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C h a p t e r 1 3

... w

e are all united by our past, that we all have a common history and though we may be vastly different, our origins all lead back to the crucible of human evolution that is Africa. [Lucy’s] announcing: “You are all my descendants and regardless of who we are, we are all, in fact today, Africans.”

—Donald C. Johanson1

Chapter Outline

Discoveries of the Early Hominins The Early Hominins of South Africa The Fossils of Olduvai Gorge The Fossils of the Lake Turkana Basin The Fossils of the Afar

The Laetoli Footprints The Fossils of Chad Drawing a Family Tree Summary

Early Hominins: Interpretations of the Evidence

Australopithecines as Erect Bipeds Early Hominin Tool Use

Early Hominin Dentition The Early Hominin Brain The Early Hominin Skull Ecology and the Early Hominins Summary

After Reading This Chapter, You Should Be Able to Answer These Questions: 1. What contribution did the early hominin fi nds in South Africa by Raymond Dart,

Robert Broom, and others make to our understanding of hominin evolution? How would you describe these South African hominins?

2. What are the important east African sites? What kinds of early hominins were found there, and who found them?

3. In what ways did the early hominins from South Africa differ from those from east Africa?

4. Have early hominins been found anyplace else other than South Africa and east Africa? 5. What do the hominin footprints at Laetoli tell us about the hominins that made them? 6. What evidence is there that Australopithecus and Paranthropus were erect bipeds?

What might have been some of the adaptive advantages of bipedalism over quadru-pedalism for the evolving hominins?

7. What evidence is there that the early hominins used tools?

8. In what ways does the dentition of Australopithecus and Paranthropus differ from that of earlier hominins, modern apes, and the genus Homo?

9. What where some of the changes that evolved in the brains of Australopithecus and Paranthropus in comparison to earlier forms?

10. What types of habitats did Australopithecus and Paranthropus occupy, and how might those habitats have infl uenced their behavior?

See the Online Learning Center for a chapter summary, chapter outline, and learning objectives.

The Early Hominins

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1 Quoted in L. E. Bohn, “Q&A: ‘Lucy’ Discoverer Donald C. Johanson,” Time (March 4, 2009)—www.time.com/ time/health/article/0,8599,1882969,00.html

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The 1977 television miniseries Roots was the most-watched series of its time. People seem to be fascinated with tracing their line of descent back through several hundred years of time. Many are drawn to physical anthropology by their curiosity about even deeper roots. The exploration of the origins of humanity raises many interesting questions: With what other contemporary animals do we have a close common ancestry? Why did the hominin line go off in the direction it did? At what point should we use the word human to describe our ancestors? What made those ancestors human? What makes us unique?

In Chapter 12 we explored the early hominin fossils from the Late Miocene and Early Pliocene, although the hominin status of some of those fi nds is still in question. By 4 million years ago the relatively well-known genus Australopithecus appears on the scene. Around 2½ million years ago we see the appearance of the genus Homo, which coexists until about 1 million years ago with the genus Paranthropus. Both of these genera very likely arose from a species of Australopithecus. The two genera Australo pithecus and Paranthropus (along with Kenyanthropus) are frequently referred to as the australopithecines.

We begin the exploration of the australopithecines with the history of discoveries, many of which have captured the imagination of the world. Many of the sites and the names of the associated paleontologists are well known to subscribers to National Geographic and viewers of Nova and the Discovery Channel. Several have even appeared on the cover of Time and Newsweek. The section that follows the history of discovery discusses the anatomy and signifi cance of those fossils.

DISCOVERIES OF THE EARLY HOMININS

The fascinating story of the discovery of the australopithecines begins in late 1924 in South Africa. Like many important early discoveries, it was not accepted immediately because it contradicted many cherished hypotheses held by the prominent paleontologists of the time. However, beginning in 1936, the eventual discovery of hundreds of australopithecine fossils established several australopithecine species as important elements in the story of hominin evolution. All the fossils have been found in Africa. It was not until the evolution of the genus Homo that the hominins moved out of Africa and into other parts of the world. That story will be covered in Chapters 14 and 15.

The Early Hominins of South Africa

Much of South Africa rests on a limestone plateau. Limestone is often riddled with caves, and many of the more ancient ones have become completely fi lled in with debris. The 1920s was a period of tremendous growth in South Africa, and the need for limestone, a con-stituent of cement, brought about an increase in quarrying activities. The blasting activities of workers in limestone quarries often expose the ancient cave fi lls. The material that fi lls these caves is bone breccia, which consists of masses of bone that have been cemented together with the calcium carbonate that has dissolved out of the limestone.

In 1924, fossil material from the quarry at Taung was delivered to Raymond A. Dart (1893–1988) of the University of Witwatersrand in Johannesburg, South Africa (Figure 13.1). Embedded within the bone breccia was a small skull. Dart spent 73 days removing the limestone matrix from the skull; he spent four years separating the mandible from the rest of the skull. The fossil that emerged from the limestone matrix consisted of an almost complete mandible, a facial skeleton, and a natural endocranial cast (Figure 13.2). The jaws contained a set of decid-uous teeth along with the fi rst permanent molar. Dart called the fi nd the “Taung Baby”; he named it “Taung” after the quarry in which it was found, and he called it “baby” because it was a child.

Dart published his fi nd on February 7, 1925.2 He named the skull Australopithecus africanus, from Australo, meaning “southern,” and pithecus, meaning “ape.” Dart saw in

australopithecines

Members of the genera Australopithecus and Paranthropus, who lived in Africa approximately 4 to 1 million years ago.

bone breccia Cave fi ll

consisting of masses of bone cemented together with calcium carbonate that has dissolved out of limestone.

2 R. A. Dart, “Australopithecus africanus, the Man-Ape of South Africa,” Nature 115 (1925), p. 195; see also R. A. Dart, “Recollections of a Reluctant Anthropologist,” Journal of Human Evolution 2 (1973), pp. 417–427.

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Fossils are given designations that include an abbreviation for the site (and sometimes the museum housing the specimens) and an acquisition number. The latter is usually given to fossils in the order in which they are discovered. The site abbreviations used in this chapter are AL (Afar Locality), BOU-VP (Bouri Vertebrate Paleontology), DIK (Dikika), DNH (Drimolan), ER (East Rudolf, the

Box 13-1

former name for East Turkana), KNM (Kenya National Museums), KP (Kanapoi), KT (Koro Toro), LH (Laetoli Hominid), MH (Malapa Hominin), MLD (Makapansgat Lime Deposit), OH (Olduvai Hominid), OL (Olorgesailie), SK (Swartkrans), Sts (Sterkfontein), Stw (Sterkforten West Pit), and WT (West Turkana).

Figure 13.1 Distribution of Early Hominins in Africa See Box 13-1 for the meaning of the abbrevia-tions. (a) Au. afarensis, reconstructed skull, Hadar; (b) Au. afarensis, DIK-1-1, Dikika; (c) Au. garhi, BOU-VP-12/130, Middle Awash; (d) P. boisei, KNM-ER-406, Koobi Fora; (e) P. boisei, OH 5, Olduvai Gorge; (f) Au. sediba, MH1, Malapa; (g) P. robustus, DNH 7, Drimolen; (h) P. robustus, SK 48, Swartkrans; (i) Au. africanus, Taung; (j) Au. africanus, Sts 5, Sterkfontein; (k) Au. afarensis, footprints, Laetoli; (l) Au. anamensis, KNM-KP-29281, Kanapoi; (m) P. aethiopicus, WT 17000, Lomekwi; (n) K. platyops, WT 40000, Lomekwi;

(o) Au. bahrelghazalia, KT 12/H1, Bahr el Ghazal. (i) (j) (h) (e) (m) (n) (l) (k) (g) (d) (a) (o) (c) (b) (f)

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this skull the characteristics of a primitive hominin, the most primitive of humankind’s known ancestors. Dart based his opinion on the homininlike structure of the teeth, the nature of the endocranial cast, and the forward position of the foramen magnum, which was consistent with erect bipedalism.

