Washington, Aug 24 - 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.