Introduction to Paleoanthropology

HOMINOID, HOMINID, HUMAN

The traditional view has been to recognize three families of hominoid: the Hylobatidae (Asian lesser apes: gibbons and siamangs), the Pongidae, and the Hominidae.

• The Pongidae include the African great apes, including gorillas, chimpanzees, and the Asian orangutan;
• The Hominidae include living humans and typically fossil apes that possess a suite of characteristics such as bipedalism, reduced canine size, and increasing brain size (e.g., australopithecines).

The emergence of hominoids

Hominoids are Late Miocene (15-5 million years ago) primates that share a small number of postcranial features with living apes and humans:

• no tail;
• pelvis lacks bony expansion;
• elbow similar to that of modern apes;
• somewhat larger brains in relationship to body size than similarly sized monkeys.

When is a hominoid also a hominid?

When we say that Sahelanthropus tchadensis is the earliest hominid, we mean that it is the oldest fossil that is classified with humans in the family Hominidae. The rationale for including Sahelanthropus tchadensis in the Hominidae is based on similarities in shared derived characters that distinguish humans from other living primates.

There are three categories of traits that separate hominids from contemporary apes:

• bipedalism;
• much larger brain in relation to body size;
• dentition and musculature.

To be classified as a hominid, a Late Miocene primate (hominoid) must display at least some of these characteristics. Sahelanthropus tchadensis is bipedal, and shares many dental features with modern humans. However, the brain of Sahelanthropus tchadensis was no bigger than that of contemporary chimpanzees. As a consequence, this fossil is included in the same family (Hominidae) as modern humans, but not in the same genus.

Traits defining early Homo

Early Homo (e.g., Homo habilis) is distinctly different from any of the earliest hominids, including the australopithecines, and similar to us in the following ways:

• brain size is substantially bigger than that of any of the earliest hominids, including the australopithecines;
• teeth are smaller, enamel thinner, and the dental arcade is more parabolic than is found in the earliest hominids, including the australopithecines;
• skulls are more rounded; the face is smaller and protrudes less, and the jaw muscles are reduced compared with earliest hominids, including the australopithecines.