Sunday, 5 May 2013

On The Origin Of Hummingbirds

A silhouette of an emerald hummingbird I saw while in Ecuador 
Hummingbirds are extraordinarily beautiful creatures. Even the largest species is no bigger than a satuma. Yet they compact a complete set of organs and a pair of wings capable of beating hundreds of times a second; true miracles of evolutionary engineering.

They perform some of the most complex aerobatics of any animal in existence. They are able to hover, keeping their heads perfectly still while feeding from nectar-rich flowers with long, needle-thin beaks with a degree of precision comparable to keyhole surgery .

Their swift-beating wings, generate lift and move in a figure of eight pattern unique to the group. The wing thrust acts in both directions, so the overall motion forwards or backwards is virtually zero. This aerial ballet is so specialist that the origins of the creatures' powers of flight baffled palaeontologists for decades. Yet a fossil discovery from Wyoming by researchers working at the Field Museum of Natural History in Chicago offers a few clues. The specimen is beautiful and so well preserved that it looks like a painting against a background of speckled shale. While it is only 12 centimetres in length, every bone is present, with feathers consisting of reddish halos which fringe the skeleton.

The species, named Eocypselus rowei, after examination, showed that it was not in fact a hummingbird, but a precursor to the group. It has been a long-held fact that hummingbirds split from the swift family. 'This fossil bird represents the closest we've gotten to the point where swifts and hummingbirds went their separate ways,' said Daniel Ksepka from the National Evolutionary Synthesis Center in Durham, North Carolina.

The 50 million year old, beautifully preserved fossil of the hummingbird ancestor Eocypselus rowei from the Green River Formation in Wyoming,
A comparison of Eocypselus' wings with those found in members of the two descendant groups showed that it combined elements from both. Swifts have long wings designed for high speed flight and gliding. Hummingbirds have shorter wings designed for hovering and quick darting motions. As a result, we can see that Eocypselus would have been proficient in the air, yet was showing signs of the specialized structures needed for more complex methods of flight.

Of course, a small size is requisite to both groups, so it seems, based on the fossil's size, that the ancestors became small before their complicated means of flight began to develop. Due to its well preserved nature, the researchers were able also to extract information beyond flight. By studying preserved melanosomes within the feathers, they determined that Eocypselus would have been glossy black, similar to modern swifts, while an examination of its beak revealed that it was probably an insect eater.

Birds underwent an evolutionary radiation after the demise of the dinosaurs. The skies were no longer ruled by pterosaurs, dinosaurs no longer threatened their nests and mammals had yet to become either large or fearsome. The birds were able to flourish.  Some became predators in their environment, growing to over three metres tall with beaks built like cleavers. While others took an alternative route. These became diminutive, yet more complex, evolving ultimately into the hummingbird.