HARVARD GAZETTE ARCHIVES
Finding a fossilized needle in an Arctic haystack
Jenkins describes expedition to net fish-land animal link
By Alvin Powell
Harvard News Office
The first season searching Arctic Canada for a fossil that would illuminate how our ancestors first crawled onto land proved Harvard Professor Farish Jenkins' explorer's maxim: Never go any place for the first time.
A crew of six trudged through a barren landscape during the summer of 1999, finding the wrong sort of rocks scattered across the wrong sort of terrain. In addition to dealing with the frustration and isolation, researchers had to keep a wary eye peeled for predators, since the islands of Arctic Canada are the stomping grounds for polar bears. So along with their scientific gear, the researchers carried rifles in case of an encounter.
They eventually found a large fossil that first season, but not the one they were looking for. So when winter returned from its brief hiatus, the researchers went home defeated, but not discouraged.
It would take several more seasons, and a move east to Ellesmere Island, before the researchers would find their prize: a link between fish and land animals that they would name Tiktaalik roseae.
Tiktaalik would prove worth the wait. When announced in April 2006, the discovery was hailed as the long-sought "missing link," filling an evolutionary gap in the history of how fishlike creatures first crawled out of the shallow rivers to take their place on land.
Jenkins, Alexander Agassiz Professor of Zoology and curator of vertebrate paleontology, described the seven-year journey of discovery that led to Tiktaalik's unveiling during a talk before a packed Science Center lecture hall Thursday (May 25). Called "From Fins to Limbs," the hour-long talk gave the audience a taste of what it was like searching for the fossil and the science behind it.
Jenkins and colleagues from the Academy of Natural Sciences of Philadelphia and the University of Chicago were interested in the rise of land animals. They focused on the gap between two primitive fossils, the mostly fish Panderichthys, from 385 million years ago, and the mostly land animal Acanthostega, from 365 million years ago.
In between, they reasoned, they should find a transitional form, a creature that lived in the late Devonian period and that shared attributes of both.
"This is a very large morphological gap," Jenkins said. "In order to work on this problem, we've got to go to back into the Devonian."
They knew of three major outcroppings of rocks from that time period. One, in Greenland, was being examined by European scientists. The second, in the Northeastern United States, was mostly buried by topsoil. The last outcropping was in the far north of the North American continent, along the rim of arctic Canada.
Using a 1991 geological survey map, they narrowed down their search area to about 600 square miles.
After that first disappointing season, they moved east to Ellesmere Island and focused their efforts around a place called Bird Fiord. They traveled in by small plane and helicopter and searched out likely rock outcroppings, finding some promising fossil fragments.
They returned in 2002 and again in 2004, finally tracking fossil fragments they had found to the source outcropping.
When they found Tiktaalik, however, researchers didn't know exactly what they had. The fossils were encased in rock and the researchers dared not try to expose them in the field. Instead, they carefully dug around the specimens to free them from the hillside. They encased them in plaster - which had difficulty drying in the damp environment - and shipped them back to the lab.
"If you try to expose them in the field, you will destroy them," Jenkins said. "Because you are a Neanderthal working with Neanderthal tools."
It was only months later, in March 2005, that they realized what they had found.
"We realized we had made the discovery of an extraordinary fish that had not been seen before," Jenkins said. "It is a fish, but it doesn't look like a fish."
With gills and scales, Tiktaalik was a fish, Jenkins said, but a strange one. It had an elongated snout and a flattened head that looked somewhat like a crocodile's. Unlike other fish whose heads attach directly to their bodies, Tiktaalik had a neck, allowing it to move its head independently. It had eyes on the top of its head, like any number of surface-dwelling creatures, from frogs to mudskippers to crocodiles. It had a stout skeleton, including reinforced ribs, perhaps for supporting itself outside of the water. It had wrist bones very similar to the earliest land animals and fins capable of bending and becoming a supportive limb on land.
"We have something that is at the very start of the development of the tetrapod," Jenkins said. "Here is a fin that is a fin and a supporting limb on land."
Judging from the rock in which it was found, Tiktaalik must have lived in shallow freshwater rivers 375 million years ago on a landmass that, at that time, was just north of the equator.
Though Tiktaalik has been widely referred to as a "missing link," Jenkins said he thinks the term is a bit of a misnomer and concurs with those who said its discovery just creates two new missing links, one on each side. Still, Jenkins acknowledged that Tiktaalik's discovery provides a stronger link between fishes and tetrapods, or four-legged land animals.
"This is just one piece of evidence of the great circle of life," Jenkins said.