More Important Topics of Cylinder

collection of bones at left, for example, can give a quite complete picture of how Australopithecus might have walked-a bipedal creature at the very dawn of man.

Many of the figures shown here have been built up from far fewer fragments-a jaw, some teeth perhaps, as indicated by the white highlights-and thus are products of educated guessing. But even if later finds should dictate changes, these reconstructions serve a purpose in showing how these creatures might have looked. When they lived can be seen from the geological time scale across the top-blue for the proto-apes, red and purple for the hominids and the first men, green for Homo sapiens.

Breaks in the ribbons signify extinction of a line or gaps in the fossil record. Although proto-apes and apes were quadrupedal, all are shown here standing for purposes of comparison. A spine, ribs and hip bones of Australopithecus reveal not only his approximate height and weight but, most important of all, his upright posture and bipedal gait.

Its rodent like characteristics may have contributed to the fact that Plesiadapis went extinct by the late Eocene and thus represents a sterile offshoot of the.

primate family tree. Rodents were undergoing their own radiation at this time and reproduce at a rate that a primate cannot compete with. Plesiadapis was competed out of the rodent niche by true rodents. It is in the early Paleocene that we first encounter animals in the fossil

record which show strong links to our own order, the primates. Surprisingly, early primate-like forms are best known from continents that are today, apart from their southernmost corners, not inhabited by primates other than human beings: Europe and North America. This unusual geographical occurrence can be

explained by the warm, even subtropical conditions that existed far into the north during Paleocene time. Favorable conditions also allowed other exotic animals like crocodiles to thrive at high latitudes. Yet the importance and diversity of primate-like

mammals in the Paleocene faunas of Europe and North America is remarkable. During the Paleocene most primate-like animals belonged to a group called Plesiadapiformes.

Traditionally, the plesiadapiforms have been regarded as archaic members of the order Primates.

Although plesiadapiforms are similar to modern primates in a number of characteristics of their skeleton, they were still on a much lower evolutionary level, comparable perhaps to the living tree-shrews.

Modern primates are unique among mammals in their adaptation to life in the trees. Their capabilities of grasping and leaping allow rapid locomotion in this environment, which is in turn related to the large brain size they have developed.

As far as we know, plesiadapiforms also spent most of their time in the trees. However, they lack adaptations for fast leaping as we see them in modern primates and were not capable of moving as quickly through the trees. In addition, their brain was still very small in comparison to modern primates.

On the other hand, plesiadapiforms soon acquired traits that are unusual for later primates, especially enlarged incisors that are superficially similar to those of rodents.

This suggests that the plesiadapiforms were not the direct ancestors of modern primates, but rather a branch that split off from the mainline of primate evolution (from today's point of view) at an early date. The picture is complicated by other still existing orders of mammals that must be close to primates on the evolutionary tree:

The tree-shrews (order Scandentia), the colugos or "flying lemurs" (order Dermoptera), and perhaps the bats (order Chiroptera), although the latter are only distantly related according to recent molecular studies.

Where plesiadapiforms fit in between all of these is still hotly debated. However, many scientists are today reluctant to call these archaic forms primates and regard them instead as members of a separate order Plesiadapiformes..

Tim White and associates have subsequently reassigned the hominid to a new genus, noting the apparently extreme dissimilarities between ramidus and all other known Australopithecines.

They proposed Ardipithecus (from "ardi", which means "ground" or "floor" in the Afar language) to be the genus [White, et al, 1995]. The initial and most extensive publication [White, et al, 1994] concerning Ardipithecus. ramidus specified that 17 hominid fossils had been located

by the end of 1993. These specimens were retrieved from a cluster of localities West of the Awash River, within the Afar Depression, Aramis, Ethiopia.

Hominid and associated fossil faunas, including wood, seed and vertebrate specimens, were found entirely within a single interval overlying the basal Gaala Tuff complex, and beneath the Daam Aatu Basaltic Tuff (these volcanic strata have produced dates of 4.389 and 4.388 million years, respectively) [Renne, et al, 1999]. This definitively places all Ardipithecine specimens just shy of 4.4 million years ago.

Additionally, the associated strata were most likely produced within the context of a heavily forested, flood plain environment. Evidence for this conclusion was derived from representative non-human fossil remains,

particularly from those species whose present-day analogues are environment-specific.

A morphological description of the initial, mainly dental, fossil remains of Ardipithecus ramidus was published by White et al, 1994. The physical attributes of this hominid show a range of primitive traits, which are most likely character retentions from the last hominid/chimpanzee ancestor.

At the same time, some hominid innovations are equally apparent. The currently known traits of Ardipithecus ramidus, in general, can be placed within two categories: ape-like traits and Australopithecine-like traits.

Much of the dentition is ape-like and this hominid most likely had a significantly different dietary niche than did later hominids. A small canine-incisor to postcanine dental ratio, typical of all other known hominids, is strikingly absent in Ardipithecus ramidus.

In addition to the presence of a relatively large anterior dentition, tooth enamel is thin. Though slightly greater than in teeth of modern chimpanzees, enamel thickness of A. ramidus is extremely thin by hominid standards.

Premolar and molar morphology also point to niche affinities with the great ape ancestors. Strong crown asymmetries, in particular enlarged buccal cusps, characterize the upper and lower premolars. Additionally, an ape-like molar shape prevails. The length (in the mesiodistal plane) to breadth (in the buccolingual plane) ratio, which is roughly equal to 1 in later hominids, is much greater in A. ramidus.

