archaeology unit 10

the first Bipeds

hominids

the family that includes the great apes (orangutans, gorillas, chimpanzees, and bonobos) and humans

hominins

the tribe that includes humans and their fossil ancestors. Hominins began to appear in the African fossil record around 7-6 mya.

the Pliocene epoch

The important geological period in which the steady movement of the African and European tectonic plates occasioned a crash of the two continents in the Mediterranean Sea.

bipedalism

considered to be the fundamental behaviour defining hominins because it predates by millions of years other traits associated with the human family (such as the making of tools and the development of language) and it is probably at the origin of some of these attributes.

foramen magnum

the opening in the skull to admit the spinal cord that connects the brain with the rest of the body- defines the position of the body in relation to the head and, therefore, it may indicate whether the creature was bipedal or not.

foramen magnum, the pelvis, the vertebral column, the bicondylar angle, The foot.

some of the number of anatomical traits indicating bipedal locomotion

Charles Darwin’s hunting hypothesis

A theory explaining the origins of bipedalism which says that bipedalism had freed the hands for creating and, more importantly, for using tools and weapons. This explained why apes have big canines (that they need for hunting and defence) and humans have not. One of the main problems with this theory is that scientists have documented tool use in the fossil record long after the appearance of bipedalism. In first, while bipedalism was first adopted around 6/7 mya, the first tools made by humans date to about 2.6 mya. In other words, it now seems doubtful that tool use was at the origins of bipedalism.

Peter Rodman and Henry McHenry’s Patchy Forest Hypothesis

A theory explaining the origins of bipedalism which says bipedalism gave an energetic advantage on the Miocene hominoid ancestors of the Hominidae in certain habitats. In particular, they suggest that bipedalism first arose in those areas in which the tropical forest was becoming patchy. In an environment in which forest became fragmented and food became more disperse, bipedalism gave an advantage to earl hominins because it freed their hands to pick up food. In other words, “bipedalism might therefore be an energy-saving adaptation for moving between forest patches”^.

Owen Lovejoy’s Provisioning Hypothesis

A theory for explaining the origins of bipedalism that says that bipedalism emerged as a strategy adopted by the monogamous father to assure the survival of the mother and the young by providing food. In other words, bipedalism arose because the male needed free hands in order to provide both food and protection to the mother and the offspring.

Peter Wheeler’s Thermoregulatory Model

A theory for explaining the origins of bipedalism that says that because hominins ventured out of the forest more they needed to evolve to reduce heat stress associated with being out in the savanna, which standing upright encourages.

Yves Coppens’ Theory of ‘Tectonic Crisis’

A theory explaining the origins of bipedalism that suggests when the tectonic crisis occurred the land was separated into forest and savanna and so where hominins and the evolution of upright standing occurred because walking upright provided hominins with a better vision in the open-country landscapes of East African.

Kevin Hunt’s Theory of Ecology and Functional Morphology

A theory explaining the origins of bipedalism which says that bipedalism was favoured because it allowed more efficient harvesting of fruit from the small trees that predominate in the African savannah. This researcher realized realized that while chimpanzees only exceptionally walk upright, they often stand bipedally in order to harvest fruit from small trees.

Daniel Lieberman’s Theory on Human Locomotion and Heat Loss

a theory explaining the origins of bipedalism that says that this evolution occurred because upright walking requires much less energy and early hominins had to start walking farther and they needed to evolve so that they didn’t experience as much overheating and physical exertion to aid in survival.

pre-australopithecines

refer to a number of fossils dated during the period between ca. 7 and 4 mya. They represent the first ancestors of the lineage leading to modern humans. These fossils had a number of primitive characteristics and, in general, they were more apelike than humanlike. However, some anthropologists think that these fossils were bipedal and, for this reason, they are often included in the human family. The most important fossil species from this period are Sahelanthropus tchadensis, Orrorin tugenensis and Ardipithecus.

Sahelanthropus tchadensis

A hominin fossil whose traits consist of Very low forehead

• The brain was similar in size to that of modern chimpanzees (350 cc).

• Massive browridge.

• Highly projecting face.

• The foramen magnum is located on the bottom of the skull. This seems to indicate that this fossil walked upright.

Orrorin tugenensis

These fossils include parts of thigh and arm bones, finger bones, two mandibles and several teeth that have been securely dated to 6 mya. Particularly important is the proximal (upper) portion of the femur, which has a long neck that is very similar to the one that we can see in modern people.

Ardipithecus

a genus discovered from a fossil discovery. This genus includes Ardipithecus kadabba and Ardipithecus ramidus dating to about 6/4.5 mya. These hominins were found in a forested ecological area, something that seems to indicate that not all of the early hominins evolved in the open grasslands. Moreover, several traits indicate that Ardipithecus ramidus was bipedal. For instance, the foramen magnum is in a forward position. At the same time, foot bones indicate that the big toe is opposable, as in apes. These anatomical traits seem to indicate that Ardipithecus was adapted to life in trees and to life on the ground.

Australopithecus

About 4 mya, the hominin lineage proliferated and in the next 2 million years several species of hominins cohabited in Africa. Today, all these species are usually considered to belong to the same genus. The name for this group of fossils was coined in 1924 when Raymond Dart discovered the so-called ‘Taung child’ in South Africa. Since then, numerous fossils attributed to this genus have been found in the African Continent.

Australopithecus anamensis

One of the two oldest known species of Australopithecus, came from East Africa. Some jaw and limb bones corresponding to this species have been dated to between 4.2- 3.8 mya. In short, these hominins had large, broad molars with thick enamel and smaller canines. The limb bone fragments indicate bipedalism.

Australopithecus afarensis

one of the two oldest known species of Australopithecus that came from East Africa. well-known from different specimens found at several sites in Africa. The most spectacular finds corresponding to this species (Lucy) were discovered by Donald Johanson in the early 1970s.

robust australopithecines

one of the two categories of late Australopithecines. The main morphological features of the robust australopithecines are related to powerful masticatory stresses. For instance, the most typical trait on most robust crania is the presence of a sagittal crest indicating the large size of the temporalis muscle in relation to the braincase. Moreover, they huge had enormous post-canine teeth generated by large chewing stresses. Similarly, they had huge mandibles to accommodate their massive post-canine teeth. These traits seem to indicate that robust forms adapted to tough vegetarian diets that included roots, seeds, and bulbs. Australopithecus robustus and Zinjanthropus boisei are generally considered as paradigmatic examples of this category of Australopithecines.

gracile australopithecines

one of the two categories of late Australopithecines. The morphological patterns of which consist of the postcanine teeth are relatively small, facial prognathism is more evident, and the forehead is higher than in the robust form. These traits indicate lower chewing stresses in the gracile species probably related to a lighter diet. Australopithecus africanus, Australopithecus garhi and Australopithecus sediba are generally considered examples of this category of Australopithecines. Australopithecus africanus was first identified by Raymond Dart in 1924 when he discovered the skull of an immature, small-brained creature. Dart’s fossil is known as the ‘Taung child’. Australopithecus garhi was discovered in the Awash Valley of Ethiopia in 1999. The discovery included a number of postcranial bones and the partial skeleton of one individual that have been securely dated to 2.5 mya.

from the late Miocene through the Pliocene and into the Pleistocene (about 6-1 mya)

When did early hominins begin to evolve?

7 - 4 mya

What is the chronology associated to pre-australopithecines?

4 - 2.5 mya

What is the chronology associated to early australopithecines?

2.5 - 1 mya

What is the chronology associated to late australopithecines?