91av

PALAEONTOLOGISTS claim to have found feathers on a lizard-sized reptile that
evolved 220 million years ago, 70 million years before the oldest known bird,
Archaeopteryx.

The long-neglected fossil, called Longisquama insignis, has
reignited the debate over whether birds are feathered dinosaurs or whether they
evolved from earlier reptiles. “It’s a stake in the heart of the dinosaur
theory, which I haven’t believed in years,” says Storrs Olson of the Smithsonian
Institution in Washington DC. But many experts doubt the fossil shows feathers
or was even related to birds.

Russian palaeontologist Alexander Sharov found the fossil in Kyrgyzstan some
30 years ago. It shows only the front 5 centimetres of the body, with elongated
scales covering the chin, neck and backs of the front limbs.

Most intriguing are the six to eight paired flat structures about a
centimetre wide and up to 14 centimetres long. These rise up from near the
backbone, and a group of palaeontologists and ornithologists including Alan
Feduccia of the University of North Carolina in Chapel Hill insists the
structures are feathers which lack only a few modern details. They say the
structures have hollow central shafts with barbs branching from them, as in
modern feathers, but they lack the barbules that hold barbs together
(see 91av, Inside Science, 17 June).

However, Richard Prum, an ornithologist at the University of Kansas Natural
History Museum in Lawrence, points out that the structures are transparent,
unlike modern feathers. What appear to be barbs branching from the shaft are
instead wrinkles in a continuous fossilised membrane, he says. Hans-Dieter Sues,
vice-president of the Royal Ontario Museum in Toronto, agrees: “They are highly
specialised scales that are superficially feather-like in being elongate and
having a midline ridge.”

Whether they are feathers or scales, the structures are longer than the
animal’s body and appear to be attached to back muscles, not limbs. Feduccia
thinks Longisquama unfolded them on either side of its back, making it
“quite a remarkable glider”. Sues, on the other hand, thinks they may have been
used for display, as in some modern lizards, and doubts they could have
folded.

“We’re not claiming that Longisquama is the ancestor of birds,” says
Feduccia. But he believes the fossil shows that birds did not evolve from
dinosaurs, but from an earlier group of reptiles. Sues and others say the fossil
is not complete enough to be sure, and criticise Feduccia’s group for not using
the now-standard cladistic technique to establish Longisquama’s
relationship to other groups.

The debate, however, threatens to overshadow the importance of
Longisquama’s peculiar and elaborate ornaments. Even if the structures
aren’t feathers, they clearly evolved from reptilian scales. Sues says they are
unique: “I know of no other example from any geologic age.”