Some important derived features, link Ardipithecus ramidus with the Australopithecines. Hominid-like canines are present. These are low, blunt, and less projecting than the canines of all other known apes.

Upper and lower incisors are larger than those of the Australopithecines, but are smaller than those of chimpanzees. This character state can thus be considered transitional between apes and Australopithecines. Additionally, the lower molars are broader than those of a comparably-sized ape. This trait, too, approaches the common hominid condition.

Finally, something can be said of the skeletal anatomy and how it relates to the potentiality for bipedalism in A. ramidus. Pieces of the cranial bones that have been recovered, including parts of the temporal and the occipital, strongly indicate an anterior positioned foramen magnum.

The fact that the skull of A. ramidus rested atop the vertebral column, rather than in front of it, suggests that if this creature was not bipedal in the modern sense, it at least had key adaptations toward a similar end.

Scanty postcranial remains (most significantly, a partial humerus) indicate that A. ramidus was smaller in size than the mean body size of Australopithecus afarensis. However, this particular estimate falls within the range of variation of A. afarensis.

A mandible and partial postcranial skeleton of a single individual was found in 1994. Analysis and publication on this find has yet to be made. Once completed, this should provide significant insight into the positional repertoire of Ardipithecus ramidus, dispelling all doubt as to whether or not this truly was a bipedal hominid.

Renne, Paul R, Giday WoldeGabriel, William K Hart, Grant Heiken, and Tim D White (1999) Geological Society of America Bulletin, pp. 869-885. White, Tim D, Gen Suwa, and Berhane Asfaw (1994) Nature, 371:306-312. White, Tim D, Ben Suwa, and Berhane Asfaw (1995) Nature, 375:88.

This species was initially discovered (but not identified) in 1965, by a Harvard expedition led by B. Patterson. A distal end of a humerus (KNM-KP 271) was recovered from a site on the west side of Lake Turkana in Kenya, a site called Kanapoi.

For years the specimen's species was debated by those who saw it as Australopithecus, due to its age of approximately 4 myr, and those who saw it as Homo. Fieldwork was not conducted at the site for nearly 30 years, until work began by Meave Leakey et al.

The renewed work provided dates, faunal remains, environmental reconstruction, and nine new hominid specimens. The material was given the name Australopithecus anamensis, because of several important differences with A. afarensis that seem to distinguish it as a separate species. An additional twelve fossil specimens from Allia Bay, on the eastern shores of Lake Turkana,

has also been placed within the species anamensis along with the Kanapoi material. The strata from which this material was recovered has been well-dated with the Ar-Ar method, and there are two well-defined levels: an earlier (4.17-4.12 mya) and a later (4.1-3.9 mya) level.

Material from the lower level includes the type mandible for the species (KNM-KP 29281) with an associated portion of the left temporal bone thought to be female, an almost complete maxilla (KNM-KP 29283), and a second recently discovered maxilla with parallel postcanine tooth rows.

Specimens from the upper level include a partial toothless mandible (KNM-KP 29287) with a much larger canine root and a more vertically inclined symphysis than the KP 29281 female, a tibia lacking its diaphysis (KNM KP 29285), and the original distal humerus (KP 271).

Specimens from other sites such as Sibilot Hill also may be anamensis, but there is much debate on the validity of the anamensis species, since the samples are very close in morphology to afarensis.

One factor that seems to separate anamensis and afarensis is the mean body weight of the male specimens. The mean of Hadar afarensis specimens is 44.6 kg, but the body weight estimates for the tibia (KP 29285) is approximately 55 kg, and approximately 58 kg for the humerus (KP 271).

These weights were estimated using McHenry's predictive regression equations. This is a very small sample to draw conclusions from, but there is a difference of nearly 20% between the anamensis and afarensis samples. Dental materials seem to show that the females, however, were close to the Hadar samples, meaning that the anamensis species was fairly dimorphic.

The anamensis species seems to have been an obligate biped, as shown by the tibia and a hallux bone recovered: KP 29285 has a rectangual proximal surface with anterior-posterior lengthening of the proximal articulation. KP 29285 has concave condyles of approximately equal area (in chimpanzees one of the condyles is convex). Has flat larger lateral condyle.

There is less space between tibia and fibula than in chimps. There is thickened cortical bone at the proximal and distal ends. The shaft of the tibia ia straight. There is a directly inferior orientation of the distal articular surface. A hallux (big toe) was recovered, which showed evidence for the hallucial flexors.

A radius recovered shows that anamensis was powerfully built, but does not show evidence of weight bearing.

The dental remains show strong similarites to A. ramidus, however the Kanapoi material differs in several important ways that distinguish it as a separate species (separate from ramidus, if not also afarensis).

There is a stronger adaptations to powerful masticatory forces, the postcanine teeth are larger than in ramidus, and there is absolutely and relatively thicker enamel. Details of the mandibular fossa and the surrounding region of the cranial base also differs from the Aramis material.

For example, the tympanic tube does not extend as far laterally, relative to the mandibular fossa. For these reasons, the Kanapoi materials deserve a distinct species name. The dental traits of anamensis includes: Has an elongated, posteriorly angled mandibular symphysis.

Has an elongated surface at the front of the mandible, behind the incisors (postincisive plane).

A shallow palate. Large, elongated canines. Vertical maxillary canine roots. Strongly asymmetric P3. The upper molars are broader across the mesial sides. There is thicker molar enamel.

Features shared with the Aramis samples include: An absolutely and relatively small P4 (it is unusual in the hominids that they are smaller than P3. The deciduous molars are elongated with thin enamel. The tooth rows are straight, parallel, and close together.

