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Ancient WorldsAncient Worlds

New fossil find complicates the meandering story of dinosaur flight

A chicken-sized raptor relative adds credence to the idea that flight evolved multiple times among ground-faring dinosaurs.

ByKatherine J. WuNOVA NextNOVA Next
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An artist's impression of a pair of Hesperornithoides miessleri, which, despite being flightless, had many bird-like features, including feathered forelimbs. Image Credit: Illustration by Gabriel Ugueto

A new chicken-sized dinosaur might be adding a twist to the origin story of flight.

Reporting yesterday in the journal PeerJ, a team of paleontologists announced the debut of Hesperornithoides miessleri, a ground-dwelling raptor relative unearthed from a 150-million-year-old rock formation in Wyoming in 2001.

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The species is so far represented by a single specimen nicknamed “Lori,” but this petite predator could occupy a unique place in evolutionary history. Hesperornithoides was almost certainly a flightless runner. But its placement in time and space may hint that this mode of locomotion was also a feature in the precursors of modern birds, the researchers argue. This would suggest that a line of terrestrial—rather than arboreal—dinosaurs were first in flight.

Regardless of where Lori’s lineage ultimately led, though, the specimen is still notable for several reasons. With a body like a chicken with a two-foot-long tail, Hesperornithoides is the smallest dinosaur discovered so far in Wyoming, where paleontologists have uncovered giants like Stegosaurus and Allosaurus in the past.

Hesperornithoides is also now North America’s oldest known raptor-like dinosaur. Based on the characteristics of its partial skeleton, the specimen has been scientifically sorted into a group of dinosaurs called the troodontids, which distantly preceded the Velociraptor species of the Cretaceous.

In its golden years, Hesperornithoides likely spent its days scurrying across the damp, sparsely vegetated earth of the Jurassic, picking off prey with its powerful, sickle-clawed feet. Though it had many avian-esque features, including feathered forelimbs, the species’ body proportions suggest it was flightless, study author Scott Hartman, a paleontologist at the University of Wisconsin-Madison, told Riley Black at Smithsonian. (Even on the ground, plumage has perks, and may have offered some dinosaurs insulation or a visual way to attract mates.)

This mish-mash of aerial and terrestrial traits echoes what’s been observed in other dinosaurs tentatively characterized as forerunners of modern birds. It’s too early to tell exactly where Hesperornithoides lands in its family tree, and there’s nothing to say that its lineage directly gave rise to modern birds. But Lori’s skeleton provides further evidence that many of the features associated with birds, like primitive wings and feathers, may have had their start in entirely ground-based creatures—and likely arose quite some time before flight itself, Hartman told John Pickrell at National Geographic.

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A reconstruction of Lori, a specimen of Hesperornithoides miessleri. Over 40 percent of Lori's skeleton was recovered. Image Credit: Hartman et al., PeerJ, 2019

Hesperornithoides’ transitional appearance also builds the case for flight not being a one-off adaptation. Fossils of bird-like dinosaurs are present all over the world, and several lineages seem to have charted independent paths into the skies. “It’s pretty clear that flight evolved in dinosaurs more than once, and this new dataset supports that,” Jingmai O’Connor, a paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing who was not involved in the study, told Pickrell.

Until more specimens of this species are found, Hesperornithoides can’t be pigeonholed. If anything, the discovery of this carnivorous chicken lookalike shows that, when it comes to evolution, the picture can always get more complex.

As for the simple stories? Well—those are still for the birds.

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