The skull of Hongshanornis, showing impressions of tiny teeth.
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Image from Chiappe et al., 2014.
The skull of Hongshanornis, showing impressions of tiny teeth.

Feathery Fossil Offers Insights into the Flight and Diet of an Early Bird

Birds are dinosaurs. That fact, once shocking, is now familiar and easily seen as living birds strut and flap about. Yet it’s easy to forget just how long avian dinosaurs have been around, and how quickly they evolved into feathery foreshadowings of living birds. A newly-described specimen of Hongshanornis longicresta, a roughly 125 million year old bird found in China, helps illustrate how quickly early birds evolved habits that we can still see in avian dinosaurs today.

Who the earliest bird actually was is a point of contention. That title has traditionally been held by the roughly 150 million year old Archaeopteryx, and, for some, the classic “urvogel” defines that elusive point where non-avian dinosaurs end and avian dinosaurs begin. Other experts disagree about the placement of Archaeopteryx and point to other candidates, such as the 160 million year old Anchiornis, as marking the beginnings of birds. The science isn’t set in stone yet. But the point is that by about 150 million years ago there were small, feathery theropod dinosaurs that set the ancestral body plan for an evolutionary flourishing of birds through the rest of the Mesozoic.

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One side of the new Hongshanornis specimen. Image from Chiappe et al., 2014.

Hongshanornis was part of this radiation, an Early Cretaceous bird that belonged to a subgroup called the ornithuromorphs. The avian was an early member of a large, persistent group that includes modern birds today. And while Hongshanornis was first named in 2005, a new specimen described by  Luis Chiappe and colleagues contains some Cretaceous clues not previously seen.

The first specimen of Hongshanornis was a mold of the skeleton preserved on two slabs. Only the voids where the bones once were and a smattering of feathers remained. But the new fossil preserves actual bone in addition to the spaces where the skeleton has disappeared. Whereas Hongshanornis was thought to be toothless based on the holotype, for example, the newly-described specimen has impressions of small, rounded teeth at the front of the upper and lower jaws. Along with thumb claws, the teeth of this bird were a persistent remnant of dinosaurian ancestry.

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An illustration of Hongshanornis, showing bone (white), molds left by bone (grey), and a close-up of the gastroliths. Image from Chiappe et al., 2014.

What was Hongshanornis using those teeth to grip? Stomach stones offer a clue. Around the fossil bird’s pelvis sits a cluster of gastroliths – intentionally-swallowed pebbles that would have helped grind hard food. Since another Hongshanornis was preserved with a last meal of seeds preserved inside, Chiappe and colleagues suggest, the early bird probably plucked up hard foods that the gizzard stones broke down. Birds can’t chew, and such stones process their meals for them.

Despite the teeth and claws, though, Hongshanornis looked and flew very much like small birds that flit about today. The Cretaceous avian was about the size of a cowbird or an oriole, and had broad, long wings with a fan-shaped set of tail feathers. Pairing those traces of feathers with skeletal anatomy, flight expert Michael Habib and coauthors figured out that Hongshanornis had wings much like those of a common starling. With such a wing shape, Hongshanornis likely flew in a manner similar to many small extant birds – flapping continuously at slow speeds, but alternating between flapping and flexing the wings at higher speeds. Consider that the next time you see a songbird flap-bounding through the air, continuing an aerodynamic tradition that goes back to the height of the Age of Dinosaurs.