'Wonderchicken': oldest fossil of modern bird discovered

March 18, 2020

Asteriornis maastrichtensis lived 66.7 million years ago, less than a million years before the asteroid impact that doomed all nonavian dinosaurs. The winged and beaked descendants of this quail-sized bird, however, survived that mass extinction event, forming a long lineage that includes modern chickens and ducks.

Based on analyses of fossil remains, which consist of a nearly complete skull and a few limb bones, the bird is closely related to the most recent common ancestor of land fowl and waterfowl, researchers report March 18 in Nature.

A. maastrichtensis’ skull is “a never previously seen mashup of ducklike and chickenlike features,” says Daniel Field, a vertebrate paleontologist at the University of Cambridge. “It’s like a turducken.”

Previous estimates, based on molecular analyses of living bird groups, suggest that modern birds evolved before the mass extinction event roughly 66 million years ago. But this is the first fossil to definitively place a modern ancestor on the scene. The age of the fossil, in fact, suggests that those previous estimates, ranging from 139 million to 89 million years ago, might have overestimated how early these birds arose, Kevin Padian, a vertebrate paleontologist at the University of California, Berkeley, writes in a commentary in the same issue of Nature.

Modern-type birds share several key traits, such as toothless beaks and fused foot bones. The almost 11,000 living bird species — the paleognaths (flightless birds such as ostriches), anseriformes (waterfowl), galliformes (land fowl) and neoaves (the remaining 95 percent of living bird species) — all share a common ancestor, Field says. “We think that ancestor lived at some time before the end of the Age of Dinosaurs,” he says. But there are very few bird fossils surviving from before the asteroid impact.

The new fossils were discovered in Belgium, in a small rock about the size of a digital camera battery. The rock, made of hardened marine sediments, looked like nothing special from the outside, Field says, just “a few broken bird limb bones poking out.” But any bird bones dating to just before the mass extinction event were intriguing enough that he wanted a closer look.

While many birds lived alongside the dinosaurs, the majority were members of archaic groups, such as the toothed Enantiornithes, which went extinct along with most of the larger land animals. All modern birds emerged from a single group called the Neornithes, which appeared toward the end of the Cretaceous.

Until now, most fossils of birds from the Cretaceous that were related to living species have been “fragmentary and dubious,” she says, but the new discovery hints at the potential to find additional well-preserved modern bird relatives that lived prior to the impact and extinction event.

Sources: https://www.nationalgeographic.com/science/2020/03/early-bird-wonderchicken-walked-earth-with-dinosaurs/, https://www.sciencenews.org/article/wonderchicken-fossil-earliest-known-modern-bird