Fossils provide direct evidence of an organism's existence. Frequently only the hardest tissues (bones and teeth) are preserved, but sometimes we get fossilized impressions of soft tissues.
We can use a variety of methods to assess how old fossils are and to glean information from the fossils about how the organism lived.
Humans are mammals and primates.
Mammals are characterized by homiothermy, heterodontism, lactation, internal gestation, and a set of unique brain structures.
Primates are characterized by a postorbital bar, or bony, enclosed eye socket; hands and feet capable of grasping; nails instead of claws on the ends of the digits; extensively overlapping visual fields; a large brain relative to body size; and long gestation and slow postnatal growth compared to maternal body size.
The earliest primates are thought to be derived from a group related to the Plesiadapis sometime in the late Cretaceous or early Paleocene.
There are three main hypotheses for the evolution of primates from Archontan stock; they center on arboreality; visual adaptation; and fruit, flower, and insect predation.
Three main primate groups show up in the fossils of the Eocene age: the Omomyoids, the Adapoids, and the Simiiform anthropoids.
The Oligocene fossils reveal a radiation of anthropoid forms and the colonization of South America by anthropoid primates.
By the Miocene, a new set of primates, the hominoids, began to radiate out of Africa. These primates exhibit a set of morphological characteristics that characterize the living apes.
The hominoids experienced a decrease in diversity by the terminal Miocene, at the same time that the number and diversity of nonhominoid anthropoid primates (monkeys) increased.
The best representations of primate evolution are those that reveal general patterns and trends over time.