There is a particularly small opening of the auditory meatus (within the Hadar range, but just barely). There is some question as to whether the Kanapoi material deserves a separate species name, or whether the material should be subsumed under afarensis. The morphology is very similar, but Leakey and A. Walker give several reasons why they believe this is a new species:

The upper canine root is bigger and less posteriorly inclined.

The upper molars have more sloping lingual sides (but this is a very subtle difference).

The lower molars have more sloping buccal sides (but this is not really another reason since this is codependent with the angling of the upper molars). The mandibular symphysis retreats more (but this is very questionable because all specimens do not have this feature, and this is a highly variable trait).

It seems fairly reliable to distinguish the Kanapoi material from A. ramidus, however, it is highly questionable that this material is a separate species from A. afarensis. This will undoubtedly be debated until more specimens are obtained and a clearer comparison between samples can be made.

In any case, the similar but more primitive anatomy of anamensis relative to afarensis make it a good candidate for a precursor to afarensis. Whether a precursor species or simply part or a highly variable population through time is a matter of some debate. I personally follow the ideology that is it ok to name new species for disputed specimens, since this designation can be changed in the future if needed.

As long as the genus name is held constant in these related specimens, it is ok to separate into different species, since this seems to keep study of specimens current, and they are not simply tagged with a known taxonomy and little studied.

approximately 2.5 myr. The type specimen of the species is BOU-VP-12/130, an associated set of cranial fragments comprising the frontal, parietals, and maxilla with dentition.

The specimen was discovered by Y. Haile-Selassie on November 20, 1997, and the word garhi means "surprise" in the local Afar language.

These specimens are important no matter what the eventual final attribution, due to the fact that the remains are from East Africa at a time when there is very little remains (2.0-3.0 myr).

One of the more striking features of the A. garhi remains is the size of the postcanine dentition, which is at or beyond the nonrobust australopithecine or A. robustus extremes. This is the only feature that suggests any link to the robusts, and as such it is very unlikely that the specimen is in any way derived from or a sister species to robustus.

This is seen especially in the large size of the anterior teeth, exceeding those of the largest australopithecines and far exceeding the robusts, who are marked by anterior tooth reduction or stasis.

Based on tooth size, the garhi material seems to fit well with schemes that see either one or both of africanus and afarensis as a direct human descendent, as the canine-to-premolar/molar size ratios are comparable to both species and early Homo.

The cranial attributes do not seem to directly make an attribution or negate the possibility of attribution to a specific phylogeny, but this may do with the sparse nature of the remains and the small sample size (the small sample size must be kept in mind of any phylogenetic discussion based on the described traits). Specific cranial attributes include:

The lower face is prognathic with procumbent incisors. Canine roots are placed well lateral to the nasal aperture margin. The premaxillary surface is separated from the nasal floor by a blunt ridge and is transversely and sagittally convex. The palate is vertically thin.

The zygomatic roots originate above P4/M1. The dental arcade is U-shaped, with slightly divergent dental rows. The temporal lines encroach deeply on the frontal, past the midsupraorbital position and likely met anterior to bregma. The postglabellar frontal squama is depressed in a frontal trigon.

The localized frontal sinus is limited to the medial one-third of the supraorbital surface. There is marked postorbital constriction. The parietal bones have a well-formed, bipartite, anteriorly positioned sagittal crest that divides above lambda. Cranial capacity of approximately 450 cc (reconstructed).

There is not much to conclude at this point, merely to explain what the researchers hypothesis as the possible phylogenetic relationship of A. garhi. The researchers discuss the idea that garhi represents a direct ancestor of modern humans that is derived from africanus which is likely derived itself from afarensis.

This does fit in with Wolpoff's idea of an unidentified late africanus group with many robust features, but know one can say with any certainty at this point. The specimens may even be attributed to Homo rather than Australopithecus. All that can be done now is to watch what unfolds.

For its antiquity, A. afarensis is one of the better known

species of early human, with specimens collected from over 300 individuals.

It is a species that exhibits many cranial features which are reminiscent of our ape ancestry, such as a forward protruding (prognathic) face, a "U-shaped" palate (with the cheek teeth parallel in rows to each other similar to an ape) and not the parabolic shape of a modern human, and a small neurocranium (brain case) that averages only 430cc in size (not significantly larger than a modern chimpanzee).

The specimens recovered have given representative examples of almost all of the bones of the A. afarensis skeleton. From this, it is clear that there are many significant difference between A. afarensis and its ape predecessors, one of which is crucial to later human evolution, bipedality.

The position of A. afarensis in the phylogeny of early humans is under debate. Many feel that it is ancestral to the east African "robust" early humans, and possibly to all robust forms. Additionally, A. afarensis is proposed as the ancestor to later Homo.

Olduvai (which had been relatively fruitless over the previous 30 years), which led to renewed research interest in the area, added an important stage in a relatively sparse hominid lineage at the time, and

also was important in focusing attention on multidisciplinary research.

The fairly complete cranium (sans mandible) was given the species name Zinjanthropus boisei by Louis Leakey, which eventually became known as Australopithecus boisei. However, Zinjanthropus lives on in the well known nickname of OH 5, "Zinj".

Specimens attributed to A. boisei have been found mostly in Ethiopia, Tanzania, and Kenya in East Africa. The oldest has been found at Omo, Ethiopia, dating to approximately 2.3 myr (L. 74a-21), and the youngest has been found at Olduvai Gorge, dating to approximately 1.2 myr (OH 3 and OH 38).A. boisei seems to be the end point of a lineage that that was adapted to high masticatory stress needed to deal with hard low-quality foods.