Other paleoanthropologists, however, were not convinced. Some noted the diffi culties of making valid comparisons using an incomplete juvenile skull; some paleoanthropolo-gists argued that the skull showed close affi liations to the skulls of apes. Others were convinced that the earliest hominins would be characterized by apelike features associ-ated with a large brain, which was precisely what was seen in the later-discredited Piltdown skull (Chapter 11). Yet Dart persisted in his contention that the Taung baby was a bipedal hominin; the years have proved him correct.

Australopithecus africanus and Paranthropus robustus In his day, Dart’s interpretation of Australopithecus africanus was not accepted by most paleoanthropologists and he had very little support for his ideas. One exception was the Scottish physician and paleontologist Robert Broom (1866–1951). After retiring from his medical practice at age 68, Broom began an investigation of three caves in the Sterkfontein Valley. He excavated the fi rst cave, Sterkfontein, between 1936 and 1939 and almost immediately uncovered the fi rst adult spec-imens of Au. africanus (Figure 13.3). In 1938, Broom excavated at the site of Kromdraai. There he found a specimen that, unlike Au. africanus, possessed a sagittal crest on the top of the cranium, a large mandible, and very large premolars and molars (Figure 13.4). He placed that fossil in the new species Paranthropus robustus. Paranthropus means “parallel to man.” He recovered additional specimens at the site of Swartkrans. Stratigraphically, Au. africanus is older than P. robustus.

C. K. Brain, who began his excavations in 1965, has reconstructed what the cave at Swartkrans was like when the fossils were deposited (Figure 13.5). At that time, the cave was an underground cavern connected to the surface by a vertical shaft. Because of a concentration of moisture in the relatively treeless region, trees were found in the region of the shaft. Leopards are known to drag their prey into trees, where the carcass is rela-tively safe from scavengers and other carnivores. For this reason, the remains of the ani-mals of prey would have found their way down the shaft and into the cave. This accounts for the relative lack of postcranial remains, which would have been destroyed to a large extent by chewing. Au. africanus and P. robustus would have been among the leopard’s prey (Figure 13.6).

Figure 13.2 Australopithecus africanus The mandibular fragment, facial skeleton, and natural endocranial cast of the “Taung Baby” found at Taung, South Africa, in 1924.

See the Online Learning Center for an Internet Activity on Australopithecus africanus.

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Figure 13.3 Australopithecus africanus Sts 5, from Sterkfontein, South Africa.

The dating of the South African sites has been diffi cult because of the lack of volcanic material. Most estimates are based on a comparison of the remains of fossil animals with those of similar animals at other dated sites. The material at Sterkfontein covers a vast period of time. It is divided into fi ve stratigraphic layers that are named Member 1 through Member 5. The most recent, Member 5, contains fossils of Homo and Paranthropus robustus; Member 4 contains fossils of Australopithecus africanus. The oldest hominin-bearing layer, Member 2, contains fossils of Australopithecus, but the species has not

Figure 13.4 Paranthropus robustus SK 48, from Swartkrans, South Africa.

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been determined. Recent dating using the radioactive materials aluminum 26 and beryl-lium 10 have yielded a date of about 4 million years for Member 2, much older than has previously been thought.

Not all fossils are discovered in the ground, however. Paleoanthropologists announced in 1994 that they had recovered four bones of a left foot from a box of mammalian bones that originally had been excavated in 1980 at the site of Sterkfontein. The fossils are dated between 3.5 and 3.0 million B.P. These bones (Stw 573), nicknamed “Little Foot,” fi t together to form an arch that extends from the heel of

the foot to the beginning of the big toe. Workers then returned to the cave in an attempt to recover additional bones. In 1997, they found eight more foot and lower leg bones. Further work uncovered leg and arm bones as well as a skull. This skeleton is among the oldest austra-lopithecine fossils, dating from around 4 million B.P., which is contemporary with the oldest australopithecine material in east Africa belonging to the species Austra-lopithecus anamensis. It is also one of the few fi nds in which the skulls have been found in association with postcranial material.

The site of Drimolen, discovered in 1992 just north of Sterkfontein, had yielded 92 hominin fossils by 2009. They are placed into the species Paranthropus robustus, although a few specimens are thought to belong to a spe-cies of Homo. This is not surprising since we know that Paranthropus and Homo were contemporary. Perhaps the most important fossil is DNH 7, which is the most com-plete australopithecine skull that has been recovered to date. It is relatively small, lacks a sagittal crest, and is thought to be a female. Nonhuman bones found at Drimolen show signs of alteration indicating they were used as tools. 0 20 40 12 6 0

Talus cone apex

Catchment area

Dolomite Present surface

Reconstructed rock shelter and shaft Reconstructed surface ft. m.

Figure 13.5 Reconstruction of the Cave at Swartkrans Diagrammatic section through the Swartkrans hillside.

The upper reconstructed part has been removed by erosion since the accumulation of the fossil deposit.

Figure 13.6 Evidence of Leopard Predation This photo-graph shows part of the skull (parietal) of a juvenile hominin from Swartkrans (SK 54). The two holes in the skull match the lower canines of a leopard. The fossil leopard mandible (SK 349) comes from the same deposit.

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Figure 13.7 Australopithecus sediba MH1 from Malapa, South Africa.

Australopithecus sediba A collection of fossil bones was discovered in 2008 by Matthew Berger, the then 9-year-old son of Lee Berger of the University of the Witwatersrand, South Africa. They were found at the site of Malapa, located some 15 kilometers northeast of the Sterkfontein Valley. The new fossils include two partial skeletons. MH1 (Malapa Hominin 1) consists of parts of the cranium, mandible, and postcranial skeleton of a juvenile male with erupted second molars, thought to have died between 12 and 13 years of age. MH2 is an adult female and is represented by teeth, part of a mandible, and a partial postcranial skeleton (Figure 13.7). There are two additional individuals represented, one of which is an infant. They have yet to be analyzed.

Malapa is a limestone cave. Perhaps the now-fossilized individuals fell into the opening reaching for water. Eventually the top of the cave collapsed on the remains. As a result, the stratigraphy of Malapa is very complex. The dating of the South African cave sites has always been diffi cult, in part because of the absence of volcanic material. However, uranium-lead (U-Pb) dating can be used to date fl owstones, associ-ated with limestone caves. Paleomagnetic dating has also proven very useful. Using these two techniques, the fossils have now been quite accurately dated at 1.977 million years old.

The skeletons show a mixture of features that characterize both Australopithecus and Homo. The cranial capacity of MH1 has been estimated at 420 cubic centimeters, within the australopithecine range. Material found on the inner surface of the cranium provides a natural endocranial cast. Although showing a basic australopithecine pattern, the cast does suggest some expanded regions of the brain associated with the genus Homo.

The Malapa hominin fossils provide us with two partial pelvises. They possess a mosaic of australopithecine and Homo features. While undoubtedly an erect biped, it may have moved around in a way that was different from that seen in later hominins. Analysis of the hand and foot show a similar mosaic of features, combining australo-pithecine features with features found in the later Homo species. The structure of the hand suggests some degree of arboreal behavior, but the hands are believed to have been capable of the use and manufacture of tools, although no evidence of tools has

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been found. The investigators have placed the skeletons into a new australopithecine species, Australopithecus sediba. Sediba means “fountain” or “wellspring” in the Sotho language.

