Prehistoric fish extinction cleared path for vertebrates
A mass extinction of prehistoric fish some 360 million years ago
cleared the path for the evolution of modern vertebrates, a study
published Monday has found.
“Everything was hit; the extinction was global,” said lead author
Lauren Sallan of the University of Chicago.
A prehistoric fish. Source: google |
“It reset vertebrate diversity in every single environment, both
freshwater and marine, and created a completely different world.”
While the mass extinction at the end of the Devonian period is among
the five most significant in the earth’s history, researchers are not
certain as to how it was triggered.
It is believed to have occurred in a series of events over the course
of 20 to 25 million years and accounted for the extinction of about 20
percent of all animal families and 70 to 80 percent of all animal
species.
There is evidence of substantial glacier formation during the period,
which would have dramatically lowered sea levels in the “Age of Fishes,”
and the first appearance of forests might also have produced
catastrophic atmospheric changes.
The armed placoderms and lobe-finned fish which dominated the
Devonian Period were replaced by ray-finned fish, in a demographic shift
that persists to this day.
“There’s some sort of pinch at the end of the Devonian,” said
co-author Michael Coates, a biologist and anatomist at the University of
Chicago.
“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.”
By analyzing the vertebrate fossil record, Sallan and Coates were
able to pinpoint a critical shift in diversity to the Hangenberg
extinction.
While the earliest four-limbed creatures, or tetrapods, made the
first tentative steps toward a land-dwelling existence prior to this
extinction event, there was a 15 million year stretch of the fossil
record almost barren of tetrapods.
“Something that’s seen after an extinction event is a gap in the
records of survivors,” Sallan said. “You have a very low diversity
fauna, because most things have been killed off.”
The limited number of tetrapods which survived the extinction were
likely the early ancestors of the vast majority of modern land
vertebrates, the authors speculated.
“Extinction events remove a huge amount of biodiversity,” Coates
said. “That shapes in a very significant way the patchiness of
biodiversity that persists to the present day.”
The study was published in the Proceedings of the National Academy of
Sciences.
AFP |