Assistant Professor of Geology Whitey Hagadorn (left) shows Martha Buck ’04
and Colin Porter ’05 the extraordinary level of detail captured by a micro-focus
CT scan of a trilobite. |
Professor Hagadorn’s Precambrian preemies
On the top floor of the Pratt Museum, amid the building’s bones and
stones and creaking floors, is a bit of cutting-edge technology that seems strikingly
out of place. It is a micro-focus CT scanner, a device that one researcher said
is most often used by the government for “research that never gets published.” The
four-foot-long tabletop scanner operates on the same principle as the large ring-shaped
CT scanners used in hospitals, but is designed for microscopic subjects. The
device is in the laboratory of Assistant Professor of Geology Whitey Hagadorn,
who is perhaps the only person in the world using a micro-scanner to image fossils.
Hagadorn uses the scanner to study features that are normally inaccessible to
paleontologists: the interior and soft body parts of specimens that cannot be
removed from their surrounding matrix. “Although it’s very easy to
extract a dinosaur bone from sandstone,” Hagadorn says, “it’s
very difficult to extract impressions of the soft tissues of an organism out
of a shale or a sandstone or some other rock. It’s also very difficult
to extract, say, pyritized fossils from shale—that is, fossils preserved
as fool’s gold.”
The ability to scan soft body parts is
especially useful given Hagadorn’s main area of research. He studies the
Neoproterozoic/Cambrian interval, the
period of 500-600 million years ago, when animal life first appears in the fossil
record and before bones and shells had fully appeared. “It’s exciting,” he
says, “because animals produce a profound change on the surface of the
Earth, with respect to the chemistry of the oceans, the deposition of sediments,
and the habitation of sea-floor environments and the water column. It’s
as though you have this ecological barrel that is empty and then suddenly becomes
filled with what seem to be rapidly evolving, rapidly reproducing critters.”
Those “reproducing critters” are the subjects of Hagadorn’s
most important
research. He is working on a site in China that preserves the oldest evidence
of animal life ever found: embryos that are 590 million years old. These embryos
are
extremely tiny—only 100 to 500 microns
in diameter (slightly wider than a human hair)—and are in the earliest
stages of cell division. Scientists originally thought they were algae, but once
researchers were able to remove some of the tiny fossils from the rock, an electron
microscope revealed the specimens to be animal embryos. “They looked somewhat
like soccer balls,” Hagadorn says. “The embryos stayed the same size,
but they had a variety of different cleavage states, which is just what you see
in the initial stages of cleavage in animal embryos, as opposed to algae or other
plants, where the size of the embryo gets larger as they cleave.”
Though the electron microscope gave scientists a clear picture of the outside
of the embryos, it could not show the interior. That’s where Hagadorn’s
technique comes in. On his computer screen, the micro-focus scanner’s remarkable
three-dimensional image slowly rotates, showing the full interior of the embryo,
not only the cells themselves, but also smaller internal structures. Hagadorn
and his research partner, Shuhai Xiao of Tulane University, were the first to
look inside the embryos and provide information on their structure and development.
So far, they have identified nine different morphotypes, which may represent
nine different species or just nine stages of one. Hagadorn hopes to scan a wide
enough sample of the fossils to determine how many species there might be and
to reconstruct their communities and environment.
The harder task will be figuring out what animal the embryos represent. They
may have been sponges or brachiopods, jellyfish or something else. “You
might think ‘Oh, that’s easy. You just look at it,’” Hagadorn
says. “But how do we identify an organism based on a modern analogue? We’ve
got a pretty good idea what a mammoth is because we’ve got modern elephants.
If there weren’t any of those, we would have no idea. When you go back
500 to 600 million years ago, it becomes increasingly difficult to do that.”
Hagadorn’s interest in CT scanning started in 1999, when he was doing post-doctoral
paleontological research at
the California Institute of Technology. Because he was the only paleontologist
there, all fossil questions came to him. One day a man wanted to know if a
dinosaur egg that he had bought in China was genuine. When Hagadorn concluded
that it was manmade, the man refused the diagnosis, saying that he was going
to take the egg to a friend who operated the CT scanner at a local hospital,
believing that the scan would prove its validity. The scan actually confirmed
the forgery, but the egg did hatch an idea for Hagadorn, who realized that CT
scanning could allow him to see inside fossils without destroying them.
No one had ever used a micro-focus CT scanner this way, so Hagadorn had to teach
himself. He got permission to use a scanner at Cal Tech’s affiliate institution
the Jet Propulsion Laboratory, and spent two years trying different techniques.
He eventually learned how to scan every mode of preservation in almost all rock
types. “All of this was just trial and error,” he says. “It
wasn’t like there was a manual to read on how to do that. CT scanning a
bone is dead easy. CT scanning a bone in rock, or a trilobite in rock, is a totally
different story. I sat there for two years and just cranked on this.”
Hagadorn’s efforts have been acknowledged by several major grants, including
one from the National Science Foundation that will help pay for a new higher-resolution
scanner. The new machine, he says, should help him get even closer to identifying
our earliest ancestors.
Online extra: See
fossil images from the micro-focus CT scanner in "Beecher's Trilobite Bed,"
a senior thesis by Martha Buck '04
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Photo: Frank Ward
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