The Fossils of Olduvai Gorge

Olduvai Gorge, in east Africa, is a 25-kilometer- (151

2-mile-) long canyon cut into the

Serengeti Plain of Tanzania (Figure 13.8). The sedimentary beds, some 100 meters (328 feet) thick, have yielded bones of ancient hominins along with the tools that they made, as well as the remains of the animals they ate.

Geologically, the sequence of sedimentary layers at Olduvai is divided into a series of beds. Bed I and the lower part of Bed II show a continuous sequence of sediments that were deposited when a large lake existed on what is now part of the Serengeti Plain. Bed I and Lower Bed II span the time from 1.9 to 1.5 million B.P. (Figure 13.9).

Hominin sites are often located at what were once lake margins or stream banks. These areas provided the early hominins with a source of water as well as a concentration of animal food. In addition, fossilization more frequently occurs in these habitats as opposed to the savanna grasslands and tropical forests. The oldest hominin site in Olduvai Gorge is located just above a layer of basalt with a potassium-argon date of 1.9 million B.P. Hominin material also has been recovered from Middle and Upper Bed II, dated between 1.5 and 1.1 million B.P. During that time, the freshwater lake became smaller, and much of the landscape became a dry grassland.

The story of Olduvai Gorge is the story of Louis and Mary Leakey. Louis Leakey was predisposed to think of the early South African hominins as a side branch of the hominin line that played no role in the evolution of modern humans. He saw the genus Homo as a lineage of great antiquity whose major features were a large brain and the ability to manufacture tools.

Figure 13.8 Olduvai Gorge, Tanzania

See the Online Learning Center for an Internet Activity on Olduvai Gorge and the Leakeys.

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Although he and Mary later went on to make several important discoveries of early Homo, their earliest signifi cant fi nd was a hominin that did not belong to the genus Homo.

Louis Leakey began his work in Olduvai in 1931; Mary arrived on the scene in 1935. Although the discoveries of animal fossils and important archaeological material were made early, the fi rst signifi cant hominin fi nd did not appear until 1959. In that year, Mary Leakey found the cranium of a hominin, designated OH 5 (nicknamed “Nutcracker Man”), who lived at Olduvai Gorge around 1.75 million B.P. (Figure 13.10). This date was the fi rst to be determined by the then-new potassium-argon dating technique. At a time when most anthropologists considered hominin evolution to be confi ned to the last 1 million years, this new information almost doubled the time span estimated for human evolution. The fi nd originally was named Zinjanthropus boisei, after Zinj, an ancient name for east Africa, and in honor of Charles Boise, a London businessman who fi nanced the excavations at Olduvai Gorge in the 1950s. It is now designated Paranthropus boisei.

See the Online Learning Center for an Internet Activity on Paranthropus boisei. Age (million years) Gadeb Hadar Middle Awash Laetoli Bed II Bed III Bed IV Olduvai 0.5 1.0 Silbo Gele Lower Nariokotome Chari (L) Black Pumice (J-7) Malbe (H-4) KBS (H-2) Tuff G Tuff B-10 Ninikaa Toroto Lomogol Upper Unit Base, Laetoli Laetoli Tuff 7 Laetoli Tuff 8 Naibadad Beds Naabi Ignimbrite Bed I Lava Tuff IF Tuff IB Ogol Lavas Sidi Hakoma Kada Hadar BKT-2 Ignimbrite Adaba Wargolo Wargolo Moiti Moiti Cindery Karsa Basalt Topermawi Lokochot Tulu Bor Lokalalei (D) Burgi Kokiselei (E) Kalochoro (F) Morutot (J-4) 2.0 3.0 4.0 0.74 ± 0.01 1.25 ± 0.02 1.48 2.35 1.33 ± 0.03 1.39 ± 0.02 1.87 ± 0.02 2.03 ± 0.01 2.26 ± 0.06 2.41 ± 0.12 3.56 ± 0.20 4.32 ± 0.06 3.76 ± 0.03 3.49 ± 0.12 3.46 ± 0.12 1.80 ± 0.01 1.75 ± 0.01 v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v 1.65 ± 0.03 1.86 ± 0.02 1.88 ± 0.02 2.52 ± 0.05 2.68 ± 0.03 2.95 ± 0.05 3.06 ± 0.05 3.32 ± 0.02 3.76 ± 0.04 4.35 ± 0.05 ≤4.10 ± 0.07 2.34 ± 0.04 2.88 ± 0.08 3.80 ± 0.05 2.32 ± 0.04 Turkana Basin, Kenya, and Ethiopia

Ethiopian Rift Valley

Northern Tanzania

Figure 13.9 Stratigraphic Beds in the Turkana Basin, the Ethiopian Rift Valley, and Northern Tanzania Dated units are shown in each stratigraphic column. The colored line on the left edge of each column indicates an interval in which hominin fossils have been found. (Fossils have been lumped into 0.1-million-year intervals.)

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Figure 13.10 Paranthropus boisei OH 5, from Olduvai Gorge, Tanzania.

The Fossils of the Lake Turkana Basin

The African Rift Valley runs southward from the Ethiopian highlands into northern Kenya and the Lake Turkana basin. The Omo River, which drains the Ethiopian highlands, forms a large river delta where it enters Lake Turkana. The lake is 250 kilometers (155) miles long with a maximum width of 56 kilometers (35 miles).

On the eastern shore is the Koobi Fora region, an area of sediments that covers approx-imately 1000 square kilometers (386 square miles) and extends some 25 kilometers (15½ miles) inland from the shore of the lake. The Koobi Fora Formation is some 560 meters (1837 feet) thick and is divided into members by a series of tuffs. The fossils all occur between the Tulu Bor tuff dated at 3.3 million B.P. and the Chari tuff dated at 1.4 million B.P. (Figure 13.9). The Lake Turkana basin has revealed an excellent fossil record of pollen, freshwater shellfi sh, and many mammalian groups, including prehistoric members of the pig, cattle, horse, and elephant families.

Over 200 hominin fossils have been recovered from the both sides of the lake since work started in 1968. The fossils represent seven species. Here we will look at those species that are not part of the genus Homo: Paranthropus boisei, Paranthropus aethiopicus, Australopithecus anamensis, and Kenyanthropus platyops.

Paranthropus boisei and Paranthropus aethiopicus Several well-preserved specimens of Paranthropus boisei have been recovered from Koobi Fora. KNM-ER 406, shown in Figure 13.11, is of special interest since it was found in the same deposits as a fossil assigned to the genus Homo (Figure 14.3).

In 1984, excavations began west of Lake Turkana, where the Nachukui Formation extends 5 to 10 kilometers (3 to 6 miles) inland along the western shore of the lake. Inves-tigators found a cranium, KNM-WT 17000, at the site of Lomekwi (Figure 13.12). The fi nd was named the “Black Skull” because of its black color; the color was derived from the manganese-rich sediments in which it was found. WT 17000 appears to resemble P. boisei, yet this particular specimen is characterized by a small cranium and retention of some ancestral features from the earlier Australopithecus. The skull is dated at 2.5 million B.P.,

tuff Geological formation composed of compressed volcanic ash.

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Figure 13.11 Paranthropus boisei Side, front, and top views of KNM-ER 406 from East Lake Turkana, Kenya.

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somewhat earlier than the age range for P. boisei. Some paleoanthropologists place this fi nd in its own species, Paranthropus aethiopicus.

Australopithecus anamensis In 1995, Meave G. Leakey, Richard Leakey’s wife, and her colleagues published the description of a new species of Australopithecus. It was named Australopithecus anamensis. The name anamensis comes from anam, which means “lake” in the language of the Turkana people. The fossils were found at the site of Kanapoi, southwest of Lake Turkana. Additional material also has been found 48 kilometers (30 miles) away at Allia Bay on the eastern side of the lake. The sediments at both sites were once a part of an ancient lake of which Lake Turkana is a remnant. The habitat may have been one characterized by dry open woods or brush with gallery forest along the rivers. In 2006, additional Au. anamensis material, including the earliest australopithecine femur, was found in the Middle Awash of northeast Ethiopia. This discovery occurred only about 10 kilometers (6 miles) from the approximately 200,000 year earlier Ardipithecus ramidus fi nd as well as more recent australopithecine specimens.

