Mammals, birds, fishes have won evolutionary race

August 24th, 2009 - 2:17 pm ICT by IANS  

Washington, Aug 24 (IANS) Mammals, birds and fishes are among evolution’s “winners” because they have diversified into more species, while crocodiles, alligators and their reptile cousin tuatara are among the “losers”, says a new study.
“Our results indicate that mammals are special,” said Michael Alfaro, University of California-Los Angeles (UCLA) assistant professor of ecology and evolutionary biology, who led the study.

Alfaro and colleagues analysed DNA sequences and fossils from 47 vertebrate groups and used a computational approach to calculate whether the “species richness” of each group was exceptionally high or low.

The research allows scientists to calculate for the first time which animal lineages have exceptional rates of success.

Among the evolutionary winners are most modern birds, including the songbirds, parrots, doves, eagles, hummingbirds and pigeons; a group that includes most mammals; and a group of fish that includes most of the fish that live on coral reefs, said Alfaro, an evolutionary biologist.

A group with the scientific name Boreoeutheria, which consists of many mammals, has diversified about seven times faster than scientists would have expected, beginning about 110 million years ago, Alfaro and his colleagues calculated.

The group includes primates and carnivores, as well as bats and rodents. Pouched mammals, such as kangaroos, are not as richly varied as other mammals, Alfaro said.

Modern birds have diversified about nine times faster than expected, starting about 103 million years ago, and the fishes that live on coral reefs have diversified about eight times faster than expected, he said.

Crocodiles and alligators are nearly 250 million years old yet have diversified into only 23 species, Alfaro said.

They are diversifying a staggering 1,000 times slower than would have been expected. “Their species richness is so low, given how old they are,” he said.

The tuatara, which lives in New Zealand and resembles lizards — although it is actually a distant cousin — has only two species.

“In the same period of time that produced more than 8,000 species of snakes and lizards, there were only two species of tuatara,” Alfaro said.

“That is one of the big mysteries about biodiversity,” Alfaro said. “Why these evolutionary losers are still around is a very hard thing to explain,” he said, according to an UCLA release.

Conversely, there are more than 9,000 bird species, more than 5,400 mammal species, approximately 5,500 frog species, some 3,000 snake species and 5,200 lizard species, Alfaro said.

The study, which also shows that new species emerge nearly as often as they die off, was published in the early online edition of Proceedings of the National Academy of Sciences.

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