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Simple filaments or clusters of filaments,
potential early stages of feather evolution that couldn’t heave an animal off
the ground, might have been of use for
insulation or courtship displays. Fancier
structures that weren’t flight-capable
may have given an aerodynamic boost
for animals rushing up steep slopes.
A few fragments of ancient feathers
or protofeathers have been found in
amber before, including bits from Lebanon, France and New Jersey. But none of
the previous finds from dinosaur times
have shown the diversity of the newly
described assemblage, McKellar says.
He and his colleagues found not only
what looks like an unbranched filament
but also what has been proposed as a possible second stage in feather evolution, a
cluster of filaments. Prum ranks the sec-ond-stage feathery bit as “really great”
and convincingly identified, but admits
to nagging reservations about how definitively the simple filament can be linked to
a dinosaur or bird instead of some other
Researchers suggest feathers evolved from single (stage I) then multiple (stage II)
filaments that later developed a central shaft (stage III) covered in barbs and barbules that further differentiated and branched (stages IV and V). Scientists have
found specimens in amber from stages I, II, IV and V of feather evolution.
Stage I Stage II Stage III Stage IV Stage V
source of debris snagged in amber.
A separate, striking amber specimen
shows a birdlike feather branching into
secondary twigs, or barbules, with hook-lets like those in modern bird feathers
that zip together side-by-side barbules
to make a tight, interlocked surface.
Barbules on another specimen spiral at
the base, a feature that allows a feather’s
elements to uncoil and pick up water.
Such feathers on a modern waterbird
ease diving by reducing trapped air, and
Back Story | FEATHERS ROCK
they allow parents to soak their feathers
in water and then ferry the drink back to
chicks. (McKellar notes that researchers know a lot about details of modern
bird feathers, thanks in large measure
to the aviation industry’s interest in
identifying what species get sucked into
airplane engines.)
None of the amber-trapped feathers
had original owners attached, so the
researchers can merely speculate that
the simpler specimens might be from
dinosaurs and the more complicated
structures from birds. “It’s a really neat
cross section of what had plumage during the late Cretaceous,” McKellar says.
c
McKellar, an invertebrate paleontologist, found most of the feather bits
as part of a Ph.D. project searching for
tiny, amber-encased wasps less
than 3 millimeters long. Under
the high-resolution scrutiny
required to find the insects, miniature
feather bits showed up, too.
h u
Paleontologist Jakob Vinther of the
University of Texas at Austin says he was
pretty excited when he heard McKellar
talk about the amber fossils. Vinther
has explored microscopic color-gener-ating features of fossil feathers and has
even reported signs of iridescent color.
He tried to persuade McKellar to give
up some small bits of his specimens
for examination by scanning electron
microscope. But McKellar, who averaged
a feathery find every 360 specimens or
so, says he’s not ready to sacrifice any of
the samples just yet. s
Depending on who’s counting, rock fossils of about
15 genera of nonbird dinosaurs have revealed feathers.
Add in fossils with less direct evidence of feathers,
such as knobs on bones where quills could have
attached, and the number soars into the 20s.
Most of these marvels have entered the scienti;c
literature since 1996, when a small but startling
Sinosauropteryx (illustrated below) fossil was
described as a bird. Paleontologists later hailed it
as a dinosaur despite patches along its spine of
short, simple ;laments, what’s now called “dinofuzz”
and proposed as the ;rst stage in the evolution of modern bird feathers. More
recently described dinosaur fossils such as Microraptor gui (illustrated above)
have featured more evolutionarily complex feathers with central shafts. In 2010,
a research team in China even reported evidence that a Similicaudipteryx spe-
cies replaced its feathers in birdlike molts. And a feathered
fossil ;ap has arisen about whether Archaeopteryx, long
touted as the ;rst known bird, was actually a dinosaur
with feathers. These glimpses of feathers on what were
once believed to be scaly reptiles have reinvigorated the notion,
;rst proposed in 1868, that modern birds evolved from the celebrity
carnivore lineage of theropod dinosaurs. — Susan Milius
15 genera of nonbird dinosaurs have revealed feathers.
