How to Build a Dinosaur by Jack Horner Read Free Book Online

Formation and seeing the coal that marks the end of the Cretaceous. All around you are elements of a fossil snapshot of the world just before a catastrophic event. Prospecting for fossils doesn’t just produce the discovery of new species. Each fossil is a pixel in the increasingly detailed image we have of the moment before the extinction. That is the time frame you occupy in Garfield County: the moment before the end.
    Or you can occupy the present, at least the present of Garfield County, which is a bit of a dislocation from, say, the present of Berkeley, or New York, or Washington. Fortunately, the ageless feeling of the rangeland in Garfield, the sparse human population, the quiet at night and the wide open sky provide a cushion against the gap in time, so that it does not feel so odd to be straddling the eons. But one thing that the rocks of Garfield County do not offer is any sense of what happened between then and now. Life did not cease on this patch of the planet’s surface with the extinction. Sixty-five percent of species survived, some prospered, and many new ones emerged. But no record of these events was preserved here. The deposits continue for a few more million years after the K/T boundary. Some of that time is preserved in deposits in and around Jordan that look much like the Hell Creek deposits except that they are tan rather than gray, there is more coal, and it seems to have been swampier than before the extinction.
    The Paleocene lasted for another ten million years, and some of that can be seen in Garfield County badlands. But not much later. Life continued in the area, but we have no sedimentary rock from that time in that location. The planet’s surface is a patchwork of different time exposures, like a canvas painted over many times, with different works showing through at different spots where the paint is thicker or more has been scraped off by curious art historians.
    We have to turn to other fossil records, of which there are many, for an idea of how this part of the planet made it from then to now. If only for the sake of context, it is worth stopping to fill in a few of the blanks.

SINCE THE DINOSAURS
    What has happened to North America since that time? The answer is: almost everything. The continent, and the world, went through geological and climactic upheavals. Mammals began to radiate into forms that seem outlandish today. In their range of shape and behavior they challenge the dinosaurs, although the dinosaurs get most of the press, perhaps because there are so many mammals around now, such as humans.
    If one is tempted to think of the mammals as a poor sequel to the dinosaurs, it’s worth remembering that they lived through the entire age of the dinosaurs as well. What happened after the extinction of the nonavian dinosaurs was simply that they became the dominant land animals, as they are today. The impact of the meteorite was a crisis, but a manageable one for life on the planet. As for the rock we all live on, the Rockies continued to thrust upward, other mountain ranges of the West emerged, seas disappeared and reappeared in the center of North America.
    In what is now the High Plains of eastern Montana, the conditions were junglelike as mammals began to radiate. The emergence of these creatures and their radiation into so many forms is as vivid an indication of how evolution proceeds as was the era of the dinosaurs, or the evolution of birds, which coincided with the mammalian explosion. Every shape and size emerged among mammals, in configurations that we are familiar with—extremely large herbivores, like the uintatheres; predators with flesh-cutting teeth; small mouse- and shrew-like animals; the swift (deer- and antelope-like creatures); and the slow (great sloths).
    All of these widely divergent creatures were variations on the standard mammalian model. All were furry tetrapods with five-digit hands and feet, hearts, lungs, and brains. Those brains were protected by the