The fossil beds at Kanapoi have been known for some time; a humerus was recovered at Kanapoi in 1965. The new material, discovered beginning in 1994, includes an incom-plete mandible with all its teeth intact, a partial left temporal, additional jaw fragments and isolated teeth, sections of a humerus, and sections of a tibia (Figure 13.13). The Kanapoi beds also include fossil fi sh, aquatic reptiles, and many terrestrial mammals.

The Kanapoi fossils have been dated by 40Ar/39Ar dating and by correlation with dated sediments at other east African sites. The fossils found in the lower horizon date

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Figure 13.12 Paranthropus aethiopicus KNM-WT 17000, the “Black Skull,” from Lomekwi, West Lake Turkana, Kenya.

Figure 13.13 Australopithecus anamensis From the site of Kanapoi, Kenya, left to right: Section of a right tibia that articulates with the foot; part of the knee of a right tibia; a mandible; and a maxilla.

between 4.17 and 4.07 million years ago. The upper horizon, which contains the post-cranial material, is not as precisely dated, but it is thought to date from between 4.1 and 3.5 million B.P. The Allia Bay fossils have been dated at 3.9 million B.P.

The tibia of Au. anamensis clearly belongs to an erect biped. The way in which muscles function in erect bipedalism produces stresses on bones that lead to a thickening of the bone. The presence of these thick regions on the tibia plus the structure of the end of the tibia where it articulates with the femur provides clear evidence of bipedal locomotion. Analysis of the fossils attributed to Au. anamensis have led some paleoanthropologists to suggest that Au. anamensis could be a direct ancestor to Au. afarensis.

Kenyanthropus platyops In 1999, paleoanthropologists, including Meave Leakey, were work-ing at Lomekwi on the western shore of Lake Turkana, where hominin material had been

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found earlier. The sediments are dated between 3.5 and 3.2 million B.P. Several new fossils representing parts of skulls were discovered, including a reasonably complete but distorted cranium. The cranium, WT 40000, is dated at 3.5 million years old (Figure 13.14).

WT 40000 was contemporary with Australopithecus afarensis, known from Hadar and Laetoli. Although WT 40000 shares many characteristics with Au. afarensis, it also exhibits some features found in the chimpanzee but not in Au. afarensis, such as a small ear opening. WT 40000 also has a number of unique features, such as a fl at plane beneath the nose bone, giving the appearance of a fl at face. In fact, it is the fl at face that is the most distinctive feature of the cranium, and this feature gives rise to its name Kenyanthropus platyops, “fl at-faced man of Kenya.” Because the fossil is distorted, not all paleoanthropologists believe that its described features represent the features of the specimen when it was alive. Some research-ers see it as more likely to be a specimen of Au. afarensis or a new australopithecine species. If it is a species other than Au. afarensis, then the presence of two distinct species liv-ing side by side means that they were probably not competliv-ing with each other. The differ-ences in facial morphology suggest that they were specialized for different diets and that they exploited different habitats. Analysis of the fossil remains of other animals and plants suggests that the habitat was fairly wet and vegetated, probably woodland. The habitat at Lomekwi was wetter and more forested than that at Hadar.

The Fossils of the Afar

The Afar is a low-lying depression spreading over northeastern Ethiopia and adjacent coun-tries. It is located at the junction of three tectonic rifts, a part of the Great Rift Valley of East Africa. Within the depression is the lowest point in Africa, 155 meters (509 feet) below sea level. It is a region of earthquakes, volcanic activity, and extreme heat. Running through the Afar is the Awash River, fl owing into a series of saline lakes.

In the past the area contained many freshwater lakes surrounded by open forests. Today, the lake beds and lake margins are represented by deep layers of sedimentary rocks. Living

Figure 13.14Kenyanthropus platyops KNM-WT 40000 from Lomekwi, Lake Turkana, Kenya, dated at 3.5 million B.P.

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Figure 13.15 Australopithecus afarensis Reconstructed skull from East Africa.

around these lakes and in the forests were many hominins whose remains became incorpo-rated into the sediments that make up the geology of the Afar.

Australopithecus afarensis In 1973, the International Afar Research Expedition, led by Yves Coppens, Maurice Taieb, and Donald Johanson, began working in the Afar at a site known as Hadar. Because of the special conditions of burial and fossilization, some fos-sils are very well preserved. Between 1973 and 1977, more than 240 hominin fosfos-sils were recovered. The stratigraphic beds date from between 3.6 and 2.9 million B.P. The fi rst hominin fi nd, consisting of four leg bones, was made in the fall of 1973. A partial femur and tibia fi t together to form a knee joint; this provided skeletal evidence of fully developed erect bipedalism. In 1975, the team discovered a collection of 197 bones representing at least 13 individuals, both adults and immatures. Some believe that these individuals, called the “First Family,” all died at the same time; they possibly were killed and buried by a sudden fl ood or another catastrophe. This material has been placed into the species Australopithecus afarensis (Figure 13.15).

Perhaps the best-known fossil is “Lucy” (AL 288-1), which was found in 1974 (Figure 13.16). This remarkable fi nd consists of 40 percent of a skeleton. “Lucy” provided the fi rst opportunity for anyone to study the skull and postcranial remains from the same individual of this antiquity.

After a break in time, paleoanthropologists returned to Hadar in 1990. Since then they have recovered 53 new specimens that are attributed to Au. afarensis. Among these is a cranial fragment dated at 3.9 million B.P., which makes it the oldest known specimen of this species.

In 1994, the team announced the discovery of three-quarters of a skull that was pieced together from more than 200 fragments. This specimen (AL 444-2) is dated at approximately 3.0 million B.P., which is about 200,000 years younger than “Lucy.” The skull is larger than that of “Lucy”; in fact, it is the largest known cranium outside the genus Homo. Many paleoanthropologists believe that it probably represents a male.

In 2000 a relatively complete skeleton was found at the site of Dikika, located not far from Hadar. The fossil, DIK-1/1, is that of a child, thought to be a three-year-old female. It was given the name Selam (“Peace”); it is also referred to as “Lucy’s Baby.” It is dated at

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3.3 million years ago, somewhat earlier than the Lucy skeleton from Hadar. Analysis of this fossil will provide valuable information about the early development of Au. afarensis individuals.

Finally, the site of Burtele has yielded several hominin fossils, includ-ing a well-preserved, partial foot skeleton, dated to about 3.4 million years ago. The foot lacks an arch and has a grasping big toe. It is possible that these fossils belong to a new australopithecine species that was contem-porary with Au. afarensis.

Australopithecus garhi In 1996 through 1998, a series of fossils were recovered from the Bouri Formation from the Middle Awash of Ethiopia. One of those fi nds was an incomplete cranium (BOU-VP-12/130), which has been dated to 2.5 million B.P. (Figure 13.17). Characterized by large anterior dentition and other distinctive details of dental anatomy, the cranial remains were placed in a newly created species, Australopithecus garhi. (The word garhi means “surprise” in the language of the Afar people.) The postcranial fossils are not associated with the cranial remains and therefore cannot be placed with certainty within the new species at this time. Associated bones of other animals show clear evi-dence of butchering activity in association with isolated stone tools.

The Laetoli Footprints

Laetoli is located in Tanzania, near Lake Eyasi; it is approximately 50 kilometers (31 miles) south of Olduvai Gorge. Mary Leakey and Tim White excavated the remains of several hominins dated between 3.8 and 3.6 million B.P. These fossils have been placed into the species Au. afarensis.

