodocus, seemed to retain their preference for a warm climate, keeping to Earth’s lower latitudes.”

Understanding dinosaur origins requires not only examining where their fossils have been found but also considering where they haven’t been found, and why. This study suggests that the next breakthrough in dinosaur evolution might come not from new fossil discoveries, but from better understanding the biases and gaps in our current knowledge.