New branches on the tree of life had sprouted, setting the stage for an explosive diversification of forms that evolutionary biologists call an adaptive radiation. These events often occur in response to new ecological opportunitieswhen habitats are unoccupied by competitors, for example. That's what happened when a much later extinction killed off the dinosaurs and allowed mammals to take over those reptiles' ecological roles.
Something similar happened to ray-finned fish, which have fins supported by long, bony rods arranged in a ray pattern. Before the extinction, fish were dominated by two groups: the armor-plated, predatory placoderms and the lobe-finned fish, whose fins are borne on a fleshy, scaly stalk extending from the body.
Placoderms were eliminated by the end-Devonian extinction, and most of the lobe-finned fish perished as well, though survivors live on today in the lungfish and the coelacanth. In addition to a few ray-finned fish, some sharks and tetrapods survived the Hangenberg event. Tetrapods later crawled ashore and evolved into amphibians, reptiles, birds and mammals.
Other survivors of the Hangenberg event included sea urchins, sea lilies and shelled invertebrates called brachiopods. With most other predators now out of the picture, early sharks and ray-finned fish like Fouldenia used their crushing jaws to dine on these spiny, stalked and hard-shelled creatures.
"Because the ecosystem's been decimated, the only thing left to prey on are shelly animals," Sallan said. "So in this vacuum left by the mass extinction event, a bunch of different animals are going into these vacated niches and taking over those jobs."
The Hangenberg event was the final blow in a series of mass extinctions that ended the Devonian, which is often called the Age of Fish. The Hangenberg extinction is
|Contact: Jim Erickson|
University of Michigan