Modern birds may have evolved before the mass extinction of the dinosaurs some 65 million years ago, the event conventionally believed to have shaped animal diversity today, a study says.

The first recognizable bird appeared during the Jurassic period about 150 million years ago, if the landmark fossil called Archaeopteryx -- a descendant of dinosaurs that grew feathers and took to flight -- is a guide.

During the subsequent Cretaceous period, birds developed widely, establishing major lineages.

But many experts believe that it took the extinction of the dinosaurs - wiped out by climate change triggered by the impact of a giant asteroid or comet - before birds, like mammals, were able to evolve into the extraordinarily diverse class and shapes they are today.

This "big bang" was facilitated mainly because the surviving species from the mass extinction were able to exploit habitat niches vacated by the dinosaurs.

That theory is now contested by the discovery of a fossil in Antarctica by paleontologists from Argentina and the United States.

The partial skeleton, found on Vega Island, western Antarctica, in 1992, is clearly a waterfowl and is "most closely related to Anatidae," a bird classification which includes modern ducks, they say.

That requires a rethink of the "big bang" bird theory, for it implies that the forerunners of modern ducks, chickens, ostriches and emus were around during the Cretaceous, authors say in a study published last Thursday in Nature, the weekly British journal.

"At least duck, chicken and ratite bird relatives were co-extant with non-avian dinosaurs," the authors believe.

The find has been baptized Vegavis iaii. The first word is an amalgam of Vega and avis, the Latin for bird, while iaii is taken from the initials for the Argentine Antarctica Institute (IAA) whose members collected the specimen.

The team was led by Julia Clarke of North Carolina State University

(China Daily January 25, 2005)