Mass fish extinction paved way for modern vertebrates
Washington: A new study says that modern-day lizards, snakes, frogs and mammals - including humans - owe their existence to a mass extinction of fish 360 million years ago.
According to the study, the prehistoric fish extinction 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 that exist today.
"Everything was hit; the extinction was global. It reset vertebrate diversity in every single environment, both freshwater and marine, and created a completely different world," said Lauren Sallan of the University of Chicago and lead author of the paper.
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. Just about everything dominant in the Devonian died at the end of the period and was replaced," Sallan said.
Michael Coates, an organismal biologist and anatomist at the University of Chicago, the paper``s second author, said: "There``s some sort of pinch at the end of the Devonian."
"It``s as if the roles persist, but the players change: the cast is transformed dramatically. Something happened that almost wiped the slate clean, and, of the few stragglers that made it through, a handful then re-radiate spectacularly," he added.
The study has been published this week in the journal Proceedings of the National Academy of Sciences.
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