Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body by Neil Shubin

one of our blocks of rock, seen a fleck of bone, and prepared it with a needle under the microscope. None of us had known it in the field, but our expedition was a huge success. All because of Bill.
    What did I learn that summer? First, I learned to listen to Chuck and Bill. Second, I learned that many of the biggest discoveries happen in the hands of fossil preparators, not in the field. As it turned out, my biggest lessons about fieldwork were yet to come.
    The reptile Bill had found was a tritheledont, a creature known from South Africa as well as now from Nova Scotia. These were very rare, so we wanted to return to Nova Scotia the next summer to find more. I spent the whole winter tense with anticipation. If I could have chipped through the winter ice to find fossils, I would have done it.
    In the summer of 1985, we returned to the site where we had found the tritheledont. The fossil bed was just at beach level, where a little piece of the cliff had fallen off several years before. We had to time our daily visit just so: the site was inaccessible at high tide because the water came up too high around a point we had to navigate. I’ll never forget that first day of excitement when we rounded the point to find our little patch of bright orange rock. The experience was memorable for what was missing: most of the area we had worked the year before. It had weathered away the previous winter. Our lovely fossil site, containing beautiful tritheledonts, was gone with the tides.
    The good news, if you could call it that, was that there was a little more orange sandstone to scan along the beach. Most of the beach, in particular the point we had to go around each morning, was made up of basalt from a 200-million-year-old lava flow. We were positive no fossils could be found there, for it is virtually axiomatic that these rocks, which were once super hot, would never preserve fossil bone. We spent five or more days timing our visits to the sites by the tides, pawing away at the orange sandstones beyond it, and finding absolutely nothing.
    Our breakthrough came when the president of the local Lions Club came by our cabin one night looking for judges for the local beauty contest, to crown Parrsboro’s Miss Old Home Week. The town always relied on visitors for this onerous task, because internecine passions typically run high during the event. The usual judges, an elderly couple from Quebec, were not visiting this year, and the crew and I were invited to substitute.
    But in judging the beauty contest and arguing over its conclusion, we stayed up way too late, forgot about the next morning’s tides, and ended up trapped around a bend in the basalt cliffs. For about two hours, we were stuck on a little promontory about fifty feet wide. The rock was volcanic and not the type one would ever choose to search for fossils. We skipped stones until we got bored, then we looked at the rocks: maybe we’d find interesting crystals or minerals. Bill disappeared around a corner, and I looked at some of the basalt behind us. After about fifteen minutes I heard my name. I’ll never forget Bill’s understated tone: “Uh, Neil, you might want to come over here.” As I rounded the corner, I saw the excitement in Bill’s eyes. Then I saw the rocks at his feet. Sticking out of the rocks were small white fragments. Fossil bones, thousands of them.
    This was exactly what we were looking for, a site with small bones. It turned out that the volcanic rocks were not entirely volcanic: slivers of sandstone cut through the cliff. The rocks had been produced by an ancient mudflow associated with a volcanic eruption. The fossils were stuck in the ancient muds.
    We brought tons of these rocks home. Inside were more tritheledonts, some primitive crocodiles, and other lizard-like reptiles. The tritheledonts were the gems, of course, because they showed that some kinds of reptiles already displayed our mammalian kind of chewing.
    Early mammals, such as those