One day at Laetoli about 3.6 million years ago, a light fall of vol-canic ash fell over the land, and a light drizzle moistened the ash; later, hominins walked across the ash fi eld. A day or so later, another ashfall covered their tracks; the remaining impressions were dis cov ered in 1978. The site consists of two footprint trails more than 27.5 meters (90 feet) long. Thirty-eight footprints of a small hominin make up the western trail, and 31 footprints make up the eastern trail.

The eastern trail is not as well defi ned as the western trail. Some see the western trail as having been made by a female and the eastern trail as having been made by a large male. The trails are so close together that Ian Tattersall sees the hominins as “walking in step and accommodating each other’s stride.”3 The eastern trail is not as distinct as the western one because, as some paleoanthropologists believe, a third hominin was stepping in the large male’s footprints as the three hominins walked over the sticky ash fl ow. The footprints exhibit some specializations of the modern human foot that point to bipedal loco-motion on the ground. However, the individuals who made the prints had smaller feet than modern humans, and the bottom of the foot displayed a less developed arch and a big toe whose divergence from the other toes is intermediate between that of modern humans and that of modern great apes (Figure 13.18).

The Fossils of Chad

The distribution of known specimens of Australopithecus and Paranthropus has led many paleontologists to conclude that these early hominins existed only in the eastern and Figure 13.16 Australopithecus afarensis

“Lucy” (AL 288-1), a female Au. afarensis skeleton from Hadar, Ethiopia.

See the Online Learning Center for an Internet Activity on

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Figure 13.17 Australopithecus garhi BOU-VP-12/130 from the Middle Awash, Ethiopia.

Figure 13.18 Hominin Footprints at Laetoli, Tanzania

southern regions of the African continent. Yet this apparent distribution of early hominin populations may simply be a refl ection of the distribution of known fossil sites from this time. The announcement in 1995 that a fossil had been recovered in northern Chad, some 2500 kilometers (1550 miles) west of the Rift Valley, suggests that the distribution of the early hominins may be greater than that suggested by the better-known South and east African sites.

In 1993, several sites were discovered in the region of Bahr el Ghazal near Koro Toro in northern Chad. A fragment of an adult hominin mandible, which contains the crowns of several teeth, was recovered from the site known as KT 12; the fossil is known as

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KT12/H1 (Figure 13.19). The fi nd is associated with other animal fossils that have been dated between 3.5 and 3.0 million years B.P.

The Chad mandible resembles Au. afarensis in many ways yet differs from other specimens of that species in some fea-tures. In 1996, the discoverers placed the specimen into the new species Australopithecus bahrelghazalia.

Drawing a Family Tree

Paleoanthropologists see a signifi cant amount of diversity among the early hominins. The question arises: Does this vari-able assembly of specimens represent a few highly varivari-able spe-cies or does it represent a larger number of different spespe-cies? Figure 13.19Australopithecus bahrelghazalia

Fragment of an adult mandible (KT12/H1) from northern Chad.

5 5.5 4.5 3.5 2.5 2 1.5 0.5 0 1 3 4 4.5 3.5 2.5 2 1.5 0.5 0 1 3 4 Millions of years H. heidelbergensis H. sapiens H. neanderthalensis H. erectus H. ergaster H. habilis H. rudolfensis Homo sp. Au. afarensis Australopithecus anamensis Ardipithecus ramidus Au. africanus P. robustus P. aethiopicus P. boisei (a) Later homo H. erectus P. robustus Kenyanthropus platyops Au. bahrelghazali Ardipithecus ramidus Au. anamensis K. rudolfensis Au. garhi Au. afarensis

P. aethiopicus Au. africanus P. boisei Au. (H) habilis H. ergaster (b) ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

Figure 13.20 Phylogenetic Trees Showing Possible Relationships among Fossil Hominin Species (a) Published in 1994 and (b) published in 2001. (a) B. Wood, “The Oldest Hominid Yet,” Nature 371 (1994), p. 280. (b) D. E. Lieberman, “Another Face in Our Family Tree,”

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Some paleoanthropologists argue that the range of variation among the early hominins may have been greater than that found among contemporary apes. For example, the degree of sexual dimorphism may have been considerably greater than that found among living humans and apes.

The specimens from Hadar and Laetoli provide a good example of this dilemma. Many paleoanthropologists see these fossils as representing a single species, Au. afarensis. The smaller specimens, such as “Lucy,” would represent females, while the larger, more robust material, represented by AL 444-2, would represent males. If there is only one species present at this time, then Au. afarensis could be the common stock from which the later Australopithecus, Paranthropus, and Homo evolved.

Other paleoanthropologists see the Hadar and Laetoli populations as presenting two different species. One population shows robust features that would later lead to Paranthropus; the other population includes “Lucy” and leads to Au. africanus and Homo.

The picture is further complicated by the recent discoveries of many new fossils. These differ suffi ciently from one another and from known specimens that several new species and genera have been proposed. All or some of these may not be valid.

As each new fi nd is published, a new interpretation of the fossil record is proposed. We, however, must see each new scheme as tentative, for a new discovery in the not-too-distant future could bring about yet another proposal. Perhaps it is best to remember what was said in Chapter 11 and think about each fossil as a piece of a large, complex puzzle. As more and more fossils are discovered, and as newer methods of analysis are developed, the puzzle will become clearer.

For these reasons we are reluctant to show the relationship among the known fossils as a certain reconstruction of our evolutionary history. However, to illustrate the complexity of this task, we present in Figure 13.20 two evolutionary trees, one published in 1994 and the other in 2001. Of course, the earlier one contains fewer species since many were not yet proposed at the time it was developed.

Summary

The fossil evidence of hominins that fall outside of the genus Homo are found on the African continent: South Africa; the east African countries of Ethiopia, Kenya, and Tanzania; and the north central African country of Chad. Figure 13.1 is a map of many of the African sites that have yielded the material discussed in this section. No evidence has been found to suggest that Australo pithecus or Paranthropus existed outside the African continent. It appears that Charles Darwin was correct when he stated that human ancestors originated in Africa. The fi rst of the fossils to be discovered was at Taung, South Africa, in 1924. Raymond Dart placed the juvenile skull in the species Australopithecus africanus. Today we have many fossils from several South African caves that are placed into two species: Au. africanus and P. robustus.

Early hominins are well known from several east African sites associated with extensive sedimentary deposits. Prehistoric volcanic activity associated with these beds provides material for chronometric dating. The most signifi cant sites are those of Olduvai Gorge, Koobi Fora, West Lake Turkana, Kanapoi, Hadar, Dikika, the Middle Awash, and Laetoli. The fossils have been assigned to several species. They are listed in Table 13.1.

Table 13.2 lists the sites that we have discussed. The table also lists for each site the hominin species found; however, there are many controversies surrounding the placement of particular fossils in particular species. The dates for many hominin sites are also tentative.

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Table 13.2 Summary of Major Early Hominin Sites

Estimated Age

Site (million years B.P.) Species Present

South Africa

Taung 2.6–2.4 Australopithecus africanus

Sterkfontein and

Jacovec Caverns 4.0–2.5 Australopithecus africanus

Swartkrans 1.7–1.1 Paranthropus robustus

Kromdraai ? Paranthropus robustus

Makapansgat 3.0–2.6 Australopithecus africanus

Gladysvale ? Australopithecus africanus

Drimolen 2.0–1.5 Paranthropus robustus

Malapa 2.0 Australopithecus sediba

Tanzania

Olduvai Gorge 1.75 Paranthropus boisei

Laetoli 3.7–3.5 Australopithecus afarensis

Peninj 1.3 Paranthropus boisei

Kenya

Koobi Fora 3.3–1.4 Paranthropus boisei

Lomekwi 2.5 Paranthropus aethiopicus

3.5 Kenyanthropus platyops

Lothagam 5.5–5.0 ?

