Underwater Canyons Preserved Earth’s Oldest Animals, Study Finds

Soft bodies rarely fossilize. ScienceAlert reported that the team wanted to know how the Flinders Ranges came to hold such a rich and diverse record from a period that lasted from about 635 million to 538.8 million years ago.

What the mapping showed

The researchers mapped geological features across the mountain range to reconstruct the terrain of about 550 million years ago. They found traces of colossal canyons running southeast. In places they plunged to depths of 280 meters (919 feet) and stretched more than 6 kilometers (3.7 miles) across.

The canyons seem to have formed largely through erosion under the sea, after a major fall in sea level. When the sea rose again, the land flooded and the canyons filled with sediment.

In those conditions, a layer of Rawnsley Quartzite called the Ediacara Member preserved rare clues about the region's inhabitants. Sediment deposits in the canyons point to powerful water flows that could have moved large volumes of material. Drawing on modern submarine canyons, the researchers conclude that underwater erosion is more likely to have driven this than river action alone.

"We found evidence that huge underwater canyons cut across the continental shelf before being rapidly flooded as sea levels rose again," Faehnrich said. He added that the flooding "created the conditions that allowed one of the world's richest Ediacaran fossils to be preserved."

Open questions

The study does not settle where the Ediacaran biota sit on the animal family tree. It is unclear whether they were ancestors of later animals or evolutionary dead ends. Nor is it known why they diversified so quickly and then declined.

Earlier research linked the biota to global sea-level changes, which have been cited both as a driver of evolutionary innovation and as a factor in fossil preservation. That link is speculative, and the role of sea level in the creatures' fortunes is still unknown.

Co-author Diego Garcia-Bellido, a biologist, said: "The evidence points to a combination of changing sea levels and local geological processes shaping the ancient basin."