Fossil illuminates ancestry of swifts and hummingbirds

Diminutive size came before specialized wings

Two aerial acrobats with very different flying styles probably shared a much less agile common ancestor, a spectacularly preserved bird fossil reveals.

Today’s swifts fly fast and glide gracefully thanks to their lanky, long wings, while their hummingbird relatives use short, bladelike wings to hover. It’s unclear how and when these wing shapes emerged. Feathers can offer crucial hints, but they’re usually poorly preserved in fossils.

Luckily, the feathers of a fossil unearthed recently in Wyoming are so well preserved that microscopic features are visible, says Daniel Ksepka of North Carolina State University, who led a team that analyzed the fossil.

To assess the 52-million-year-old specimen’s place in avian history, the researchers compared anatomical features of the fossil — Eocypselus rowei — to those of other extinct and modern species. 

An ancient relative of short-winged hummingbirds and long-winged swifts had medium-length wings and a tiny body, researchers surmise based on a new fossil (shown) with well-preserved feathers. Lance Grande/Field Museum of Natural History

The ancient species likely split off from a lineage that spawned hummingbirds and swifts, the researchers found.

E. rowei’s wings were smaller than swifts’ but larger than hummingbirds’, suggesting the ancient creature couldn’t glide or hover well. And this bird was just 12 centimeters long — similar in size to many of today’s swifts and large hummingbirds, and probably smaller than its own predecessors, Ksepka says. The common ancestors of hummingbirds and swifts likely became smaller first. Then the lineage split into two groups and the birds’ wings developed their distinctive forms, the researchers report May 1 in Proceedings of the Royal Society B.

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