This species is sometimes called "hyper-robust" due to the relative and absolute size of their postcanines. This lineage may have died out due to overspecialization to a specific environment, and when the environment changed, evolution could not keep up. This seems to be the generally accepted idea regarding boisei, and there seems little hard evidence to contradict it.

The most striking feature of the A. boisei specimens is the degree of megadontia. This species has the absolute largest teeth found in any hominid group, with teeth similar in size to gorillas (who weigh as much as 10 times as much). They are often referred to as hyper-robust due to the massive postcanine megadontia.

The features of boisei are best described in relation to the other "robusts" (including aethiopicus), since this best shows some of the features that exclude aethiopicus from the "robust" lineage in favor of africanus. Features that line up boisei as a descendent of africanus rather than aethiopicus include:

The face is more vertically set, more orthognathic (variability in this trait).

There is anterior teeth reduction. There is a continued increase in postcanine teeth size. There is a larger cranial capacity (500-550 cc). The sagittal crest is on the mid-brain case, not the posterior.

Since aethiopicus and africanus are contemporary, only one can be the ancestor to boisei, and africanus seems a more likely scenario. Perhaps more importantly, boisei shares unique traits with later species that undoubtedly link it with africanus (who is likely the ancestor of these later species). Features that link boisei with A. robustus (and possibly early Homo) include:

Some structural brain differences reflected in endocasts, such as: A) greater frontal lobe breadth B) expanded parietal cortex C) increased cerebral height (high cerebral to cerebellar height) D) cerebellar lobes "tucked in" and not projecting laterally or posteriorly. Increased flexion of the cranial base.

Shortening of the base and decrease in the angle of the petrous pyramids. More anterior foramen magnum position. Deeper mandibular fossa with well-delineated, projecting, articular eminence. Nearly horizontal orientation of nuchal plane.

Expanded height of occipital plane of the occiput, with a concomitant low inion position. Decreased facial prognathism, especially subnasal. Shortened distance between the tooth row and the mandibular fossa. Reduced posterior component of temporalis muscle.

Weakly developed or absence of pneumatized bone in the temporal squama. The hyper-robusticity of boisei did not extend to their body size, as they are approximately only 10% larger than africanus (and a whopping 60% smaller than aethiopicus). A. boisei also shows a progression toward a more modern form relative to its ancestors, as sexual dimorphism is reduced (with males 1.3 time larger than females).

A. boisei was very important in clearing up a controversy that raged in the 1960s over the idea of the "Single Species Hypothesis" (championed by University of Michigan professor Milford Wolpoff). The single species hypothesis states that every environmental niche can only support one species, and that in hominids, "monkey-see monkey-do" holds true.

Thus, if contemporary hominid groups came into contact, they would have the same behaviors, would attempt to fill the same niche, and conflict would ensue with one species the evolutionary victor, and one the loser (or would create an atmosphere where multiple hominid groups could not arise, due to the competition).

It was argued that the known remains belonged to a single sexually dimorphic species, with the males attributed to robustus, and the females attributed to africanus. The discovery of boisei of both sexes in the same site, dated to the same time, showed that even if the South African material was a single sexually dimorphic species, boisei was a different species contemporary with it, bringing into doubt the validity of the single species hypothesis.

It is now generally accepted that (in the instance of the South African australopithecines) there is two separate species, and not a single sexually dimorphic one. While some claim that this was the "death" of the single species hypothesis, it really only showed that two different species could be contemporary, and modified single species concept (one highly variable population concept) is alive and well, and difficult to prove or disprove, which guarantees it will be around and debated for a long time to come.

Australopithecus boisei is an important species both in the history of paleoanthropological research and in constructing the phylogeny of the hominid lines. The features it shares or lacks with contemporary and earlier species makes relatively clear the relative phylogeny of the "robust" australopithecines.

It also is present at a time when stone tools become much more common, and may have even made and used some. In the end, however, it seems that boisei became too specialized, and died with climatic and/or environmental shifts.

The standard line at the time by some of the powerful figures in the field (e.g., A. Keith and O. Abel) was that the ancestors of humans should be found in Europe, and should have an enlarged brain and an apelike jaw (as was the case in the Piltdown Man hoax).

The claim that the specimen was a hominid was rejected by those who saw the material as that of a young chimpanzee or gorilla.

This view was not helped by the difficulty in acquiring casts, the material was distant from many in the field (few of which ever travelled to actually view the material), and most importantly, was that of a juvenile. Juveniles are often misrepresentative of adult states, and most researchers claimed that the Taung Child would have developed into a chimpanzee or gorilla ancestor.

Due to the hostile or indifferent response of his peers, Dart

never followed up the find with further excavations, and no other specimens of the species have been found at Taung. Dart dedicated himself to developing the anatomy department at the University of Witwatersrand, and it would be twenty years later when sites like Sterkfontein were found that corroborated Darts ideas.

Though the genus designation mixed both Latin ("australo") and Greek ("pithecus"), the genus name has become accepted as the label by which the group of pre-Homo hominids in Africa have come to be known. Dart claimed that A. africanus was bipedal due to the position of the foramen magnum, and was vindicated by later finds, such as STS 14, which showed unequivocally that africanus was an obligate biped.

The earliest africanus material comes from sites such as Sterkfontein, Makapansgat, Gladysvale, and Taung. This material dates to the end of the Early Pliocene, mostly between 2.9-2.4 myr, with the Sterkfontein Member 2 material (possibly afarensis or other species) being the earliest known possible africanus, dating to about 3.5 myr. The Sterkfontein material are problematic,

as there may be intrusions from later strata, and there is a heterogenous mixture of earlier and more modern faunal species, and thus, this material may be as young as 1.0 myr.

