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On U-M Gateway: From obscurity to dominance: tracking the rapid evolutionary rise of ray-finned fish

7/22/2013

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Styracopterus, a later relative of Fouldenia that appeared alongside a host of fish with new body forms about 338 million years ago, is shown at a near-shore reef not far from the site where the Fouldenia fossils were collected. Painting credit: John Megahan.Mass extinctions, like lotteries, result in a multitude of losers and a few lucky winners. This is the story of one of the winners, a small, shell-crushing predatory fish called Fouldenia, which first appears in the fossil record a mere 11 million years after an extinction that wiped out more than 90 percent of the planet's vertebrate species.

The extinction that ended the Devonian Era 359 million years ago created opportunities quickly exploited by a formerly rare and unremarkable group of fish that went on to become—in terms of the sheer number of species—the most successful vertebrates (backboned animals) on the planet today: the ray-finned fish.

A University of Michigan evolutionary biologist and a colleague have shown that the previously known but misclassified Fouldenia was the first recorded shell-crushing ray-finned fish. This long-extinct fish, and a handful of its relatives, demonstrate that in the immediate aftermath of the end-Devonian extinction, ray-finned fish had already acquired a diversity of forms that gave them an evolutionary edge, enabling them to fill the ecological vacuum left by the demise of most major fish groups.

"This event 359 million years ago is called the Hangenberg extinction, and it nearly wiped out vertebrate life, which at the time was limited to the water," said Lauren Sallan, an assistant professor in the U-M Department of Ecology and Evolutionary Biology. "The ray-finned fish come to the fore after that event. They not only recover from this extinction, but they go from being a few minor lineages to dominating all the oceans."

A study by Sallan and Coates was published online July 22 in the Zoological Journal of the Linnean Society.

Caption: Styracopterus, a later relative of Fouldenia that appeared alongside a host of fish with new body forms about 338 million years ago, is shown at a near-shore reef not far from the site where the Fouldenia fossils were collected. Painting credit: John Megahan.