Kanapoi 4.2–4.1 Australopithecus anamensis

Allia Bay 3.9 Australopithecus anamensis

Tabarin 4.2 Australopithecus afarensis

Ethiopia

Omo 3.3–2.1 Australopithecus afarensis Paranthropus aethiopicus Paranthropus boisei

Hadar 3.6–2.9 Australopithecus afarensis

Maka 3.4 Australopithecus afarensis

Burtele 3.4 ?

Dikika 3.3 Australopithecus afarensis

Bouri 2.5 Australopithecus garhi

Konso 1.4 Paranthropus boisei

Chad

KT 12 3.5–3.0 Australopithecus bahrelghazalia

Table 13.1 Summary of Early Hominin Species

Species Time Period (million years B.P.) Distribution

Australopithecus anamensis 4.2–3.9 East Africa

Australopithecus afarensis 3.9–3.0 East Africa

Kenyanthropus platyops 3.5 East Africa

Australopithecus bahrelghazalia 3.5–3.0 North Central Africa

Australopithecus africanus 3.5–2.5 South Africa

Australopithecus garhi 2.5 East Africa

Paranthropus aethiopicus 2.5 East Africa

Paranthropus boisei 2.3–1.4 East Africa

Australopithecus sediba 2.0 South Africa

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EARLY HOMININS: INTERPRETATIONS OF THE EVIDENCE

The genera Australopithecus and Paranthropus together form a group of hominins, often referred to as the australopithecines, that contrast with the hominins belonging to the genus Homo. Australopithecus existed earlier in time than Homo; however, Paranthropus was con-temporary with early members of the genus Homo. Most likely a species of Australopithecus gave rise to Homo.

Australopithecus and Paranthropus are characterized by a small cranial capacity, a relatively large projecting facial skeleton, large premolars, molars with thick enamel, and postcranial features that suggest that their primary means of locomotion was erect bipedalism. Other than these general features, these genera are quite variable. The vast length of time during which these genera existed, their considerable geographical variation, and the frag-mentary nature of much of the fossil material make it diffi cult to make broad generaliza-tions. What follows are descriptions and interpretations of the evidence. The ideas presented here are hypotheses that will be modifi ed as new evidence is uncovered and as new ways of interpreting the evidence are developed.

The major landmarks of hominin evolution are the evolution of habitual erect bipedalism, reduction in the size of the dentition, the development of tool use and tool manufacture, and enlargement of the brain. Generally, it is assumed that these landmarks evolved in the order listed. We will discuss the evidence in the same order.

Australopithecines as Erect Bipeds

The anatomical evidence for erect bipedalism is found in the postcranial skeleton. Also, as Raymond Dart observed, the forward position of the foramen magnum in the base of the skull also can be used to infer upright posture. A modest number of early hominin postcranial bones are known.

The size of the early hominins can be estimated from the dimensions of the postcranial bones. They were relatively small compared with modern humans and the great apes. The average reconstructed weight for the four best-known species (Au. afarensis, Au. africanus, P. robustus, and P. boisei) ranges from 40 to 49 kilograms (88 to 108 pounds) for males and from 29 to 34 kilograms (64 to 75 pounds) for females (Table 13.3). The average reconstructed stature ranges from 132 to 151 centimeters (52 to 59 inches) for males and from 105 to 124 centimeters (41 to 49 inches) for females. The degree of sexual dimorphism is greater than that found in the genus Homo.

Fossil Evidence for Erect Bipedalism The postcranial skeletons of Australopithecus and Paranthropus are those of erect bipeds. The pelvis, which is bowl-shaped and shortened from top to bottom, is similar in basic structure to that of H. sapiens (Figure 13.21); the spine shows a lumbar curve. Erect bipedalism also is deduced from analysis of the footprints discovered at the site of Laetoli in Tanzania.

Table 13.3 Estimated Sizes of Hominin Paleospecies

Body Weight (kilograms) Stature (centimeters) Female as Female as Paleospecies Male Female % of Male Male Female % of Male

Au. afarensis 45 29 64 151 105 70

Au. africanus 41 30 73 138 115 83

P. robustus 40 32 80 132 110 83

P. boisei 49 34 69 137 124 91

H. sapiens 65 54 83 175 161 92

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(a) (b) (c)

Figure 13.21 Early Hominin Pelvis The pelvis of (b) Australopithecus africanus compared with the pelvis of (a) a modern chimpanzee and (c) a modern human.

There is other evidence for erect bipedalism. Four bones of a left foot belonging to Au. africanus (Stw 573) fi t together to form an arch that extends from the heel of the foot to the beginning of the big toe. The bones show a mixture of humanlike as well as apelike features; the apelike features are more evident in the bones closer to the toe. The

investiga-tors concluded that the foot with its grasping big toe was adapted for arboreal climbing as well as for bipedal loco-motion.

The postcranial skeleton of Au. afarensis is of special interest because it exhibits several features that illustrate its transitional status (Figure 13.22). The skeleton exhibits a number of specializations for erect bipedalism. The blade of the ilium is short and broad, the foot possesses a human-like arch, and the big toe is nongrasping. However, the near-contemporary foot skeleton from Burtele lacks an arch and possesses a grasping big toe.

Hominins maintain their center of gravity over their legs when standing and walking. This is made possible, in part, by the femur angling in toward the knee, as seen in Figure 8.6. When standing, the knees are positioned close together. In part of the walking cycle, the weight of the body is cen-tered over one leg while the other leg is moving. This balance on one leg is possible because the center of gravity of the body remains over the one knee while the opposite leg is raised off the ground. The short legs of Au. afarensis suggest that it had a signifi cantly shorter stride than modern humans; this means that its speed on the ground was likely to have been slower than that seen in humans today.

Other features of the postcranial skeleton suggest that Au. afarensis engaged in some arboreal locomotion in addi-tion to erect bipedalism. The curved, slender fi ngers and the curved toes are intermediate in relative length between those of apes and those of humans. These features show a degree of grasping that could have functioned as part of an arboreal locomotor pattern. The ability to sleep in trees and to use trees for protection from predators may have been an important factor in the survival of early hominin popula-tions. In addition, these populations may have exploited arboreal food resources.

Figure 13.22 Reconstruction of “Lucy” The drawing on the right represents a reconstruction of AL 288-1 from Hadar. The original fossils are shown in black except in the skull. The remainder of the reconstruction is based on construction of mirror images of known parts of the skeleton and reconstructions based on other fossils. Note the long arms and curved fi ngers. A modern human skeleton is shown for comparison.

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Many paleoanthropologists have concluded that erect bipedalism is very ancient in the hominins and may have been the most signifi cant factor that distinguished hominins from ape ancestors around the time of the divergence of the two lineages. In Chapter 12 we looked at the partial skeleton of Ardipithecus ramidus from the Middle Awash of the Afar, dated at 4.4 million years old. The skeleton exhibits a mosaic of specializations for erect bipedalism and arboreal locomotion, although the upper limb lacks features for suspensory behavior.

Many hypotheses have been put forth over the years to explain why erect bipedalism evolved in the hominins. Erect bipedalism permits hominins to walk on the ground and reach up into the trees for food. It permits them to transport food, tools, and relatively helpless infants in their hands while moving from one place to another. The emancipation of the hands from locomotor functions permits the evolution of the hands into highly developed organs of manipulation that are better for the manufacture of tools. Erect bipeds can walk a greater distance using less energy than quadrupeds can and, with their eyes elevated above the ground, can see over grasses and see a longer way into the distance; this is critical for an animal that emphasizes vision. The air is slightly cooler off the ground, and erect bipedalism exposes less surface area of the body to the hot midday sun. It also may have something to do with phallic display. Perhaps each of these hypotheses contains an element of truth, since erect bipedalism allows for a complete integration of several functions.