Most postcrania material attributed to africanus is well within the range of variation of the afarensis material, however, the limb proportions may be different. STS 14 is a 2.5 myr old specimen from Sterkfontein. This specimen is particularly important as it includes both os coxa, as well as many of the vertebrae.

This find showed unequivocally that these hominids were bipedal, and were not simply apes, vindicating Raymond Dart. Features of STS 14 that align it with a more humanlike locomotor capacity include: The iliac blade is short and wide.

There is a well-developed sciatic notch. There is a strong anterior inferior iliac spine.

STS 14 has six lumbar vertebrae (whereas modern humans have five, and chimps usually have three). With an increased number of lumbar vertebrae (the ancestral condition, as in cercopithecoids), bipedalism may have been the ancestral condition (from a very small-bodied primate?). While it is ver similar in morphology (relative to its size), there are also differences.

This specimen differs from modern human in that: There is a forward projecting anterior superior iliac spine. A very small articular surface for the sacrum. A marked outward flare of the iliac blades. There is a fairly large sample of africanus teeth known (though not as large a smaple as the afarensis material).

The material shows several important differences when compared to afarensis that include: Postcanine teeth are larger, more bulbously cusped, and relatively broader (the size difference is greater in the later erupting teeth of each type), and may have somewhat thicker enamel, especially on the tooth walls. Dm1 is larger and more squared, with more equal sized cusps.

The anterior lower premolars are always bicuspid, usually with equal or close to equal sized cusps, and wear more similarly to the other premolars. The anterior lower premolars have greater enamel thickness. Compared intrasex, the africanus central incisors show no reduction but the other anterior teeth are usually smaller.

The ranges almost completely overlap, however, and there are very large canines and incisors in both samples. No canines wear to have cutting edges (canine-premolar diatemata are rare), even though a few are large enough to project beyond the level of the other teeth (this is much more common in the afarensis sample).

Although the canines are reduced compared with the earlier Plocene samples, their roots -especially those of the maxilla teeth - are still long and robust. The canines also wear more rapidly than the afarensis material, with the wear almost always on the tips. There is significant sexual dimorphism in the canines, although not as much as any of the apes, while there is sexual dimorphism on the level of gorillas in the postcanine material.

This pattern of big teeth seems to have been influenced by the africanus diet and chewing pattern. A. Walker and M. Wolpoff claim that the africanus chewing pattern is similar to modern hunter-gatherer groups, with the molars and premolars designed to last a lifetime of wear and tear (the oldest individuals dying at about the time they have no crowns left in their mouth - max age about 35).

The diet of these South African hominids seems to have been seasonal, with emphasis on a frugivory diet, with much seeds and other hard objects being masticated.

There is a good sized sample of africanus crania, allowing reasonably strong comments to be made on the materials affinities to other material. Some of the better-known specimens include STS 5 (Mrs. Ples), a 2.5 myr cranium of an adult male with a brain about 485 cc, STS 71, a 2.5 myr male partial cranium with an estimated 428 cc brain, STW 505, an indovidual with a brain esimated to have been 625 cc, and the type specimen of africanus, the Taung Child.

The facial features of the africanus material are a mixture of more modern and archaic ones, with similarity to (and important differences between) the afarensis material.

Some of these features (relative to afarensis include: Retraction of the palate from a position in front of the face to under it. Forward shift of the zygomatic processes of the maxilla, the zygomatic bone, and the front of the masseter muscle, creating the zygomatic prominence.

Expansion of the anterior part of the temporalis muscle. A broader nasal aperture.

Anterior pillars extending above the canine roots, of variable expression creating thickened lateral nasal margins. Structural changes in the jaw related to expanding premolars and molars, as well as incisor and (especially) canine reduction and decreased emphasis on anterior loading.

The africanus material is seen as different things by different people. Some see this as a regional variation or subspecies of afarensis, some see it as two completely different species, and some consider the africanus material to be the descendants of afarensis.

Another important question that has been, is, and will probably always be debated is the question of whether the africanus material represents two or more species, a sexually dimorphic species, or a very variable species (especially with regards to inter-era speculation).

The accepted view seems to be that they deserve separate species status due to both their differences from the afarensis material and their geographic separation from them. However, a very important question in debate is whether or not this species contributed to the modern human lineage.

This hominid status is predicated upon a few teeth, some fragments of jaw and a palate unmistakably human in

shape. The direct lineage from the ancestor of both man and the modern apes to modern man is not known.

Evidence is increasing. Thousands of relics fit the general pattern.

The word hominidae is used to describe the total member species of the human family that have lived since the last common ancestor of both man and the apes. A hominid is an individual species within that family.

The field of science which studies the human fossil record is known as paleoanthropology. It is the intersection of the disciplines of paleontology (the study of ancient life forms) and anthropology (the study of humans).

Each hominid name consists of a genus name (e.g. Australopithecus, Homo) which is always capitalized, and a species name (e.g. africanus, erectus) which is always in lower case.

Some controversy exists on the time of this common ancestor to both ape and human, but it is believed to be about 5.5 million years ago. A key fossil record near that time is Ramapithecus, which was believed to be an early hominid for many years, but is now considered an ancient ape that lived near the fork in our common lineage. Ramapithecus is now thought to be an ancestor of the modern apes.

From a genome viewpoint, the difference between modern man and the modern apes is quite small, about 2 percent. From a physical viewpoint, the greatest difference is in locomotion.

