“Dawn swift” illuminates origins of swifts and hummingbirds

dawnswiftFrom the spectacular Green River Formation of Wyoming comes a tiny fossil that researchers have identified as a possible relative of both hummingbirds and swifts.

When Eocypselus rowei, whose genus name is Greek for “dawn swift,” died approximately 50 million years ago, it fell into shallow, oxygen-poor water and was covered with fine layers of mud that preserved minute details of its body and plumage. Except for its long wings, the fossil shows few hummingbird-like characteristics. Its stubby bill is more like those of swifts and suggests that, like them, it fed on flying insects. Though about the length of a Magnificent Hummingbird (12 cm, 4 3/4″), its short bill, proportionally larger skull, and longer wing and leg bones would have made it heavier. “Shadows” in the stone surrounding its bones are fossilized pigment structures that would likely have given it a glossy, possibly iridescent black color like many modern swifts.

Though hummingbird fossils have been found so far only in Europe, Eocypselus shows that possible distant hummingbird ancestors did occur in the Americas.

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Fossil evidence of wing shape in a stem relative of swifts and hummingbirds (Aves, Pan-Apodiformes)

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