Ray-finned fishes get new family tree

By Natalia Real
August 8, 2012

A genetic analysis by Yale University researchers shows that the earliest ray-finned fishes called teleosts are more ancient than originally thought and emerged on Earth almost 300 million years ago. The much more diverse and familiar species of teleosts, however, arose at about the same time as birds and mammals: about 120 to 60 million years ago.

This means that the most common lineages of fish found today in oceans, lakes and rivers evolved at about the same time as mammals and birds did. The analysis was reported this week in the Proceedings of the National Academy of Sciences.

The comparative genetic analysis of more than 200 fish species gave an earlier than expected evolutionary birthday to well-known ray-finned fish such as salmon, bass or tuna. It also demonstrates that the very earliest lineages of living teleost fish were eels and bonefishes, as opposed to tropical freshwater bonytongue fish, which is what some scientists had postulated.

“Half of all animals that have backbones are ray-finned fish, but we know little about their evolutionary history in contrast to other vertebrate lineages like frogs, lizards, birds, and mammals,” said Thomas Near of the Department of Ecology and Evolutionary Biology at Yale and lead author of the paper. “Fish are usually viewed as primitive in origin, but we are learning that most of the familiar living lineages of fish arose more recently — during what we might call the Second Age of Fishes.”

The Devonian period, which occurred 415 to 355 million years ago, is known as the Age of Fishes and heralded the appearance of many types of fish — such as bony fishes, sharks, skates and rays — as well as lineages known only from the fossil record. The living lineages of teleost fish, which is the major group of ray-finned fish, were thought to have first appeared some 150 million years ago, instead of 300 million years ago, as the Yale study suggests.

Still, the analysis shows that most teleost lineages found in the present day appeared much later — in the Cretaceous through the Paleocene, some 120 to 60 million years ago, along with the first mammals and birds. The team is investigating whether the dinosaur extinction event some 65 million years ago also may have helped teleost fishes spread out throughout the world’s oceans and rivers, just as it did with mammals and birds.

“The new family tree of ray-finned fish comes close to completing the book on the evolutionary relationships of vertebrates,” Near said.

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