A fresh look at forgotten fossils has revealed two new species of giant, filter-feeding fish that swam Earth’s oceans for 100 million years, occupying the ecological niche now filled by whales and whale sharks.

Until now, that ancient niche was thought to be empty, and such fish to be a short-lived evolutionary bust.

“We knew these animals existed, but thought they were only around for 20 million years,” said Matt Friedman, a University of Oxford paleobiologist. ”People assumed they weren’t important, that they were an evolutionary failure that was around for a brief time and winked out. Now we realize that they had a long and illustrious evolutionary history.”

In a paper Feb. 18 in Science, Friedman and five other paleobiologists describe Bonnerichthys gladius and Rhinconichthys taylori.

They belong to the pachycormid genus, an extinct group of immense fishes that ate by drifting slowly, mouth agape, sucking down plankton and other tiny aquatic life.

Prior to the paper’s publication, pachycormids were known from fossils of a single species, Leedsichthys problematicus. (The species name derives from the fragmented remains of its first fossils.)

Leedsichthys was an impressive creature, reaching lengths of 30 and perhaps even 50 feet, but its fossils have only been found in western Europe and are between 160 and 145 million years old — a brief, relatively unexceptional footnote to animal history.

However, during a chance visit by Friedman to the University of Kansas, researchers from their Natural History Museum told him of odd recoveries from a newly-prepared fossil deposit: delicate plates and long rods of bone, jumbled beyond recognition.

As Friedman put the pieces together, he realized that the plates were part of a jaw, and the rods were gills. That configuration was known from Leedsichthys, but this clearly belonged to a new species.

Working with other museums, Friedman found more examples of the species, which he dubbed B. gladius.

They had been collected in the 19th century and mistakenly classified as Leedsichthys, or dismissed as uninteresting. By the time he was finished, Friedman found B. gladius fossils as old as 172 million years, and as young as 66 million years.

In the dusty recesses of London’s Natural History Museum, He also found another pachycormid species, R. taylori; it had been mischaracterized and forgotten by Gideon Mantell, the English paleontologist credited with starting the scientific study of dinosaurs.

Altogether, the fossils showed that pachycormids were not a footnote, but an evolutionary chapter that spanned more than 100 million years.

Read the complete article at: wired.com