Ted Daeschler, of the Academy of Natural Sciences of Drexel University, does it at the ends of the earth.

The Philadelphia scientist and his colleagues have earned international renown for their discovery of prehistoric fossil fish above the Arctic Circle, on Canada's Ellesmere Island.

Now they are at the other end of the globe, in Antarctica, prospecting for fish fossils from 385 million years ago.

Daeschler, who is due back in Philadelphia this week, is interested in that prehistoric era in part because of what was happening in the tree of life.

During the Devonian period, certain species of fish had evolved muscular "lobed" fins, in some cases enabling them to scurry onto land for short stretches. Their descendants eventually gave rise to mammals.

The Devonian takes its name from Devon, England, where sediment from that period was first identified.

Though it may seem incongruous to hunt for fish in the frozen reaches of the Canadian Arctic and the Antarctic, both land masses were located closer to the Equator 385 million years ago, and their climates were warmer and wetter.

During Daeschler's Antarctic excursion over the last several weeks, the temperatures never rose above freezing, usually hovering between 15 and 20 degrees Fahrenheit.

The trip began in early December, with five colleagues who included University of Chicago paleontologist Neil Shubin, formerly of the University of Pennsylvania.

First the team flew to New Zealand over two days, followed by an eight-hour flight in a military cargo plane to the Ross Ice Shelf of the Antarctic.

Then it was a 45-minute drive on an "ice road" to McMurdo Station, a scientific support facility built on a ridge of volcanic rock.

They were stuck there for a couple of days due to fog and blowing snow, but eventually helicoptered to the first in a series of remote campsites.

The team has been exploring deposits of siltstone, and has found bony plates from long-ago armored fish, primitive shark teeth, and the remains of early ray-finned and lobe-finned fish, Daeschler wrote in his blog.

The group had to be very careful, Daeschler wrote in an email:

"Tents must be properly configured to avoid blowing away. Hydration is very important and all water must be melted from snow. Sun exposure can be an issue, including snow blindness. Crossing snow field and permanent snow/glaciers needs to be done carefully (sometimes with mountaineering ropes) to avoid slipping and sliding down slopes, or falling in crevasses."

For the last few weeks, Daeschler's automatic email response has read as follows.

"I am out of the office for field work in the southern hemisphere."

He has been within 800 or 900 miles of the South Pole, so that is putting it mildly.

For fossil-hunters who would prefer to stay close to home, fish from the Devonian period also can be found in Pennsylvania.