Early Hominin Tool Use

Raymond Dart noted the presence of many broken bones in the deposits at Makapansgat. He concluded that they were a result of the deliberate manufacture of bone tools. He termed this an osteodontokeratic culture, from osteo, meaning “bone”; donto, meaning “tooth”; and keratic, meaning “horn” (keratin is a main constituent of horn). He saw a femur as a club, a broken long bone as a sharp cutting tool, and a piece of mandible as a tooth scraper. However, later studies by C. K. Brain of the bone material from Swartkrans demonstrated that the features of the bones that suggest deliberate toolmaking to Dart were more likely the result of carnivore activity.

In spite of the diffi culties in interpreting the bone material in South Africa, paleoan-thropologists still believe that tool use and tool manufacture are an important element of early hominin behavior (Box 13-2). The report that modern chimpanzees manufacture tools suggests that such behavior could have characterized the early hominins. Although the earliest hominins may have used their hands for some degree of arboreal locomotion, the fact that they were erect bipeds means that they would have had their hands freed from primary locomotor functions. These facts lead us to expect an early expression of culture in these prehistoric populations.

The earliest hominin tools most likely were made of perishable materials such as wood, bark, leaves, and fi bers. However, the evidence for tool use in the archaeological record consists primarily of stone objects. Early stone tools were probably nothing more than fortuitously shaped natural objects. An example is a small, rounded stone that would fi t comfortably in the hand and could be used to crack open a nut to obtain the meat or to break open a bone to obtain the marrow. Such unaltered stones were probably used as tools by early hominins for a long period of time before stones were deliberately altered to achieve a specifi c shape. It is very diffi cult to interpret stones found in a site in association with hominin fossils, since such stones may have been unaltered stones used as tools or simply stones deposited in a site through geological activity.

The fi rst concrete evidence of the manufacture of stone tools comes from a site near the Gona River in Ethiopia; this site is dated at 2.6 million B.P. (Figure 14.22). Another early location is the Shungura Formation at Omo, which is dated between 2.5 and 2.4 million B.P. Stone tools also are known from many sites dated between 2.5 and 1 million B.P. However, all these examples of early stone tools are probably associated with early mem-bers of the genus Homo.

osteodontokeratic

culture An archaeological

culture based on tools made of bone, teeth, and horn.

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Box 13-2

Anthropologist Joseph S. Eisenlauer notes that the term tool as it appears in the anthropological literature frequently is applied to such a broad range of objects that the true signifi cance of this functionally distinct category of implements is largely obscure. He suggests a more focused defi nition. Specifi cally, he regards as “tools” only those implements that are used to make, maintain, repair, and/or modify other objects or to process raw materials. The termite stick of the chimpanzee would not be a tool under this defi nition, whereas a hammerstone used in making a fl int projectile point would be.

Another anthropologist, Wendell Oswalt, suggests the name subsistant for implements such as the termite stick. The difference between the termite stick and the hammer is more signifi cant than it fi rst might appear. The termite stick is simply an imple-ment used in helping to secure food. The hammerstone is used to manufacture something else.

Eisenlauer believes that the mental step from simply using or even making with one’s hands or teeth an object to help get food to using one object to manufacture another was one of the most signifi cant steps in the evolution toward modern hominins. The use of a hammerstone presupposes mental processes by its user that are not necessary to the user of the termite stick. The reason one makes a hammerstone is to use it to modify some-thing else, the fi nished form of which is only an idea in the

maker’s head. The termite stick is simply used to secure termites as food.

In the case of humans and chimpanzees, anatomy affords a limited range of technological capabilities. For instance, neither species can effectively carve wood with its teeth. Conceiving of the idea that one implement could be used to produce others is a hallmark of human evolution. This step was never taken in the evolutionary line leading to chimpanzees.

Although we continue to use the word tool in its general sense, Eisenlauer’s point is well taken. There was an evolution in the use of implements. Perhaps the earliest stage was simply to use an unmodifi ed object for some reason, for example, throw-ing a rock at another individual. Then implements may have been modifi ed specifi cally for food getting or other direct survival rea-sons. Next, objects would be fashioned to make other objects. In the process the human body would become a manipulator of tools rather than being a tool itself. This may have been the point where protocultural behavior at the technological level evolved into the unique technological cultural behavior of hominins.

Sources: J. S. Eisenlauer, Personal Communication, 1999; J. S. Eisenlauer,

Hunter-Gatherer Tools: A Cross-Cultural Ethnoarchaeological Analysis of Production Technology (Ann Arbor: UMI Dissertation Services, 1993); W. H. Oswalt, An Anthropological Analysis of Food-Getting Technology

(New York: Wiley, 1976).

312

Bones of mammals found at Bouri, which are associated with the remains of Au. garhi, exhibit evidence of cut marks made by stone tools as well as scars made by the impact of stone tools against the bone (Figure 13.23). The alterations of the bone provide evidence of several food extraction behaviors, including the disarticulation of body parts, removal of fl esh from the bones, and the breaking open of bones to extract the marrow.

Fossilized animal bones from Dikika, in the Afar of Ethiopia, were observed with a scanning electron microscope. Two types of marks were seen. Some of the marks were cut marks made by a stone tool with a sharp edge used to cut meat from the bone. The other marks were percussion marks made by hammerstones. They were used to crack open long bones presumably to get at the marrow within. The bones are older than 3.39 million years and were probably used by Au. afarensis. No actual stone tools were found.

The Early Hominin Hand Further evidence for early hominin toolmaking lies in the anat-omy of the hand. Randall Susman has compared the hand bones of Au. afarensis, P. robustus, H. erectus, and fossil H. sapiens with those of contemporary humans, chimpanzees, and bonobos.4 He observes that ape hands are characterized by long, curved fi ngers, narrow fi ngertips, and relatively small thumbs. The ape hand is most frequently used in a power grip, where an object is held against the palm of the hand by the fi ngers.

Humans, in contrast, have relatively short, straight fi ngers. The human thumb is relatively long; this results in a ratio of thumb to fi nger length that makes it possible to rotate the thumb so that the tip of the thumb can oppose the tip of each fi nger in turn. The thumbs and fi ngers possess broad fi ngertips. This thumb is well adapted for a precision grip.

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1 cm

Figure 13.23 Evidence of Tool Use This is a photograph of the midshaft of a right tibia of a large bovid (cattle-like animal) from the Middle Awash, Ethiopia. The arrows indicate the direction of the impact of a hammerstone. In the enlargement we can see large fl akes produced by the impact of a hammerstone and adjacent cut marks. The goal of this activity was probably to extract the marrow from the interior cavity of the bone.

There are no stone tools associated with fossil remains of Au. afarensis. The hand bones of this species show many apelike features, such as a short thumb with curved phalanges in the other fi ngers. In contrast to the hand skeleton of Au. afarensis, the hand of the later P. robustus is consistent with a precision grip. The precision grip is considered to be a requirement for complex toolmaking.

The humanlike anatomy of the P. robustus hand and the presence of stone tools at the site of Swartkrans suggest that the later Paranthropus made tools. Yet tools may have played very different roles in Homo and non-Homo populations. The importance of tool technology to human evolution is discussed in the next chapter.

Early Hominin Dentition

The majority of known early hominin fossils are isolated teeth and jaw fragments with teeth. In general, the dentition of Australopithecus and Paranthropus resembles that of Homo. Yet the early species of Australopithecus show many nonhominin features, while Paranthropus evolved rather specialized dentition.

