Sahelanthropus tchadensis (TM ) cranium 6-7 MYA. The Sahelanthropus tchadensis cranium was discovered by Michael Brunet's team in Chad in

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1 Sahelanthropus tchadensis (TM ) cranium 6-7 MYA. The Sahelanthropus tchadensis cranium was discovered by Michael Brunet's team in Chad in 2001 and described in Nature in The specimen has been significantly distorted, and reconstructed through computer manipulation. Cranial capacity= cc. The plane of the foramen magnum in relation to the orbits (indicating the position of the head during normal locomotion) suggests it may indicate bipedalism. However no postcrania are assigned to this species (other fossils include: 4 partial mandibles and 4 isolated teeth). Differences from chimpanzees include less projecting (prognathic) maxilla (upper jaw), relatively small canines, lack of canine/premolar honing complex, and a thick and continuous browridge. Tooth enamel thickness is intermediate between chimpanzees (thin) and australopithecines (thick). The lack of prognathism is a challenge to asserting that S. tchadensis is ancestral to australopithecines from ~4-2.5 mya, who exhibit much greater prognathism (more chimp-like ) than S. tchadensis. Some suggest that S. tchadensis existed near the time that hominids and apes separated on their evolutionary paths. It could be that this specimen is a representative of an early hominid, predating A. afarensis by 3 to 4 million years. On the other hand, it might be an ancestor of the gorilla. The characteristics of the cranium are a mosaic of hominin-like (short face, the size and shape of the canines), and ape-like (very large browridges and small brain case) features.

2 Kenyapitecus platyops KNM-WT 4000 cranium 3.5 MYA. The Kenyanthropus platyops (meaning "flat faced hominid from Kenya") cranium KNM-WT was discovered in 1999 by J. Erus, a member of Meave Leakey's team, west of Lake Turkana, Kenya. In 2001 Leakey, et al. described the specimen in Nature. Some additional cranial fragments, partial jaws, and isolated teeth may be from K. platyops, but there are no postcrania. The cranium is relatively complete and well preserved, but quite distorted. The date indicates that this specimen is contemporary with A. afarensis, indicating the presence of multiple hominin species at this time. The endocranial capacity cannot be precisely determined, but is within the range for A. africanus, ~ cc. The cheek teeth are smaller than A. anamensis and A. afarensis, although there is quite a bit of variability in the size of molars in both those australopithecines. The tooth enamel is quite thick, as in the robust autralopithecines. Some aspects of the cranium are similar to chimpanzees, Ardipithecus ramidus, and A, anamensis. However, K. platyops is similar to other australopithecines in the forward insertion of the cheekbones (zygomatic arches) on the maxilla (upper jaw), large face size in comparison with the braincase, and indications of molarization of the premolars. It is distinct from australopithecines in exhibiting only moderate prognathism (projection of the subnasal region), marked flatness of the face adjacent to the nasal opening, and a tall, vertically oriented cheek region the distortion makes some inferences problematic. Some of these facial characteristics are similar to KNM-ER 1470, and early Homo rudolfensis specimen. The classification of this specimen as a separate genus is not uncontroversial, especially given the damaged condition (1,100 face pieces) in which the cranium was found. Some researchers emphasize that the specimen was so deformed that it is difficult to interpret its position in hominin evolution.

3 Paranthropus aethiopicus KNM-WT cranium (the Black Skull ) 2.5 MYA. The Paranthropus aethiopicus cranium KNM-WT was discovered by A. Walker in 1985 on the west shore of Lake Turkana in northern Kenya. It was described by Walker, Leakey, Harris and Brown in Nature in The cranium is commonly referred to as the "Black Skull" due to its blueblack color, which is due to staining from manganese in the sediments where it was buried. Some partial mandibles and isolated teeth have been assigned to this species. Although not considered on a direct line to humans, it gives insights into early hominid evolution. P. aethiopicus shares many primitive features with A. afarensis, such as a relatively flat (unflexed) cranial base, extensive pneumatization of the base (filled with sinuses, air cavities), strong forward projection of the face below the nose (alveolar prognathism), and a very small cranial capacity (410 cc). It also has features typical of robust australopithecine species, For example, P. aethiopicus has a dish shaped midface region, forward position of the cheek bones (zygomatic arches), very large molars and especially the premolars, linear arrangement of the incisors and canines. The age of the cranium suggests it could be ancestral to both other recognized forms of robust australopithecines, P. boisei and P. robustus.

