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Spring 2006
by Eric Schoeniger
With the discovery of a sensational new fossil that fills the gap between fins and feet, Ted Daeschler ’81 saunters into the paleontology pantheon
In July 1999 a half-dozen scientists were deposited by helicopter in the raw expanse of Arctic Canada, six hundred miles above the Arctic Circle. Their objective was nothing short of audacious: to scour an area nearly twice that of Pennsylvania for a few fossilized bones that could be assembled into a proverbial “missing link.”
Five years and four expeditions later they had achieved their goal. In 2004, they emerged from the tundra with Tiktaalik roseae (pictured above, right), a 375-million-year-old creature that fills a conspicuous gap in the fossil record between finned fishes that swam in water and limbed animals that walked on land. In April of this year they published their findings in Nature, where it appeared as the cover story.
“Tiktaalik is significant because it occurs during a major transformation in the history of life, when vertebrates first began experimenting with walking on land. All limbed animals, including humans, are the descendents of one of those experiments,” says Ted Daeschler, Ph.D. ’81, who was co-leader of the expedition along with Neil Shubin of the University of Chicago. Their chief collaborator was Farish Jenkins of Harvard University.
In fact, Tiktaalik (pronounced tick-TAH-lick) set off a minor media frenzy, at least for a fossil, with stories in outlets such as The New York Times and National Public Radio. Other scientists have called the find a “Rosetta Stone” and “an amazing, important discovery.”
Talking up fossils
Unearthing Tiktaalik is only the latest accomplishment of Daeschler’s, who is assistant curator and chair of the vertebrate zoology department at the Academy of Natural Sciences in Philadelphia. In the mid-1990s he and Shubin made similar discoveries in Pennsylvania that landed them an interview with Ted Koppel.
Daeschler’s office at the Academy looks like what you’d expect a paleontologist’s office to look like, with heaps of books and papers, a row of anemic houseplants along the windowsill, and a cloudy green aquarium that’s home to an eight-inch progenetic salamander in its larval form. But Daeschler hardly fits the stereotype of a preoccupied scientist. He’s engaging and gregarious, greeting colleagues cheerfully as he hurries through the Academy’s labyrinthine hallways.
Still, he’s most enthusiastic when talking about fossils. The first thing he wants to show a visitor is Tiktaalik, eager to point out the shape of the skull, the sturdy ribs, the scales on its back preserved in exquisite detail. “It’s extremely rare for a fossil of this age to be in such good condition,” he says.
Tiktaalik roseae is a transitional species between lobe-finned fish and tetrapods of the Devonian.
He’s equally excited by the life-size artist’s model, which shows how Tiktaalik might have appeared lurking in the shallows of a Paleozoic stream. The creature looks like a fishy alligator with an abashed grin, as if it’s not quite comfortable with its newfound celebrity. The back end of the model ends abruptly, because that portion of its skeleton was never found.
Deciphering the Devonian
When we think of paleontology, we generally think of dinosaurs. But Daeschler is interested in creatures far older. In particular, he focuses on fossils from the Late Devonian (named for Devon, England, where rocks from the period were first studied), 380 to 360 million years ago. It was a period of rapid and significant evolutionary change.
For much of its history, Earth was brown and comparatively barren. The Devonian saw the emergence of the first mosses and ferns and, eventually, seed-bearing plants and trees. Around the same time, insects and spiders began crawling the newly green landscape.
But much of the action was still under water. In fact, the Devonian is sometimes called the Age of Fishes. In addition to now-extinct groups such as armored fish and spiny sharks, there was a sudden diversification of ray-finned fish (think salmon or tuna) and lobe-finned fish.
By the end of the Devonian, the first tetrapods, or four-footed vertebrates, had also emerged. It was an ideal time for terrestrial experimentation. As deciduous plants flourished in shallow streams, they attracted small prey into oxygen-poor water. A fish that had the appendages—and lungs—to navigate these shallows could feast on that prey and avoid being eaten by predators farther downstream.
It has long been believed that lobe-finned fish, with their bony, muscular extremities, were the direct ancestors of tetrapods. But there were precious few fossils that reflected this transition from water to land. “There was a gap of 10?–15 million years where we didn’t know much about what was going on,” Daeschler explains.
“Tiktaalik splits the difference” between fish and tetrapod “in both characteristics and time,” he continues. The creature is clearly a fish, with gills, scales, and fins. But those fins are supported by bones and muscles that aren’t found in earlier fish. In fact, a Tiktaalik fin comprises a single bone followed by a pair of bones followed by a number of smaller bones that are tantalizingly homologous to the humerus, radius, and ulna, and wrist bones in a human arm.
“Tiktaalik was probably a poor swimmer,” Daeschler says. “But it has shoulders and elbows and forelimbs that would allow it to push itself up off the ground, or even move around on land, at least for short trips.”
Proto-limbs aren’t the only characteristics that make Tiktaalik akin to tetrapods. The animal also had a neck. So unlike a fish, it could swivel its head up and down and side to side—an adaptation useful to life out of the water. What’s more, Tiktaalik’s skull is flattened like a crocodile’s, with the eyes on top, suggesting that it spent its time in shallow water, peering up.
