For several decades, scientists have placed polypterids down near the base of the family tree of ray-finned fish, a large group believed to have originated around 385 million years ago.
But a new study that used CT scans to probe three-dimensionally preserved fossil fish skulls shakes up the fish family tree by concluding that the emergence of polypterids occurred much later than researchers had thought. The findings also suggest that the origin of all modern ray-finned fish may have occurred tens of millions of years later than is generally believed.
Ray-finned fish represent about half of all backboned animals on Earth. For every species of mammal, bird, reptile and amphibian on land, there is a species of bony fish in the ocean.
“While this finding extends the fossil record of polypterids, it also has some unexpected consequences,” U-M’s Friedman said. “It shows that many features of polypterids aren’t primitive at all, but rather are specializations that evolved later in their history.”
Said Oxford’s Giles: “Polypterids appear to have undergone several reversals in their evolution, which has clouded the view of their position in the fish family tree. It’s like if your brand new smart phone came with a rotary dialer and without Wi-Fi. We know it’s the latest handset, but its characteristics might lead us to thinking it’s an older model.”
This repositioning of the polypterids sends shock waves through the fish family tree and suggests that ray-finned fish may have emerged tens of millions of years later than scientists had thought, near the boundary between the Devonian and Carboniferous periods about 360 million years ago. Paper. (paywall) – Sam Giles, Guang-Hui Xu, Thomas J. Near, Matt Friedman. Early members of ‘living fossil’ lineage imply later origin of modern ray-finned fishes. Nature, 2017; DOI: 10.1038/nature23654More.
Which mean that they evolved quickly later than thought rather than evolving quickly earlier than thought—and sometimes reversed in evolution. Not a simple story.
Note: Posting light till late tonight due to O’Leary for News’s other alternate day job.
See also: Humans split from apes later than thought?