Fossil analysis suggests the rise of creatures that could swim was gradual, not sudden
About 540 million years ago, the oceans were an alien landscape, devoid of swimming, or nektonic, creatures. Some scientists have hypothesized, based on fossil evidence, that swimmers suddenly dominated in the oceans during the Devonian Period, between 419 million and 359 million years ago. But an in-depth study of marine fossils now suggests that this so-called Devonian Nekton Revolution never actually took place.
Christopher Whalen and Derek Briggs, both paleontologists at Yale University, examined nearly 2,000 different genera of marine fossils dating to the Paleozoic Era, a vast span of geologic time between 540 million and 252 million years ago. Based on the creatures’ shapes, or morphologies, the researchers assessed whether the animals swam, and if they stayed close to the seafloor or ventured higher up in the water column.
The analysis showed no sudden burst of swimmers