But Daeschler believes the flattened skull has more to do with respiration than with predation. Like many lobe-finned fish of the period, Tiktaalik sported both gills and lungs. But Tiktaalik’s gill system was less robust than that of earlier fish, so it was less adept at sucking water over its gills. Instead, it likely used its flattened head and wide jaws to squeeze water past them. For lung breathing, robust, interlocking ribs—more tetrapod than fish—enabled the creature to support its own weight out of water.
Describing Tiktaalik, Shubin has said, “It’s a fish. It’s a tetrapod. It’s a fishapod.”
Exploring Ellesmere Island
Daeschler and Shubin excavated Tiktaalik on Ellesmere Island, part of the recently established Nunavut Territory of Arctic Canada. They had previously found Devonian fossils in north-central Pennsylvania, a hundred miles or so north of the F&M campus. But Pennsylvania is covered with soil and forests and cities. Daeschler and Shubin sought an area where fossils would be more accessible. A geological map showed that Ellesmere Island had an abundance of Devonian rock, much of it exposed to the surface. (During the Devonian, North America and Europe were joined in a single land mass, with Ellesmere Island just above the equator and Pennsylvania just below it.)
Their first foray took place in 1999. But misgivings among the local government meant they weren’t able to dig where they had hoped. “They were afraid we would disturb the caribou population,” Daeschler explains. “They didn’t understand that we were only six people, with no motorized vehicles.” The expedition turned up plenty of fossils, but none of the lobe-finned fish.
The barren beauty of Ellesmere Island, 600 miles above the Arctic Circle.
When the team returned a year later, they worked more closely with the Inuit, and the resulting relationship has proved beneficial to both sides. Daeschler and his colleagues have shared their findings with local schools. And Inuit have joined them on some excavations. In fact, the Inuit named Tiktaalik, which is an Inuktitut word for a large freshwater fish. The fossils discovered on Ellesmere Island will eventually be returned to Nunavut.
On their third trip, in 2002, Daeschler and Shubin found the snout of a creature “that we recognized could be right at this transition” between fish and tetrapod, Daeschler says. What they didn’t yet know was that they had discovered Tiktaalik. But when they returned in 2004, “we found nothing but Tiktaalik,”
Daeschler recalls. In fact, they found parts of at least 10 such animals, the largest being nine feet long. “It was terribly exciting,” he says.
Because the Arctic summer is short, with winter storms blowing in by August, Daeschler and his team can dig only four or five weeks a year. Planning, however, takes months. With the nearest human settlement a 100-mile helicopter ride away, “we plan for every piece of equipment and every scrap of food we need,” Daeschler says.
Much of their food comes in the form of freeze-dried beef and turkey, which they rehydrate in a pressure cooker. But Daeschler makes sure his team eats well, stocking the larder with pre-expedition trips to Whole Foods and Starbucks. “Food is our only entertainment,” Daeschler reasons. “It’s important for morale.”
The cook tent is pitched some distance from sleeping tents, a precaution against polar bears. Safety is always a concern, so teams travel with a shotgun. But the “single most important piece of equipment” is a GPS satellite-tracking unit; with camp so close to magnetic north, a compass won’t even function.
Daeschler poses with the head of the Tiktaalik roseae.
Continuing the process
Fossils as old as Tiktaalik are brought back from the field still mostly encased in hard sedimentary rock. It’s the painstaking job of a preparator to slowly excavate the rock away and preserve the delicate fossil bone.
“Fieldwork is only the first step of discovery,” Daeschler notes. “Subsequent discoveries occur in the lab as fossil preparation proceeds and as we do the literature work to understand how the fossil compares to other fossils.” More than a year of study was required before Daeschler, Shubin, and Jenkins were ready to submit their findings to Nature.
Much of that analysis took place at the Academy of Natural Sciences, where Daeschler oversees the vertebrate paleontology, mammalogy, and herpetology research collections. Although the Academy is best known for its exhibition hall, among scientists it’s recognized as a premier research institute. Its collections are vast, even including Thomas Jefferson’s fossil collection.
Daeschler joined the Academy as a staff member after receiving a master’s degree in paleontology from the University of California at Berkeley. While at the Academy he earned a doctoral degree from the University of Pennsylvania, where he first worked with Shubin.
But Daeschler credits F&M, where he earned a B.S. in geology, as the starting point of his career. “I got a great geology background from F&M, and I couldn’t have asked for better preparation for graduate school,” he says.
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He cites Roger D.K. Thomas, the John Williamson Nevin Professor of Earth and Environment, as a particular influence. “I came out of F&M with a strong interest in historical geology, the history of the Earth,” he explains. “I realized that the history of life on Earth is a fascinating part of that story, which is why I started focusing on paleontology. Roger Thomas is the person who got me interested in that.”
Daeschler also acknowledges the value of a liberal arts education. “Paleontology requires a lot of communication,” he says. “I have to write proposals, meet with the board of trustees, do outreach for the Academy.” Most important, perhaps, is fund-raising, which Daeschler describes as “never ending.” For each expedition, transportation alone costs tens of thousands of dollars.
Past financial support has come from the Academy, the University of Chicago, Harvard University, the National Geographic Society, the National Science Foundation, and a generous anonymous donor. Daeschler hopes that fund-raising will be easier now that he and his colleagues have “transitional-fossil cachet”—a phrase only a paleontologist could use with a straight face.
More cachet may be in the offing, as Daeschler and company are all set to return to Ellesmere Island this summer. They’ve already shipped the
Starbucks.