The human walks upright. It is generally thought that this came about when the ancient hominid adopted the edge of the forest and plain and adapted to a life under the trees as opposed to in them.

Fossil evidence shows that this bipedal adaptation was completed quite early, perhaps as early as four million years ago, long before we looked like or thought like we do today. Facial feature changes toward the modern appearance came much later. The facial characteristics of modern man are about 100,000 years old. The faces of earlier hominid were much more apelike.

he shape and the size of the molar convinced Broom that this was a different species than A. africanus (Broom's transvaalensis), and upon further investigation, found that the specimen had been found by a young boy who worked in the cave as a guide on Sundays.

Broom searched for the boy (Gert Terblanche) and found him at school. Broom lectured the boy's class on the cave sites of the area, and was then led to the place of the

specimen's discovery, Kromdraai. Broom found several more cranial and mandibular fragments associated with the original maxillary specimen, and this partial cranium (TM 1517) became the type specimen for A. robustus.

Broom spent some time working on a monograph of the australopithecines, which was published in 1946. This monograph included the description of TM 1517, and was a turning point for the South African australopithecines in the eyes of the world.

The monograph received the U.S. National Academy of Sciences award for the most important book of the year in biology, and along with L Gros Clark's published approval of the South African australopithecines as hominids, was very important in altering the view that the South African specimens were human ancestors and not simply an ape.

Another important find was SK 6, a portion of mandible and several teeth. Another discovery of Broom's, he originally named a new species on it (Paranthropus crassidens). However, the specimen is generally accepted as robustus, though it is also considered a type specimen because of this separate species designation.

One of the more complete robustus specimens is SK 48, a fairly complete crania of what is probably a female. This specimen - due to its completeness - added much information on the cranial characteristics of the robust australopithecines.

One specimen may or may not be robustus, since it was found at Sterkfontein, and the presence of robustus and africanus in the same place at basically the same time would cause some phylogentic attribution of the robust australopithecines major problems.

STW 252 is considered by those who see more than one species at Sterkfontein as robustus, and as africanus by those that see one species. The dentition seems to indicate inclusion in robustus, but the uncertainty of the date causes some to view it cautiously.

The A. robustus remains generally are from three sites: Swartkrans, Dreimulen, and Kromdraai (with the aforementioned Sterkfontein specimen possibly included). By far the largest of these sites is Swartkrans. One of the major problems with these South African sites is dating, but generally, robustus remains can be safely placed from 2.0-1.0 myr, and possibly even earlier.

The dating of these sites is crucial to understanding the phylogeny of the robust australopithecines, but for now, the dates are somewhat in question. An understanding of the characteristics of robustus can best be seen by comparing them to an earlier specie (africanus) and a penecontemporary one (boisei).

The robustus crania are many, but fragmentary, with a known cranial capacity for just one individual specimen, SK 1585, an endocast with a 530 cc capacity. There is evidence of significant expansion over africanus, with an estimated 15% average increase in brain size over africanus.

The sexual dimorphism level of about 20% seems to be basically unchanged. In his analysis of SK 1585, R. Holloway concluded that robustus shows a general trend towards a more modern brain - similar to that of boisei - over that of africanus. These modern trends include:

Some structural brain differences reflected in endocasts, such as: A) greater frontal lobe breadth B) expanded parietal cortex C) increased cerebral height (high cerebral to cerebellar height) D) cerebellar lobes "tucked in" and not projecting laterally or posteriorly.

Increased flexion of the cranial base. Shortening of the base and decrease in the angle of the petrous pyramids. More anterior foramen magnum position. Deeper mandibular fossa with well-delineated, projecting, articular eminence. Nearly horizontal orientation of nuchal plane. Expanded height of occipital plane of the occiput, with a concomitant low inion position.

Decreased facial prognathism, especially subnasal. Shortened distance between the tooth row and the mandibular fossa. Reduced posterior component of temporalis muscle. Weakly developed or absence of pneumatized bone in the temporal squama.

The increase in body size over africanus is minimal, which means that there is significantly increased encephalization, rather than simply an allometric increase with increased body size.

The remains from Swartkrans are very variable, but seem (compared to africanus) to have more robust crania, with better developed muscle markings, more prominent tori, and thicker buttressing structures. Like the earlier specimens, these features are on a fairly thin cranial vault.

The cranial bases seem to differ, but the preservation makes comparisons difficult, with only one unambiguously preserved specimen (SK 47). What evidence there is seems to indicate that the Swartkrans hominids have a broader and shorter (more Homo-like) cranial bases with a more anterior foramen magnum position, and a petrous bone that is more transversely oriented than in earlier australopithecines.

The amount of basicranial flexion seems moderate (more than africanus, less than boisei). However, these observations are made unclear due to the specimen being a juvenile, but the 495 cc cranial capacity is close to the female mean, and there likely would have been little change.

A. robustus continues the trends seen in africanus with regards to facial changes, but remains very similar (and distinct from boisei). These features include:

The two species are equally prognathic.

Both have nasal bones that are the same size and shape.

Both have anterior pillars that border the nasal aperture, extending upward from the buttresses for the canine roots.

Both have a lower border of the cheek that is virtually a straight line from its origin on the side of the palate, extending to the base of the zygomatic arch, which is the widest portion of the face.

There is substantial increases in postcanine tooth size (though not at the level of boisei), with increases in both absolute and relative size over africanus. The canines seem to have changed little, while the incisors decreased in size significantly, possibly due to overcrowding, as there is overlap of anterior teeth in 43% of the Swartkrans remains.

