No bones about it
Scientists find traces of life without relying on the usual fossils
Posted April 8, 2011
The two snowmobiles quickly turn to small specks on the white snowfield. Mountaineer Brian McCullough is in the lead, a thick rope secures his machine to one driven by scientist Stephen Hasiotis.
The two men are also harnessed and roped together. They’re making the first snowmobile traverse on this route to a feature called Wahl Glacier. A trail from a large field camp in the central Transantarctic Mountains had led them more than halfway, threading through a crevasse field, and up and down rises in the valley.
Now they’re in virgin territory, and McCullough expertly steers to a large rock outcrop the team has dubbed “the castle” near Wahl Glacier. Hasiotis, a paleontologist from the University of Kansas, hopes to add to an already impressive trove of finds based on previous reports of fossils in the area.
Hasiotis isn’t your typical Antarctic fossil hunter.
First, there’s the headgear — a worn, leather cowboy hat that stays as firmly on his pony-tailed head as Indiana Jones’ fedora. There’s also a bit of cowboy swagger in the first-generation Greek-American, as well as an infectious enthusiasm for his work. He’s quite eager to jump down onto his belly, arms and legs swinging, to illustrate how a burrowing critter that lived in a warmer Antarctica long ago might have scurried and clawed through its underground home.
Hasiotis occupies a relatively rare position in the world of paleontology as an ichnologist. No, it has nothing to do with the study of fish, he admonishes, unless maybe you’re talking about the fossilized burrows left behind by lungfish tens of millions of years ago.
Ichnology is the study of the “traces” created by animals, such as burrows, footprints and tracks. Hasiotis is an expert in paleoichnology, which involves trace fossils created by organisms that lived in the distant past.
In the case of the team’s fieldwork in Antarctica, the period is a few tens of millions of years on either side of the Permian-Triassic boundary. That’s the time about 250 million years ago when the world’s largest extinction event occurred, wiping out about 96 percent of marine species and 70 percent of terrestrial ones.
The southern continents were still stitched together in the supercontinent Gondwana. The icehouse that dominated during the end of the Carboniferous period about 300 million years ago had thawed into a greenhouse. Swamps and forests, lakes and rivers, with primitive flora and fauna, blossomed as the ice sheet and glaciers retreated.
Over countless millennia this basin near the modern-day Beardmore Glacier filled with sediments as tectonic plates shifted, rifts formed and mountains rose. “Basically, we’re like a bunch of time trackers. We’re going through the pages of the past, which are these layers of sediments,” says Hasiotis, never at a loss for metaphors.
Peter Flaig is the team’s expert on those sediments. His job is to put the trace fossils into context. For example, if Hasiotis spies what be believes are the swimming trails of a fish — where it might have settled on the sediment, leaving an imprint — Flaig must determine if the sediment deposits indeed belong to a lake.
“So we have some idea of where the animals are living, not just what they’re leaving behind,” explains Flaig, a postdoctoral fellow from the University of Texas at Austin.
Re-imagining what the region was like provides clues not only to the environment at certain snapshots in time, but information about the evolution of this sector of the Transantarctic Mountains and the events surrounding the P-T boundary extinction.
“If we’re really going to understand these extinction events, we need to understand how they express themselves in all different environments here,” Flaig says.
Hasiotis is shouting for Flaig, and a few expletives pepper his exclamations as he scrambles underneath an overhang on the castle-like outcrop near Wahl Glacier, which looks nearly sheer from this vantage point, a few bare rocks jutting out from the ice.
Underneath the overhang, Hasiotis points to a smooth, rounded formation, conspicuous only to his well-trained eye among the roughly carved rocks. It’s a burrow, he says convincingly, amazed at the size. He can only guess at the critter that might have built it. Perhaps some sort of therapsid, a mammal-like reptile that flourished from 275 to 205 million years ago. They are thought to have been the precursors of mammals.
Direct body fossil evidence of such creatures from that period is frustratingly scarce in Antarctica, aside from the traces that Hasiotis and others have discovered. But similar burrows with bones excavated in South Africa are nearly similar, allowing scientists to speculate on the types of animals that once lived on this part of the continent.
The lack of body fossils isn’t surprising, given the special environmental conditions that must exist for preservation. It’s really a matter of odds, Hasiotis notes. “You and I only have one body to give to science, but we can make millions of tracks and trails and traces in a lifetime,” he says.
Hasiotis snaps dozens of digital pictures of the find, with hopes of returning in the few weeks he has left in Antarctica this season. It will require shuffling priorities, as weather has already wreaked its usual havoc on the field schedule. First, there were delays at McMurdo Station. Then the team got stuck nearly an extra week at a nearby locale called Graphite Peak when the weather prevented a helicopter from reaching the site.
Despite such setbacks, the rewards have been many. And they keep coming, as Hasiotis, Flaig and McCullough scramble down the castle outcrop, zipping over to another area of exposed rock a minute’s ride away.
Flaig had explored this site back in 2003 during his first trip to Antarctica, when a similar field camp was established in this slice of the central Transantarctic Mountains for similar geological and paleontological research now under way. It doesn’t take long for him to find the tree stumps.
Yes, trees in Antarctica. The discovery itself is not new, but Hasiotis is particularly jazzed about an earlier find at a different site that unleashes his imagination of what might have transpired so long ago.
The blackened rock he displayed previously back at camp can only be one thing — fossilized charred wood.
“There were forest fires in Antarctica 260 million years ago,” he says. “We have evidence that there were forest fires that would rage in the summer time in Antarctica 260 million years ago.”
Such trees would have stood in a swamp, though lightning strikes could have conceivably sparked the fuel sitting at the trunks of this ancient forest during droughts. Still, even the most creative imagination — and best scientific mind — struggles to put together a comprehensive picture of Antarctica in the Permian-Triassic.
The most well-accepted story of the period suggests that the climate shifted from wet and warm to dry and warmer at the boundary. But those interpretations are inherently biased, based on the evidence at hand. Sedimentologists like Flaig assume the Triassic dried out based on the sand that filled the basin. But so much of the evidence is covered by ice in today’s Antarctica.
We only get what [is] exposed,” Flaig says. “We only have what these mountains give us.”
This season the mountains have been kind to Hasiotis, a relative newcomer to the U.S. Antarctic Program. His one and only previous season was in 1997, working with a team on fossils near the Shackleton Glacier farther south.
Inside a heated RAC tent at the CTAM field camp, Hasiotis takes stock of his growing pile of fossils, wrapping them in burlap bags and placing them in rock boxes for transportation back to the University of Kansas.
On one flat, grayish rock slab, angled just right to catch the light, uniform prints march across the face — almost like small, four-fingered handprints from a stick figure. Hasiotis asks a visitor to guess what might have made the traces.
“There were horseshoe crabs living in freshwater rivers and lakes in Antarctica 245-250 million years ago,” he enthuses. “This is very diagnostic of horseshoe crabs. That’s the pattern they make.”
If correct, it would be the first such discovery of horseshoe crabs in Antarctica. Today’s horseshoe crabs live in marine environments, not fresh water. Hasiotis says the formation of the supercontinent probably played a role in the evolutionary history of the crabs, forcing them into a fresh water environment when other habitats may have disappeared.
“Trace fossils are like fingerprints. They don’t tell you genus or species, but it can tell you horseshoe crab,” he says. “We’ve hit the jackpot on this trip between the tracks of animals we don’t even know about, the horseshoe crabs, and the small burrowing therapsids or reptiles.”
NSF-funded research in this article: Stephen Hasiotis, University of Kansas, Award No. 0944282.
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