Tiny Fossil Discovered in Wyoming Reveals Great-Granddaddy of Hummingbirds

A petite and exquisitely preserved 50-million-year old fossil reveals the remains of a lustrous black bird that was the precursor to today's hummingbirds, researchers say.

The fossil bird, originally excavated from Wyoming's Green River Formation, is a new species to science, dubbed Eocypselus rowei. And though just 12 centimeters long, it was so well preserved that the impressions of its wing feathers could be studied in fine detail.

E. rowei (Credit: Lance Grande, Field Museum of Natural History)

This gave researchers at Chicago's Field Museum, where the fossil was found languishing in a collection, a lot to work with.

While many bird fossils feature only bones, E. rowei's nicely defined feathers allowed scientists to study its true size and proportions, providing a better sense of where the new bird might fit in the ornithological family tree.

After comparing the remains with many living and extinct species, they theorized that E. rowei was most likely the predecessor to the order of birds that today includes hummingbirds and swifts.

Although swifts and hummers may not seem like they have much in common, they do share traits that betray a shared evolutionary heritage. They're both small and migratory and eat insects, and perhaps most notably, they have legs so small as to be functionally useless, at least on the ground. Indeed, the order these birds comprise, called Apodiformes, means "having no feet." 

Ruby-throated hummingbird

Still, to most backyard observers, there are obvious differences between the two, especially in flight: Swifts are fast, daring flyers with long, tapered wings, while hummingbirds are known for hovering and darting, using disproportionately short wings.

What was striking to the scientists about E. rowei is that it seemed to have traits of both. It shared their tiny size and appetite for insects, but its wings were too small for the swift's rapid flight, but also too long to hover like a hummer.

Common swift (Credit: Paweł Kuźniar)

"This fossil bird represents the closest we've gotten to the point where swifts and hummingbirds went their separate ways," said lead researcher Daniel Ksepka of the National Evolutionary Synthesis Center, in a statement.

To round out our picture of E. rowei, the team was even able to study its feathers with an electron microscope, and discovered fossilized, carbon-rich pigment structures -- suggesting that, in life, it sported the iridescent black sheen found on swifts and other birds today.

The team published its findings in the Proceedings of the Royal Society B.