4 Australopithecus afarensis (AL 288-1) Lucy mandible 3.2 MYA Australopithecus afarensis, "Lucy" A.L , jaw KO-036-J. Discovered by Donald Johanson in 1974 in Ethiopia. A. afarensis is known from specimens of over 400 individual fossils representing all portions of the skeleton. Multiple jaws are the primary source of data on morphological variation in A. afrensis, and some postcrania are available. The Lucy specimen (AL 288-1) is a 40% complete adult skeleton. This mandible, associated with the partial cranium of Lucy, shows a narrow mandibular body showing the U-shaped morphology in contrast with the wider and more rounded mandible of later Homo and modern humans. The buccal (lateral or outer) walls of the mandible show a slight hollowing. The anterior (front) and lingual (interior) portion of the mandible is heavily reinforced, which is similar to the morphology of chimpanzee mandibles. The endocranial capacity of A. afarensis has a mean of 434 cc. Size differences among some specimens suggests to some researchers that A. afarensis may exhibit sexual dimorphism.

5 Australopithecus afarensis (AL 288-1) Lucy pelvis The reconstructed the "Lucy" pelvis by using casts of the left innominate and sacrum, which were part of the discovery and creating a mirror match for the right innominate (colored gray in the illustration). The shape of the pelvis clearly indicates that "Lucy" walked upright. The pelvis is slightly wider than in modern humans, possibly due to a more apelike trunk structure. The wider pelvis than seen in apes angles the femur (thighbone) to the knee, keeping the center of mass over the leg. Other differences may be due to the much later hominin evolution of the obstetric pelvis that allowed the passage of large brained infants. The morphology of the pelvis and femur unquestionably indicate that A. afarensis is a committed biped for it terrestrial locomotion. The distal (lower) condyle (articular end) of the femur shows a more oval or flattened x-section, which is similar to modern humans and unlike the rounded condyles of chimpanzees. This is part of morphologies that show A. afarensis possessed a knee that functions in the way modern humans do to center the trunk over the leg. This valgus knee is a behavioral response to habitual bipedal walking. Modern human infants do not show this morphology until their bones respond to habitual activity as they begin to walk regularly. The longer arms, shoulder morphology, and hands suggest either climbing capabilities in combination with terrestrial bipedality, or retention of past adaptations to arboreal locomotion. A. afarensis has a proportionally shorter femur (thighbone) compared with more recent hominins and modern humans, and the is more apelike. This and other morphology of the trunk, neck, and upper limbs all suggest that A. afarenis had more apelike body proportions than later hominins.

6 Australopithecus africanus Taung facial skeleton and mandible(plaster) 2.3 MYA. The Australopithecus africanus Skull (Taung Child) was discovered by M. de Bruyn in Taung, South Africa in Anatomy professor Raymond Dart identified this juvenile skull as a new genus and species of hominid in 1925 in Nature (Australopithecus africanus, meaning "southern ape of Africa"). In addition to the cast of the bones you see, there was an endocranial cast, a dissolved limestone impression of the interior of the braincase (apparently destroyed during excavation). Dart considered his new man-like ape to be intermediate between humans and apes. The skull, though immature, features several hominid-like characteristics including: a rounded, high forehead lacking browridges, rounded dental arcade, no space between canine and first lower premolar, and a foramen magnum (the hole under the skull from which the spinal cord emerges) positioned forwardly under the skull, indicating bipedal locomotion. On the other hand, the child's cranial capacity is estimated at 405 cc, with a projected adult size of 440 cc., well within the ape range. It was not until other, adult, specimens were discovered in southern Africa during the next twenty years that Australopithecus africanus began to gain acceptance in the established scientific community.

7 Australopithecus africanus Sts 5 Mrs. Ples cranium ~ 2.5 MYA, the Australopithecus africanus Skull Sts 5 "Mrs. Ples" was discovered in 1947 by R. Broom and J. Robinson in Sterkfontein, Transvaal, South Africa. The discovery of this nearly complete cranium of a mature specimen led to a much more positive reception of South African australopithecines as hominins than Raymond Dart s description of the Taung juvenile skull, which he named Australopithecus africanus, but was broadly dismissed as a hominin. A. africanus shares several characteristics with later Homo and some distinctions from A. afarensis and other potentially early australopithecines. The Sts 5 cranial capacity is about 485 cc (A. africanus mean = 461 cc, range = cc). The base of the cranium is still relatively flat, but unlike previous australopithecines, it is much less pneumatized (fewer sinuses). The frontals (forehead) are more rounded, and the subnasal region is less prognathic (projecting). There is an absence of cranial crests, and changes in both the anterior dentition (front teeth), canines, and molars (see specimen STS. However, the front teeth are larger than in robust australopithecines. Originally thought by Broom to be a middle-aged female, Sts 5 is now considered by most to be a male.

