LIFE & EVOLUTION
Possible lungs preserved in bird fossil
But some paleontologists are skeptical of the one-of-a-kind find
BY CAROLYN GRAMLING
An ancient bird fossil that appears to contain preserved lung tissue may breathe
new life into studies of early avian respiration. If confirmed as lungs, the find
marks the first time scientists have spotted the respiratory organs in a bird fossil.
Scientists have previously described
fossils of Archaeorhynchus spathula,
among the earliest members of the lineage that led to modern birds. But unlike
those fossils, a newly described specimen
dating to about 120 million years ago has
significant traces of plumage and the
probable remnants of a pair of lungs, vertebrate paleontologist Jingmai O’Connor
and colleagues announced October 18.
It’s rare for soft tissue to survive fossilization. But scientists are increasingly
finding preserved feathers, skin and even
bits of brain (SN: 11/26/16, p. 9). Fossilized lungs are also not unheard of: The
organs have been preserved with the
fossils of a salamander and a mammal
(SN Online: 10/21/15).
“But we’re arguing that this is the first
lung tissue preservation that is anatomically informative,” said O’Connor, of the
Institute of Vertebrate Paleontology and
Paleoanthropology in Beijing.
That’s because modern birds have a
highly specialized and efficient respiratory system that allows them to absorb
enough oxygen to meet the demands of
powered flight. Unlike mammalian lungs
that are elastic and pump air in and out,
bird lungs don’t change size when the
bird breathes. Instead, several air sacs
connected to the lungs act like a bellows
to draw the air in through the lungs. The
lungs themselves contain highly subdivided tissue with tiny air capillaries
that transfer oxygen and carbon dioxide.
The newly described Archaeorhynchus
fossil contains many of the same structures, O’Connor’s team reported online
October 22 in the Proceedings of the
National Academy of Sciences, suggesting that these respiratory adaptations
This Archaeorhynchus spathula fossil reportedly
preserves the ancient bird’s lungs (outlined at
top) and stomach.
existed early in the modern bird lineage.
The Archaeorhynchus specimen is split
into two halves, a main slab and its mir-
ror image called a counterslab. Both slabs
have unusual features. The chest cavity
on the main slab contains a white speckly
region. And the counterslab has two
nearly symmetrical lobe-shaped regions
corresponding to the speckly region. The
lobes’ position, and that there were two
of them, suggests the possibility of lungs,
O’Connor said. The structures were
unlikely to be stomach contents, which
usually appear black and carbonized in
fossils. And the liver tends to appear red-
dish due to its high iron content.
O’Connor’s team used scanning elec-
tron microscopy to study 22 samples
from the fossil, including 12 from the
purported lungs. The images revealed a
highly subdivided region of tissue known
as the parenchymatous region, which had
many closely packed air cells. That struc-
ture is similar to the air capillaries found
in small modern birds, O’Connor noted.
Still, other scientists aren’t convinced
that the material represents lungs. “I’d
T. rex pulverized bones with intense force
A lethal combination of a powerful bite, strong teeth and repeated crunching
let Tyrannosaurus rex pulverize its prey’s bones, researchers said October 20.
To access nutritious bone marrow, most bone crushers have to be able to
clamp their jaws together to crunch through the dense outer layer of bone.
Some carnivorous mammals, like spotted hyenas, can do this. But bone-crushing is unknown among living reptiles because their upper and lower
teeth don’t fit together, or occlude, in a way that allows clamping.
Tyrannosaurs didn’t have occluding teeth either, but the dinosaurs still
crunched bone. To figure out how, anatomist Paul Gignac of Oklahoma State
University in Tulsa and vertebrate paleontologist Gregory Erickson of Florida
State University in Tallahassee examined fossil evidence of the creatures’
dining behavior. The duo also investigated the bite forces of modern birds and
crocodiles. Extrapolating from that evidence, the researchers estimated T. rex’s
bite force to be as much as about 34,000 newtons — more than twice as strong
as a crocodile’s bite force, the strongest of all living animals. And the tip of each
tooth could exert up to about 3,000 megapascals; that intense pressure would
help create cracks that weakened bone. Fossil evidence suggests that T. rex
would also gnaw at one spot, further weakening the bone. — Carolyn Gramling
very much like it to be true, but there are
a few too many question marks about
how such tissues could have been preserved,” says vertebrate paleontologist
Corwin Sullivan of the University of
Alberta in Edmonton, Canada.
“I knew that a lot of people would be
rightfully skeptical,” O’Connor said. But
bird lungs have some sturdy structures
that may have aided preservation, or
perhaps the environment in which the
bird died was particularly conducive to
preservation. But these are just hypothe-ses, O’Connor said. The team is planning
research to address this and other questions about how this bird breathed. s