Did dinosaurs first roam the Amazon? New study offers clues

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.

equatorial regions of South America and Africa, including the Amazon, millions of years earlier than current fossil evidence shows.

This new research, led by University College London (UCL) and published in Current Biology, sheds light on a critical mystery in the story of dinosaurs.

The oldest known dinosaur fossils, like Eoraptor and Herrerasaurus, date back about 230 million years and have been found further south in areas such as Argentina, Brazil, and Zimbabwe.

However, the differences between these fossils indicate that dinosaurs were evolving long before these specimens appeared.

The study’s models suggest their origins may lie in an ancient part of the supercontinent Gondwana, which includes today’s Amazon, Congo Basin, and Sahara Desert.

Lead author Joel Heath, a Ph.D. student at UCL and the Natural History Museum in London, explained: “Dinosaurs are well-studied, but we still don’t fully understand where they came from.

The fossil record has large gaps, and much of it is missing, especially in places like equatorial Gondwana.”

The team’s research combined fossil data, evolutionary family trees of dinosaurs and their close relatives, and reconstructions of Earth’s geography during this time. They treated areas where no fossils have been found as gaps in research, rather than assuming these regions had no fossils at all.

The earliest dinosaurs were very different from the massive creatures we think of today. They were small—closer in size to a chicken or dog—and walked on two legs.

Most were likely omnivores, eating a mix of plants and small animals. During this time, dinosaurs were vastly outnumbered by other reptiles, including pseudosuchians (ancestors of crocodiles) and pterosaurs, the first animals capable of powered flight.

Dinosaurs only rose to dominance after a massive extinction event 201 million years ago, caused by volcanic eruptions that wiped out many of their reptile relatives.

The study’s models suggest early dinosaurs were well-suited to hot, arid environments like the deserts and savannas of equatorial Gondwana. These areas were a midpoint between the regions where the earliest dinosaur fossils have been found and areas in the northern supercontinent Laurasia, where fossils of their close relatives were discovered.

Interestingly, one group of dinosaurs—sauropods, which include Brontosaurus and Diplodocus—seemed to retain their preference for warm climates. The other two groups, theropods (like Tyrannosaurus rex) and ornithischians (like Triceratops), later developed the ability to generate body heat, allowing them to thrive in colder areas, even near the poles.

The researchers also found evidence that silesaurids, long thought to be cousins of dinosaurs, might actually be ancestors of ornithischians. This finding could help explain why ornithischians are missing from the fossil record of the earliest dinosaur era.

Senior author Professor Philip Mannion from UCL said, “Our findings suggest that dinosaurs were well adapted to life in harsh, hot environments. This might be the key to understanding how they first emerged and later spread across the world.”

Source: University College London.