May 1, 2013
New Fossil Helps Explain Evolution Of Hummingbird Flight
Brett Smith for redOrbit.com - Your Universe Online
According to a recently published study in“¯Proceedings of the Royal Society B, a small bird fossil found in Wyoming could be the link that connects the evolutionary dots between hummingbirds and swifts.
"This fossil bird represents the closest we've gotten to the point where swifts and hummingbirds went their separate ways," said lead author Daniel Ksepka of the Field Museum of Natural History in Chicago.
The newly discovered bird was less than five inches long, weighed less than an ounce, and was named“¯Eocypselus rowei, after the Chairman of the Field Museum's Board of Trustees, John W. Rowe. Using radiometric dating, the team was able to determine that the bird lived about 50 million years ago — just after the age of the dinosaurs.
To determine the bird´s place in evolutionary history, the team compared the specimen to both extinct and contemporary species. Based largely on the analysis of its fossilized wing structure, the authors of the study concluded that the bird was an evolutionary precursor to Apodiformes, a class of birds that includes swifts and hummingbirds.
The unique wing shapes of swifts and hummingbirds have long puzzled scientists. In the new study, the authors noted that their new specimen could be the key to unlocking the history of these classes of birds. According to the authors, the wing shape and phylogenic position of E. rowei “support the inference that the shortened wings of hummingbirds and the elongated wings of swifts were each derived from a less specialized ancestral wing shape.”
Hummingbirds´ relatively short wings make them experts at hovering in mid-air, while the relatively long wings of swifts enables high-speed flight and easy gliding. However, the wing length of“¯E. rowei were somewhere in between.
"[Based on its wing shape] it probably wasn't a hoverer, like a hummingbird, and it probably wasn't as efficient at fast flight as a swift," Ksepka explained.
The shape of E. rowei´s wings, coupled with its petite size, imply that the ancestors of modern swifts and hummingbirds became smaller before each group's unique flight technique evolved.
"Hummingbirds came from small-bodied ancestors, but the ability to hover didn't come to be until later," said Ksepka.
Using a scanning electron microscope, the researchers found that carbon residues in the fossils are fossilized melanosomes, tiny pigment-holding cell structures that give birds and other animals their color. Based on an analysis of these melanosomes, the researchers said E. rowei was probably black and may have had a glossy sheen, like modern swifts. They added that the ancient bird probably ate insects based on the shape of its beak.
In their conclusion, the study authors noted that the new species “offers a glimpse into the early evolution of one of the most diverse and ecologically important” classes of birds. However, they also noted that more fossil evidence needs be recovered for a more complete picture of their evolution.