The Amazon delta was a tenth the size of a recently discovered dinosaur-era delta Planet Observer/Universal Images Group via Getty Images

A vast floodplain 10 times the size of the Amazon delta existed during the early days of the dinosaurs. It is the largest known delta from Earth’s history and may have been a crucial habitat.

During the Triassic period when dinosaurs first appeared, all of Earth’s continents were joined together in a supercontinent called Pangaea.

Part of northern Pangaea is preserved under the Barents Sea between Norway and Russia. Tore Grane Klausen, whilst at the University of Bergen in Norway, and his colleagues took data from wells drilled in the sea bed and combined this with seismic data to map the rock layers.


The team found preserved sediments from a delta that existed 237 to 227 million years ago. A delta is a wide, flat plain of muddy sediment that forms when a river meets a larger body of water, like a lake or ocean.

The remains span the entire Barents Sea and are 10 times the size of today’s largest deltas, in the Amazon and the Ganges. This equates to 1.65 million square kilometres, or about 1 per cent of the land area of modern Earth.

The team hasn’t officially named the discovery, but has informally called it the Snadd delta because it was found in rocks called the Snadd formation.

Delta plain dinosaur stomp

A delta forms when rivers carry sediments downstream then dump them by the coast. The accumulated sediments form vast, fertile plains that can support huge numbers of plants and animals.

The ancient delta was on the north coast of Pangaea. It was fed by multiple rivers, formed by intense monsoon rains, flowing north from a mountain range, which contained huge volumes of sediment.

The animals that would have lived in the delta haven’t been studied in detail, but they included amphibians called labyrinthodonts that often lived in wetlands. The plant life included lots of ferns and some conifers.

“Everywhere you look, you can pick up these sandstone samples with imprints of ferns,” says Klausen. Just off the coast, crocodile-like pliosaurs and dolphin-like ichthyosaurs ruled the seas.

Much of the rest of Pangaea was less hospitable. The regions close to the equator spent much of the Triassic as extremely hot and dry deserts, so the delta may have been a major centre of biodiversity.

This ancient flood plain was also long-lived, steadily growing for periods of 2 to 5 million years at a time. This suggests sea level didn’t change much, in line with the established idea that the Triassic had a steady “greenhouse” climate with little or no ice at the poles.

Journal reference: Geology, DOI: 10.1130/G45507.1