A big surprise is revealed in this soft x-ray absorption image of exoskeleton from a 310-million-year-old scorpion fossil. The brighter areas map the abundance of nitrogen from chitin, which scientists previously believed couldn’t endure in extremely old fossils. For scale, the black bar is one-millionth of a meter. Credit: Carnegie Institution |
It’s not quite Jurassic
Park, but who wants
Paleozoic scorpions scurrying around anyway? Scientists used a powerful
microscope at the U.S. Department of Energy’s Lawrence Berkeley National
Laboratory (Berkeley Lab) to detect remnants of protein and chitin in the
exoskeleton of a 417-million-year-old fossil of an extinct mega-scorpion, a
discovery that is several hundred million years older than previously thought
possible.
The finding was made by a team of scientists led by George
Cody of the Carnegie Institution of Washington. The research was conducted at
the Advanced Light Source, a synchrotron located at Berkeley Lab.
Their work upends the conventional view that organic material,
such as that found in the outer portion of exoskeleton, doesn’t endure in
extremely old fossils because it’s readily broken down by hungry microbes and
other natural processes. The outer layer of exoskeleton is composed of a
fibrous weave of chitin, a polysaccharide rich in nitrogen, embedded in a
matrix of structural proteins.
The scientists found the molecular signature of this
material in a 417-million-year-old eurypterid fossil, an extinct arthropod that
resembles an enormous scorpion. Some eurypterid species measured six feet long.
They also found chitin-protein complex in a 310-million-year-old scorpion
fossil. Previously, the oldest evidence of chitin dates to 25-million-year-old
fossils.
“It turns out that vestiges of chitin and structural protein
are abundant in much older fossils than we thought. Who knows what other
surprises we’ll find when we search for organic material in even older
fossils,” says Cody, the lead author of an article on this research that was published
online by Geology.
Scientists have used mass spectrometry to detect chitin in
fossils from the Cenozoic era, which spans from today to when the dinosaurs
became extinct 65 million years ago. But the trail grows cold further back in
time. Analyses of shrimp, eurypterid, and scorpion fossils dating from the
Paleozoic era, which spans from 542 to 251 million years ago, failed to uncover
evidence of chitin. This led scientists to conclude that fossilized chitin is
whittled away to nothing by millions of years of degradation.
Scientists at beamline 5.3.2 of Berkeley Lab’s Advanced Light Source. Credit: Lawrence Berkeley National Laboratory |
Cody’s team tried a new approach to hunt for chitin-protein
complex. They turned to beamline 5.3.2 of the Advanced Light Source, a national
user facility that generates intense x-rays to probe the fundamental properties
of substances.
The beamline boasts a state-of-the-art scanning transmission
x-ray microscope that can produce nanoscale images of materials. It can also
perform an analytic technique, called x-ray absorption near edge structure
spectroscopy, which identifies atoms of individual elements, within their
molecular framework, by probing their electrons at distinctive energies.
Beamline 5.3.2 is specially tuned to detect carbon, nitrogen, and oxygen atoms.
The beamline instrumentation was developed by Berkeley Lab’s
David Kilcoyne, who previously teamed up with Cody to catalog the chemical
makeup of meteorites and comet dust. Other scientists have used the beamline to
explore the characteristics of carbon nanotubes and study air pollution
samples, among many applications.
In this research, Cody and Kilcoyne studied the fossil
remains of two Paleozoic arthropods: a scorpion unearthed in a cave in northern
Illinois, and a eurypterid plucked from a
quarry in Ontario, Canada. In both fossils, x-ray
absorption near edge structure analyses revealed that much of the carbon,
nitrogen, and oxygen detected in the exoskeleton are from chitin-protein
complex.
“The microscope at the Advanced Light Source is the star in
this research,” says Cody. “It opens up new ways of conducting molecular
paleontology research.”
Cody believes the preservation of chitin-protein residues in
extremely old fossils likely depends on the build up of fatty acids on a
scaffold of chitin-protein molecules. This layer saves the remaining matrix of
chitin and proteins from degradation by microorganisms even after 500 million
years.
The research was funded in part by the NASA Astrobiology
Institute and the Massachusetts Institute of Technology.
