Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body Read Free Page A

the survey, Ted found a marvelous shoulder bone. We named its owner Hynerpeton, a name that translates from Greek as “little creeping animal from Hyner.” Hyner, Pennsylvania, is the nearest town. Hynerpeton had a very robust shoulder, which indicates a creature that likely had very powerful appendages. Unfortunately, we were never able to find the whole skeleton of the animal. The exposures were too limited. By? You guessed it: vegetation, houses, and shopping malls.
     

Along the roads in Pennsylvania, we were looking at an ancient river delta, much like the Amazon today. The state of Pennsylvania (bottom) with the Devonian topography mapped above it.
     
    After the discovery of Hynerpeton and other fossils from these rocks, Ted and I were champing at the bit for better-exposed rock. If our entire scientific enterprise was going to be based on recovering bits and pieces, then we could address only very limited questions. So we took a “textbook” approach, looking for well-exposed rocks of the right age and the right type in desert regions, meaning that we wouldn’t have made the biggest discovery of our careers if not for an introductory geology textbook.
    Originally we were looking at Alaska and the Yukon as potential venues for a new expedition, largely because of relevant discoveries made by other teams. We ended up getting into a bit of an argument/debate about some geological esoterica, and in the heat of the moment, one of us pulled the lucky geology textbook from a desk. While riffling through the pages to find out which one of us was right, we found a diagram. The diagram took our breath away; it showed everything we were looking for.
    The argument stopped, and planning for a new field expedition began.
    On the basis of previous discoveries made in slightly younger rocks, we believed that ancient freshwater streams were the best environment in which to begin our hunt. This diagram showed three areas with Devonian freshwater rocks, each with a river delta system. First, there is the east coast of Greenland. This is home to Jenny Clack’s fossil, a very early creature with limbs and one of the earliest known tetrapods. Then there is eastern North America, where we had already worked, home to Hynerpeton. And there is a third area, large and running east–west across the Canadian Arctic. There are no trees, dirt, or cities in the Arctic. The chances were good that rocks of the right age and type would be extremely well exposed.
    The Canadian Arctic exposures were well known, particularly to the Canadian geologists and paleobotanists who had already mapped them. In fact, Ashton Embry, the leader of the teams that did much of this work, had described the geology of the Devonian Canadian rocks as identical in many ways to the geology of Pennsylvania’s. Ted and I were ready to pack our bags the minute we read this phrase. The lessons we had learned on the highways of Pennsylvania could help us in the High Arctic of Canada.
    Remarkably, the Arctic rocks are even older than the fossil beds of Greenland and Pennsylvania. So the area perfectly fit all three of our criteria: age, type, and exposure. Even better, it was unknown to vertebrate paleontologists, and therefore un-prospected for fossils.
     

The map that started it all. This map of North America captures what we look for in a nutshell. The different kinds of shading reflect where Devonian age rocks, whether marine or freshwater, are exposed. Three areas that were once river deltas are labeled. Modified from figure 13.1, R. H. Dott and R. L. Batten, Evolution of the Earth (New York: McGraw-Hill, 1988). Reproduced with the permission of The McGraw-Hill Companies.
     
    Our new challenges were totally different from those we faced in Pennsylvania. Along the highways in Pennsylvania, we risked being hit by the trucks that whizzed by as we looked for fossils. In the Arctic we risked being eaten by polar bears, running out of food, or being marooned by bad