The increase in postcanine tooth size includes an increase in enamel thickness, and while this has been interpreted in various ways, the idea that robustus was an herbivore/frugivore that subsisted on hard gritty nuts and plants (J.T. Robinson's dietary hypothesis) seems to be in serious doubt, with an eclectic omnivorous diet seems to be more likely due to recent work determining low strontium/calcium ratios, and C4 contribution (likely from eating grazing animals).

Postcranial evidence shows little difference between robustus, africanus, or boisei. They were all small-bodied obligate bipeds, that used an efficient walking gait.

The main question regarding A. robustus seems to be the question of whether or not it is a separate species from A. boisei, or if they are geographic species of a wide-ranging variable population.

Most researchers seem to agree that they are separate lineages, with several important evolutionary trends that distinguish them. However, they share even more of the same evolutionary trends. It seems safe to call these separate lineages, but a vocal protest exists among those who see a monophyletic lineage (re: Paranthropus).

Very little is known about Australopithecus aethiopicus, since so few specimens have been attributed to the species, but the features that are known provide important

insights into the possible evolutionary history between the "robust" and "gracile" australopithecines. In general, aethiopicus shows a mixture of both primitive and derived features, and dates to a time that makes it important

in the its placement into the hominid phylogenetic tree.

The first specimen attributed to this species group is an edentulous mandible (Omo 18) found in southern Ethiopia, west of the Omo River, in 1967. The specimen was discovered by a French expedition led by Camille Arambourg and Yves Coppens.

This 2.5 million year old mandible was placed into a new species by its discoverers, who named the species Paraustralopithecus aethiopicus. They believed that the specimen deserved a new species designation because its V-shaped jaw (among other features) distinguished it from the robust australopithecus forms known in the area. Generally, the discovery and designation was ignored by the majority of paleoanthropologists.

Not until the Black Skull discovery was there much interest in the specimen, but once KNM-WT 17000 was discovered in, interest was renewed in the Omo mandible. The genus name was dropped in favor of the more traditional Australopithecus designation, but Arambourg and Coppens' species designation of aethiopicus was taken as the species name.

This species designation is still debated by many who see the remains of early robustus or an early precursor, and those who see aethiopicus as proof that africanus is not the forerunner of all the "robusts".

The better known aethiopicus specimen is KNM-WT 17000, a nearly complete skull sans the mandible. The specimen is known as the "Black Skull" because mineral uptake during fossilization gave the specimen a blue-black color. The specimen was discovered in a 2.5 myr deposit west of Lake Turkana, and through a wrench in many evolutionary schemes accepted by many researchers.

The specimen is similar to a male A. afarensis, but with a very small cranial capacity (410 cc), and an even more powerful nuchal musculature and very developed masticatory apparatus. The well-developed masticatory features are seen by:

The large palate with a thick roof.

The broken roots of large rooted (and thus probably large crowned) molars and 4th premolar.

The very anterior zygomatic process of the maxilla whose size and orientation creates a flat, flaring face (this puts the masseter attachment far forward and lateral, where its leverage in producing grinding motions is best).

The skull does not retain any teeth, but the size of the roots and the palate indicate that the anterior and postcanine teeth were very large. Other specimens attributed to aethiopicus show thickened molar enamel (similar to afarensis).

The combination of a very small brain and enlarged masticatory apparatus leads to the development of a well-developed sagittal crest that meets the nuchal crest to form a compound temporonuchal crest similar to A. afarensis at the rear of the vault. Other features that resemble A. afarensis include: Large anterior tooth sockets.

A flattened cranial base (and flattening of everything on it such as the flat, nonprojecting articular eminence of the mandibular fossa and the shallow palate).

A posterior foramen magnum position and more sagittal orientation of the petrous pyramid of the temporal bone. Extreme development of the nuchal muscles and the more vertical orientation of their attachment of the occiptal bone.

Extreme facial prognathism.

Other remains were attributed to aethiopicus following KNM-WT 17000, including Omo 338y-6. The is the 2.39 myr remains of a 10-year-old juvenile vault that lacks the frontal bone and the face.

This juvenile specimen shows the early formation of a powerful masticatory system. Features that indicate this include:

The temporal lines meet at the middle in an anterior position (there would have been a sagittal crest if the organism had lived long enough). A marked development of the superior nuchal line with a strong downward projecting inion at its center. A large overlap of the temporal onto the parietal bone.

The earliest known aethiopicus material is probably the 2.7 myr L55s-33 mandible fragment from level C6 in the Omo deposits, north of Lake Turkana. L55s-33 is the front portion of a mandible that retains most of a worn P4 crown.

This specimen was generally not attributed to a species until the Black Skull find, since the diagnostic tooth was too small to be A. boisei (83% the size of the smallest known boisei tooth), but did nto fit into any other species well. G. Suwa, who has specialized in the analysis of australopithecine premolars, reported that the premolar was unusually thick-enameled and had the squared-off shape of the hyper-robust species.

He was unable to attribute the premolar to a species, and placed it in an unspecified robust australopithecine other than boisei. It now seems that he was right and the material belongs to A. aethiopicus.

Australopithecus aethiopicus became important in phylogenetic considerations soon after the discovery of the Black Skull. The species is generally accepted to have shown that the genus designation Paranthropus is polyphyletic and invalid, though some still vocally argue against that fact.

One of the earliest important cladistic analysis was by Walker and Leakey (1988), which they claim shows aethiopicus is at the base of the boisei lineage, is more primitive than robustus, and that aethiopicus is not ancestral to robustus. However, Strait et al. says that this phylogeny requires 39 extra steps above the most parsimonious tree, and most cladists do not favor this phylogeny.