8 Australopithecus africanus (Sts 52) partial maxilla (a) & mandible (b) MYA. Discovered by J.T. Robinson, in Sterkfontein, South Africa in The association of Sts 52a and Sts 52b seems reasonable based on the wear patterns and occlusion of the dentition. Sts 52a, which appears to be compressed laterally, represents part of the lower face. It possesses long, thin nasal bones, a relatively sharp lateral margin of the nasal aperture, a moderately long palate, which also may have been moderately wide (before compression), and an intraorbital region (space between the eyes sockets) that was likely not very broad. Most of the teeth in the maxilla, while slightly cracked, are relatively unworn. M3 is not completely erupted. The mandible is distorted, particularly on the right side. 52b, is a relatively small mandible for A. africanus, which generally are more heavily built than A. afarenisis. The body of the mandible is usually thicker and the symphysis (the front where the 2 halves of the mandible join) is much more reinforced. The ascending ramus (the part that articulates with the cranium) is broader and taller than in A. afarensis. A. africanus has smaller incisors (front teeth) and canines than previous australopithecines. However, the front teeth are larger than in robust australopithecines. The cheek teeth are larger than in A. afarensis but smaller than in the robust australopithecines. These dental changes are inferred to represent a reduced use of the anterior dentition (front teeth) and an emphasis on the molars, with associated changes in the chewing musculature.

9 Paranthropus boisei OH5 Zinjanthropus cranium 1.8 MYA. The Paranthropus boisei Skull, NUTCRACKER MAN, is the most famous fossil from Olduvai Gorge, Tanzania. OH 5 was discovered by Mary Leakey in 1959 and originally classified as Zinjanthropus boisei by L. Leakey in Nature later that year. The accepted genus name was later changed to Australopithecus, then recently renamed to Paranthropus a genus used by Robert Broom for the robust South Afican australopithecines. This discovery spurred paleoanthropology toward a modern, multidisciplinary approach, and focused paleoanthropologists' attention on East Africa. P. boisei's massive skull features a wide, concave face, enormous, flat molars (about 4 times as big as modern H. sapiens) and cranial adaptations for powerful chewing, hence its nickname, Nutcracker Man. The face is notably flatter than the older KNM-ER WT cranium. In contrast with the enlarged cheek teeth, the anterior dentition (front teeth) of P. boisei are much reduced in size. This combination of large chewing teeth and small anterior dentition is unlike any living ape. Note the sagittal crest and extremely large area for chewing muscle attachments on the zygomatic arch. The thick jaw allowed for the species' exceptional chewing capabilities. Cranial capacity of this individual is 530 cc, and P. boisei ranges between The morphology of P. boisei from east Africa is similar to that of P. robustus from South Africa. These are considered separate populations of successfully specialized australopithecines who persisted into the periods with the earliest representatives of the Homo line.

10 Paranthropus robustus SK 48 cranium 1.5 to 2 MYA. The Paranthropus robustus Skull SK-48 was discovered by Fourie in Swartkrans, South Africa in 1950 and described by R. Broom in SK-48, formerly called Paranthropus crassidens, greatly increased what is known about australopithecines. The Transvaal cave site where it was found was blasted by explosives but, remarkably, the skull survived. The skull was found with the right canine, the first premolar and all three molars intact. On the basis of the adult teeth and small sagittal crest, Broom determined the specimen to be an adult female. P. robustus has strong similarities to the east African group of robust australopithecines, P. Boisei. The probability that two populations persisted into periods when the earliest emergence of the Homo line is dated, suggests successful adaptations focused on processing course terrestrial foods, such as roots and tubers. Endocranial capacity estimates for P. robustus range from cc. Like the south African robust australopithecines, P. robustus has small, peglike anterior teeth and large molars. There is a pronounced sagital crest, visibly robust insertions for the muscles on the temporal bones (sides of the cranium), and the wide, flaring zygomatic arches (cheekbones) that accommodate large and powerful masseter chewing muscles. The maxilla and especially the mandibles of the robust australopithecines are very thick and deep. Both P. robustus and P. boisei exhibit craniofacial configurations that allowed tremendous vertical forces to be exerted between the maxillary (upper) and mandibular (lower) molars during mastication (chewing).

11 Homo habilis KNM-ER 1813 cranium 1.9 MYA. The Homo habilis Skull KNM-ER 1813 was discovered by K. Kimeu in 1973 at Koobi, Kenya, and described by R. Leakey in Nature in There is still controversy about this specimen's classification, with some scientists opting to classify it as an australopithecine and others believing it is a species of Homo. Some paleoanthropologists have raised the possibility that KNM-ER 1813 is the female counterpart to the Homo rudolfensis KNM-ER While dated to the same time period and sharing some characteristics, KNM-ER 1813 has a much smaller face, brain and teeth than Other paleoanthropologists argue that its brain size of 510 cc (in contrast to 1470's 750 cc) indicates a size difference too great to be due to sexual dimorphism and represents a separate species. This specimen is not simply a smaller, immature version of H. rudolfensis, as the third molar appears to have been worn down. The controversies about the taxonomy of Homo habilis may have less to do with identifying a consistent morphology as demonstrating that there may be significant and complex selective pressures on hominins at this time that result in the eventual selection of larger brained, tool-using hominins, who begin to emphasize a range of more complex cognitive capabilities.