Mass extinction of ancient fish may have led to humans

LOS ANGELES - Modern-day lizards, snakes, frogs and mammals - including us - may owe their existence to a mass extinction of ancient fish 360 million years ago that left the oceans relatively barren, providing room for marginal species that were our ancestors to thrive and diversify, paleontologists proposed yesterday.

The report, by University of Chicago researchers, focused on events at the end of what is commonly called the Age of Fishes, which lasted from 416 million years ago to 359 million years ago. That age was followed by a 15-million-year period of relative silence in the fossil record.

Paleontologists had tended to ignore the rarity of fossils from that period, known as Romer's gap - assuming that they just had not been found or shrugging it off as a period of low diversity.

But in a paper published online yesterday in Proceedings of the National Academy of Sciences, the authors proposed that Romer's gap is really a sign that the world's marine vertebrates were recovering from a global-scale extinction event.

That gap left ocean niches bereft of weird, now-extinct fishes like the giant armor-plated Dunkleosteus that had ruled the seas up till then, permitting then-marginal species such as sharks to gain ascendancy, scientists said.

"Forty-four percent of all vertebrate life went extinct at that point, and that was not recognized before," said John Long of the Natural History Museum of Los Angeles County, who was not involved in the study.

It was one of the most devastating events in Earth's history, on a par with the one that killed off the dinosaurs 65 million years ago, said Lauren Sallan, a University of Chicago paleontologist, the paper's lead author.

This extinction of fish made way for modern marine life such as sharks and the ancestors of modern fish, she said.