Skelton and McHenry (1992) and Lieberman et al. (1996) both came to the same conclusions regarding aethiopicus and Paranthropus using different character traits.

Both see aethiopicus as a dead-end sidebranch and Paranthropus as polyphyletic and invalid. On the other side of the coin, Strait et al. (1997) see all the robusts sharing a recent common ancestor (aethiopicus), with Paranthropus monophyletic.

Lucy was found by Donald Johanson and Tom Gray on the 24th of November, 1974, at the site of Hadar in Ethiopia.

They had taken a Land Rover out that day to map in another locality.

After a long, hot morning of mapping and surveying for fossils, they decided to head back to the vehicle. Johanson suggested taking an alternate route back to the Land Rover, through a nearby gully.

Within moments, he spotted a right proximal ulna (forearm bone) and quickly identified it as a hominid. Shortly thereafter, he saw an occipital (skull) bone, then a femur, some ribs, a pelvis, and the lower jaw. Two weeks later, after many hours of excavation, screening, and sorting, several hundred fragments of bone had been recovered, representing 40% of a single hominid skeleton.

How did Lucy get her name?

Later in the night of November 24th, there was much celebration and excitement over the discovery of what

looked like a fairly complete hominid skeleton.

There was drinking, dancing, and singing; the Beatles' song "Lucy in the Sky With Diamonds" was playing over and over. At some point during that night ­ no one remembers when or by whom ­ the skeleton was given the name "Lucy." The name has stuck.

How do we know she was a hominid? The term hominid refers to a member of the zoological family Hominidae. Hominidae encompasses all species originating after the human/African ape ancestral split, leading to and including all species of Australopithecus and Homo. While these species differ in many ways, hominids share a suite of characteristics which define them as a group. The most conspicuous of these traits is bipedal locomotion, or walking upright.

How do we know Lucy walked upright?

As in a modern human's skeleton, Lucy's bones are rife with evidence clearly pointing to bipedality. Her distal femur shows several traits unique to bipedality. The shaft is angled relative to the condyles (knee joint surfaces) which allows bipeds to balance on one leg at a time during locomotion. There is a prominent patellar lip to keep the patella (knee cap) from dislocating due to this angle.

Her condyles are large, and are thus adapted to handling the added weight which results from shifting from four limbs to two. The pelvis exhibits a number of adaptations to bipedality. The entire structure has been remodeled to accommodate an upright stance and the need to balance the trunk on only one limb with each stride.

The talus, in her ankle, shows evidence for a convergent big toe, sacrificing manipulative abilities for efficiency in bipedal locomotion. The vertebrae show evidence of the spinal curvatures necessitated by a permanent upright stance. How do we know she was female?

Evidence now strongly suggests that the Hadar material, as well as fossils from elsewhere in East Africa from the same time period, belong to a single, sexually dimorphic species known as Australopithecus afarensis. At Hadar the size difference is very clear, with larger males and smaller females being fairly easy to distinguish. Lucy clearly fits into the smaller group.

How did she die?

No cause has been determined for Lucy's death. One of the few clues we have is the conspicuous lack of post-mortem carnivore and scavenger marks. Typically, animals that were killed by predators and then scavenged by other animals (such as hyaenas) will show evidence of chewing, crushing, and gnawing on the bones.

The ends of long bones are often missing, and their shafts are sometimes broken (which enables the predator to get to the marrow). In contrast, the only damage we see on Lucy's bones is a single carnivore tooth puncture mark on the top of her left pubic bone. This is what is called a peri-mortem injury, one occurring at or around the time of death.

If it occurred after she died but while the bone was still fresh, then it may not be related to her death.

How old was she when she died?

There are several indicators which give a fair idea of her age. Her third molars ("wisdom teeth") are erupted and slightly worn, indicating that she was fully adult. All the ends of her bones had fused and her cranial sutures had closed, indicating completed skeletal development.

Her vertebrae show signs of degenerative disease, but this is not always associated with older age. All these indicators, when taken together, suggest that she was a young, but fully mature, adult when she died.

Where is the "real" Lucy?

IHO has replicas of Lucy's bones which were produced in the Institute's casting and molding laboratories. The "real" Lucy is stored in a specially constructed safe in the Paleoanthropology Laboratories of the National Museum of Ethiopia in Addis Ababa, Ethiopia.

Because of the rare and fragile nature of many fossils, including hominids, molds are often made of the original fossils. The molds are then used to create detailed copies, called casts, which can be used for teaching, research, and exhibits.

How old is Lucy?

The hominid-bearing sediments in the Hadar formation are divided into three members. Lucy was found in the highest of these -- the Kada Hadar, or KH -- member. While fossils cannot be dated directly, the deposits in which they are found sometimes contain volcanic flows and ashes, which can now be dated with the 40Ar/39Ar (Argon-Argon) dating technique.

Armed with these dates and bolstered by paleomagnetic, paleontological, and sedimentological studies, researchers can place fossils into a dated framework with accuracy and precision. Lucy is dated to just less than 3.18 million years old.

How do we know that her skeleton is from a single individual?

Although several hundred fragments of hominid bone were found at the Lucy site, there was no duplication of bones. A single duplication of even the most modest of bone fragments would have disproved the single skeleton claim, but no such duplication is seen in Lucy.

The bones all come from an individual of a single species, a single size, and a single developmental age. In life, she would have stood about three-and-a-half feet tall, and weighed about 60 to 65 pounds.