The Emergence of Primates
Paleontologists have found the fossils of early primates in North America, Europe, Africa, and Asia. The fossils are usually found within layers of sedimentary rock, rock formed from sediments of mud, clay, silt, or sand deposited over long spans of time on the bottom of rivers, lakes, swamps, and oceans. In general, the lower a rock layer is in a sequence of layers, the older it is. Layers that are as old as the first primates could be quite deep, but they have often been exposed through natural processes, including uplift, in which one section of the Earth's crust runs into another and gradually pushes it up, and weathering by water and winds.
To extract fossils from ancient rock, paleontologists use many methods. Frequently, they stumble across partially exposed bones and remove the surrounding rock with a hammer and chisel or, for more delicate work, an icepick. When they come across layers of loose sand or mud, they brush, shovel, and sift their way through, looking for bones and teeth. In some cases paleontologists break open chunks of rock to see if there are bones inside. To better understand the fossils that they discover, researchers note the depth of the rock layer in which the fossils were found, the other fossils found in that layer, and the types of minerals and sediments in the layer. This helps them determine what kind of environments the primates inhabited when they were alive.
Discoveries of primate fossils have mostly been limited to teeth, jaw bones, pieces of skulls, and a few scattered fragments from other parts of the body. Teeth, which contain apatite, a hard and durable mineral that makes them tougher than other types of skeletal remains, account for the greatest number of early-primate fossils.
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