Saturday, 6 June 2015

A Remarkable New Species Of Fossil Avian

Over 10,000 species strong, the bird family is incredibly diverse. From the small and drab to the flamboyant and brightly coloured, the number of different forms is bewildering. The bird family has undergone a sudden evolutionary radiation during the last 65 million years of planetary history. The demise of the dinosaurs opened up a multitude of ecological niches which they quickly exploited. Some became giant, flightless predators. Others took to the skies. While many took a the third way, eking out an existence in the trees.

Hummingbirds and birds-of-paradise are perhaps the most beautiful examples. They are recent groups, having evolved in the last 65 million years. Yet birds with bright colours and complex plumage did exist during the time of the dinosaurs. One such species has been recently discovered.

Unusually it came not from China, where so many Mesozoic avians have been located, but Brazil. At 115 million years old, the specimen was collected in 2011 from mid Cretaceous rocks in the Araripe Basin. The locality has yielded hundreds of fossil species, including plants, insects, fish, turtles and flying reptiles. This bird adds to its biological diversity.

The fossil enantiornithine which clearly displays two long tail feathers
Yet its importance lies with its remarkable tail feathers. The two flat, ribbon-like plumes were longer than the body itself. These were certainly not aerodynamic structures but were almost certainly brightly coloured and part of some kind of mating display or used as a means of communication. Intriguingly the bones were not fully developed and the eyes were exceptionally large for the body, indicating that this creature was a juvenile. This provides interesting material regarding the study of sexual maturity versus physical maturity in extinct species.

An artist's impression of the 115 million year old enantiornithine from Brazil
Equally intriguing is its classification. While it has yet to be assigned a species and genus, its morphology indicates that it was part of a now extinct group of avians known as the enantiornithes.

During the Cretaceous, Earth's landmasses were grouped together into two super-continents: the southern Gondwana and the northern Laurasia. Previously all enantiornithine fossils came from Laurasia. This new species, however, would have inhabited Gondwana. This indicates that the group was global.

'We would have figured it out from the few fossils here and there, but this is really a great find. It's a whole new continent where enantiornithes were probably flying about,' said Richard Prum, a professor of ornithology at Yale University.

In bird evolution, the enantiornithine family came after the most primitive birds - creatures like Archaeopteryx and Confuciusornis. What their geographical location suggests is that birds underwent a rapid diversification during the Cretaceous, spreading from their ancestral homeland of Laurasia to Gondwana. Why has yet to be established, but a possible reason is the spread of forests after the decline of then giant Jurassic sauropod grazers. Large forested environments would have been prime centres for early birds to evolve and diversify, as their descendants would do in the last 65 million years with the recovery of the forests after the K-T boundary extinction.