Читать книгу Anthropology For Dummies - Cameron M. Smith - Страница 71

The earliest proto-primates have been traced from fossils of the Paleocene epoch some 65 million years ago; most anthropologists agree that the Primate order was well underway by 60 million years ago. The number 65 million may ring a bell as the time of the extinction of the dinosaurs, and the rise of primates is related to the demise of the dinosaurs. Early mammals, from which the primates evolved, appear somewhat earlier, but when the dinosaurs became extinct, the way opened up for other life forms to flourish. Many more mammals show up after 65 million years ago, and among them are the first primates.

Many fossils of early primates are found in Europe and North America, which is a little jarring, because there aren’t natural primate populations in these areas — well, except for humans! — today. This is because at this time, the continents were differently arranged than they are today.

In addition to the fossil evidence for primate origins, today we have a tremendous paleogenomic (ancient DNA) record. This evidence largely corroborates what the fossils have been telling us for over a century. It also provides fascinating new details, such as a detailed chronology of the evolution of different lineages. The DNA record, for example, tells us that the New World primates (those of South and Central America) split from the Old World primates about 35 million years ago, which ties up nicely with geological evidence for continental drift around this time.

The fossils of the earliest primates show two main features:

 Small body size, averaging roughly 150 to 3,000 grams, or about 1⁄3 pound to about 6 pounds

 Teeth indicating an insectivorous diet (one specializing in insects)

So our earliest primate relatives were small, insect-eating mammals, in many ways physically similar to squirrels. You can see a reconstruction of one of these first primates in Figure 4-1. Skeletal analysis suggests that these early primates were arboreal (lived in trees) and that’s very common in the living primates.

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FIGURE 4-1: An early primate. My reconstruction is based on the fossil evidence, which indicates a squirrel-like creature adapted for an arboreal (tree-dwelling) life.

Most of the characteristics of the early primates are studied from fossils of their teeth and skulls (and a few limb bones). Bone fossilization is the process by which minerals slowly replace the organic content of the bones of a dead animal, resulting in a very detailed stone replica of the original bone. Fossils can be so detailed that they show scratches (on the teeth, for example, from chewing) under a microscope.