Author: Carolyn Gramling / Source: Science News
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 during the Devonian, the researchers contend July 18 in Proceedings of the Royal Society B. Instead, over time, “the water column was slowly filling with larger, more actively swimming animals,” Whalen says. “By the end of the Paleozoic, the oceans looked more like the oceans we know today.”
The Paleozoic got started with a bang with a burst of biodiversity famously known as the Cambrian explosion that brought into the world most of its modern major phyla, from arthropods to tardigrades. Some 40 million years later, the Great Ordovician Biodiversification Event added new branches to the tree of life, with cephalopods such as jellyfish and gastropods such as snails.
The Devonian Period was also an exciting time for life. It has been called both the age of fishes and the age of forests, as bony fishes and…
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