Behold the Wonderchicken,
the earliest modern bird ever found.
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.
So Field and his colleagues
used computed tomography, a kind of X-ray scanning, to peer inside the rock.
And that’s when they saw the skull. The team knew right away they had something
special. “The timeline was: See the skull, scream ‘Holy shit,’ give my Ph.D.
student a high five, and then start calling it the Wonderchicken.”
The front part of the skull
is chickenlike, including the nasal bone that formed part of the nostril, helping
to shape its beak. “A barnyard chicken will eat anything you put in front of
it,” Field says, and that’s reflected in the chicken’s nonspecialized beak
shape. That’s in contrast to other birds, which have beaks clearly specialized
for their particular diets — think the tearing bill of a raptor or the long
slender sipping beak of a hummingbird.
That beak shape suggests
that, like chickens, the ancient bird was also not a picky eater. And that may
have been a crucial trait, Field says. “An unspecialized diet is the kind of
feature that might have helped animals like the Wonderchicken survive” after
the asteroid impact.
But part of the skull is
more characteristic of waterfowl like ducks. Those features include a
distinctive bone that projects from the back of the skull out to the base of
the eye socket and a hooked bone at the back of the jaw. Analyses of the limb
bones, meanwhile, suggest that A. maastrichtensis had fairly long legs.
The rock containing the fossils consists of marine sediments, suggesting that the
bird was a shorebird.
“This is one of the most
important bird fossils that has been found in quite some time,” says Stephen
Brusatte, a vertebrate paleontologist at the
University of Edinburgh, who was not involved in the study. “It raises the
intriguing possibility that small size and a shoreline habitat may have helped
these birds survive the end-Cretaceous extinction” when so many other, larger
dinosaurs did not.