A mass extinction of fish 360 million years ago hit the reset button on Earth's life, setting the stage for modern vertebrate biodiversity. The mass extinction scrambled the species pool near the time at which the first vertebrates crawled from water towards land.
Those few species that survived the bottleneck were the evolutionary starting point for all vertebrates--including humans--that exist today, according to results of a study published this week in the journal Proceedings of the National Academy of Sciences (PNAS).
"Everything was hit; the extinction was global," said Lauren Sallan of the University of Chicago and lead author of the paper. "It reset vertebrate diversity in every single environment, both freshwater and marine, and created a completely different world."
The Devonian Period, which spanned from 416 to 359 million years ago, is also known as the Age of Fishes for the broad array of species present in Earth's aquatic environments.
Armored placoderms such as the gigantic Dunkleosteus and lobe-finned fishes--similar to the modern lungfish--dominated the waters, while ray-finned fishes, sharks and tetrapods were in the minority, according to Maureen Kearney, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research, along with NSF's Division of Earth Sciences.
But between the latest Devonian Period and the subsequent Carboniferous period, placoderms disappeared and ray-finned fishes rapidly replaced lobe-finned fishes as the dominant group, a demographic shift that persists to today.
"The Devonian period is known as the Age of Fishes, but it's the wrong kind of fish," Sallan said. "Just about everything dominant in the Devonian died at the end of the period and was replaced."
"There's some sort of pinch at the end of the Devonian," said the paper's second author, Michael Coates, an organismal biologist and
|Contact: Cheryl Dybas|
National Science Foundation