The dental arcade of Au. afarensis is intermediate in shape between that of modern humans and that of apes (Figure 13.24a). The posterior teeth lie in a fairly straight line, except for the third molar, which is positioned inward. The upper incisors are relatively large and project forward. The canines project above the tooth row, and they are conical in

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shape, in contrast to the spatulate shape of the modern human canine. A small diastema frequently occurs between the upper canine and incisor.

The anterior lower premolar is of special interest. As we saw in Chapter 8, the ape premo-lar is sectorial; it consists of a single cusp that hones against the upper canine. This contrasts with the modern human bicuspid premolar. The anterior lower premolar in Au. afarensis appears to be transitional between those of apes and those of modern humans. It shows a slight develop-ment of the second cusp (Figure 13.25).

The apelike character of Au. afarensis is no longer seen in the more recent Au. africanus (Figure 13.24b). Although the teeth are relatively larger than those of later Homo, now the dentition is basically humanlike. However, the dentition of Paranthropus shows many spe-cialized features (Figure 13.24c). These include thickened tooth enamel and an expansion in the size of the surface area of the premolars and molars. These and other changes may be related to a specialized diet that consisted of tough, fi brous materials.

Deciduous Dentition The early hominin fossils include dentition from infants and juveniles, including the “Taung Baby.” This jaw contains a complete set of deciduous teeth and fi rst adult molars in the process of erupting. In modern humans, these features would characterize the dentition of a six-year-old child.

Because of the Taung fossil, many paleoanthropologists see evidence of a long child-hood period in Australopithecus. One feature of modern humans is a lengthened childchild-hood

(a) (b) (c)

Figure 13.24 Early Hominin Dentition Upper dentition of (a) Australopithecus afarensis (AL 200-1a), (b) Australopithecus africanus (Sts 52b), and (c) Paranthropus boisei (OH 5). Reprinted by permission of Waveland Press, Inc., from Clark Spensor Larsen, Robert M. Matter, and Daniel L. Gabo, Human Origins: The Fossil Record, 3rd ed. (Prospect Heights, IL: Waveland Press, 1998). All rights reserved.

Chimpanzee Au. afarensis

Human A A A B B

Figure 13.25 The Hominin Premolar The anterior lower premolar from Au. afarensis is compared with the premolars from a chimpanzee and a modern human. The human premolar is characterized by two cusps, A and B, while the chimpanzee sectorial premolar has only one cusp. Note that the premolar of Au. afarensis is intermediate with a small development of cusp B.

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period compared with that of apes. This prolonged maturation is related to the development of learned behavior as a major mode of hominin adaptation.

However, analyses of the dentition of Australopithecus, apes, and modern humans contradict the idea that the length of the early hominin childhood was more like the human pattern than the ape pattern. In one study, the development of the dental crowns and that of dental roots of several fossil specimens were plotted against the development standards of both modern humans and apes. The dental pattern of Australopithecus best fi ts the ape pattern. For example, in the apes the canine erupts after the eruption of the fi rst molars; this contrasts with the earlier eruption of the canine in contemporary humans. In Australopithecus, the eruption of the canine is delayed in the same way as it is in the apes. This fact suggests that these forms had a relatively short maturation period, which is similar to those of chimpanzees and gorillas today. On the other hand, the dental pattern of Paranthropus does not appear to closely resemble the dentition of either humans or apes.

New medical technology, in particular the computerized axial tomography (CAT) scan, has been used to visualize the juvenile skull from Taung. Investigators scanned the Taung skull and compared it with scans of both a human and a chimpanzee at the same stage of fi rst-molar eruption. The scans revealed that the Australopithecus dentition growth and eruption pattern more closely resembled that of a three- to four-year-old chimpanzee than that of a fi ve- to seven-year-old human. Studies of bone growth in the Taung facial skeleton show a pattern similar to that of the chimpanzee. All these studies suggest that the prolongation of childhood may be a relatively late development in hom-inin evolution.

The Early Hominin Brain

An important part of hominin evolution is the story of the development of the brain. Brains are not normally preserved in the fossil record. However, brain size and some very general features of brain anatomy are refl ected in the size and structure of the cranium, or brain case.

The size of the brain can be estimated by measuring the volume, or cranial capacity, of the brain case (Chapter 8). The cranial capacities of specimens of Australopithecus and Paranthropus vary from 400 to 530 cubic centimeters (Table 13.4). These cranial capacities refl ect a small brain compared with that of modern H. sapiens, which averages about 1350 cubic centimeters. In general, the smallest cranial capacities belong to Au. afarensis, while the largest are found in Paranthropus.

Table 13.4 Cranial Capacities of Early Hominin Paleospecies

Cranial Capacity Species Specimen Site (cubic centimeters)

Au. afarensis AL 333-45 Hadar 500

Au. afarensis AL 162-28 Hadar 400

Au. africanus Sts 5 Sterkfontein 485

Au. africanus Sts 60 Sterkfontein 428

Au. africanus MLD 37/38 Makapansgat 435

Au. garhi BOU-VP-12/130 Bouri 450

Au. sediba MH 1 Malapa 420

P. aethiopicus WT 17000 West Lake Turkana 410

P. robustus Skw 1585 Swartkrans 530

P. boisei OH 5 Olduvai Gorge 530

P. boisei KNM-ER 406 Koobi Fora 510

P. boisei KNM-ER 13750 Koobi Fora 475

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Some insights into the mentality of the early hominins might be revealed by an analysis of the structure of the brain. As we saw in Chapter 8, it is possible to make an endocranial cast that represents the shape and features of the inside of the brain case. Several natural endocranial casts also have survived. These casts provide some informa-tion about the pattern of convoluinforma-tions and the locainforma-tion of grooves on the surface of the brain. Although this line of research is controversial, the early hominin brain appears to exhibit a simpler pattern of convolutions with fewer grooves than are found in the mod-ern human brain. It is, however, very diffi cult to make behavioral interpretations of this evidence.

Erect Bipedalism and the Brain Although the evolution of a large brain is one of the most striking features of the hominins, brain size remained relatively small for a long period of time. Why did the increase in brain size occur late in hominin evolution?

In Chapter 8 we saw that in the evolution of the human pelvis a repositioning of the sacrum in hominins created a complete bony ring through which the birth canal passes. In the chimpanzee, the articulations of the sacrum to the innominate bones and the pelvis to the femur are farther apart than in humans, which mean that the birth canal has a bony roof at one point and a bony fl oor at another. In humans, the bony roof has moved over the bony fl oor, creating a complete bony ring through which the head of the child must pass at birth (Figure 13.26). The fl exibility of the human infant’s skull, however, allows for a certain degree of compression as the child passes through the birth canal, and for a great deal of growth after birth.

Other animals’ brains are almost completely developed at birth. For instance, the rhe-sus money at birth has a brain that is approximately 75 percent of its adult size, and the brain of a chimpanzee newborn is 45 to 50 percent of its adult size. In contrast, the human newborn has a brain less than 30 percent of its adult size, attaining over 90 percent of its adult size by the fi fth year of age. Because the human brain grows and matures more slowly

Inlet

Midplane

Outlet

Chimpanzee Human

Figure 13.26 Pelvis and Fetal Head This diagram shows a female pelvis of a chimpanzee and that of a human from below. Note the size of the head of the fetus in childbirth at the level of the pelvic inlet, midplane, and pelvic outlet.

anterior pillars Bony

columns located on both sides of the nasal aperture of some fossil hominins that help withstand the stresses of chewing.

pneumatized The pres ence

of air spaces within some bones of the skull.

temporal-nuchal crest A

crest on the back of the skull, forming on the occipi tal and temporal bones.

postorbital constriction

As seen from a top view, a marked constriction in the skull immediately behind the orbits and brow ridge.

References

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