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Prehistoric World

Hominid Chronology

by Peter Kessler, 26 July 2005. Updated 8 January 2017

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A SEVEN PART FEATURE:
Part 1: 20 million years
Part 2: 3.9 million years
Part 3: 2.3 million years
Part 4: 1.9 million years
Part 5: 600,000 years
Part 6: 350,000 years
Part 7: 200,000 years

 

Mother of Man
 

3.9 million

Australopithecus afarensis
Part 1 of 2 Skip forwards

In the area of Afar in Hadar, Ethiopia, Australopithecus afarensis, or 'southern ape of Afar', now possessed mixed human and chimpanzee characteristics. They had small brains, long, dangly arms, short legs, and a cone-shaped thorax with a large belly. But the structure of their knees and pelvis show that they routinely walked upright on two legs.

Probably descended from Australopithecus anamensis, and just over a metre tall, afarensis foraged for fruit, nuts and seeds in a mixture of savannah and woodland. They may also have obtained animal protein from bird's eggs or termites.

The most famous afarensis remains to have been discovered were those of 'Lucy', found by anthropologist Professor Donald Johanson and his student, Tom Gray, in a maze of ravines at Hadar in northern Ethiopia in 1974, and dated to 3.2 million years ago. The following year Michael Bush, one of Johanson's students, found the remains of more than thirteen afarensis individuals buried together following a natural disaster – possibly a flash flood. The find yielded vital information about afarensis' social organisation, likening it to the social grouping found in chimpanzees.

Professor Robin Crompton of Liverpool University has used computer modelling to reconstruct how Lucy walked based on the proportions of her skeleton. He assumed that Lucy could either have walked upright with a bent hip and knees like a chimp, or with straight legs like a human. Orangutans live between twenty to forty metres above ground in the forests of Indonesia. They spend most of their time in an upright position, but suspend themselves from branches with their long arms. However, orangutans sometimes walk on branches without aid, raising their arms for balance. Orangutans are not as closely related to humans as are chimps. But this behaviour has been observed in wild chimpanzees living in dense forest, suggesting that it could be an ancestral trait which is common to all great apes.

It is thought that the human lineage developed routine bipedalism as a strategy for living on the ground when climate change decimated the forest, leaving wide belts of open terrain with no trees. Crompton believes the forest canopy bipedalism shown by orangutans provided the kick-start for routine bipedalism when our ancestors came down from the trees and began living on the ground. Once our ancestors were forced to adapt to living on the ground, some drew on this behaviour from their existing repertoire as a method of terrestrial locomotion.

Australopithecus afarensis
Based on computer modelling experiments carried out by Professor Robin Crompton of Liverpool University, afarensis is generally regarded to have walked upright, very much like modern man


The challenges of spending more time on the ground would have favoured those hominids whose anatomy and behaviour gave them a reproductive edge over their peers, however slight. Hominids which were good bipedal walkers were clearly at an advantage in this terrestrial environment, because millions of years later, humans still walk on two legs instead of four.

In 2016 it was reported that further footprints made around 3.66 million years ago had been discovered in Tanzania. This was very close to a similar set of tracks which had been discovered in 1976. The impressions were made when a group of afarensis (most probably) walked together across wet volcanic ash, following a volcanic eruption and subsequent rainfall. Experts estimated that the group consisted of a large male (a surprisingly tall 165 centimetres in height adjudged by his footfall), several smaller females, and perhaps a couple of juveniles. The suggested social structure is close to that of modern gorillas.

 

3.5 million

Australopithecus bahrelghazali

Australopithecus bahrelghazali appeared, and flourished until 3.0 million years ago.

The species designation of Australopithecus bahrelghazali is a new one (given in 2012), which has little support at present among most researchers. This is due to the small sample size, its recent designation, and the affinity of the specimen to afarensis material. However, it differs in several important aspects from afarensis (the geography being a major component in and of itself), and therefore may be a new species, or at least a regional variation of afarensis.

The material designated as bahrelghazali was discovered by Michel Brunet's team in the ancient riverbed of Bahr el Ghazal in Chad, 2,500 kilometres west of the Rift Valley. Finds were made in 1995 and 1996. The location in Central Africa was the furthest west that australopithecine material had been found in Africa, unusually well outside of the typical finds zones in east and south Africa.

No further specimens have been found so an impression of bahrelghazali was not immediately possible until a very good approximation could be made in 1999.

 

3.5 million

Australopithecus deyiremeda

Australopithecus deyiremeda was a surprise discovery and announcement, with the latter coming early in 2015. Deyiremeda seems to have flourished between 3.5 and 3.3 million years ago.

Archaeological finds in the Afar region of Ethiopia included jaw bones and teeth, meaning that this 'new' hominin was alive at the same time as several other early human species. The new species was named deyiremeda, meaning 'close relative' in the language spoken by the Afar people.

The bones are thought to have belonged to four individuals, who would have had both ape and human-like features. There are major differences in the detailed anatomy and morphology of the teeth and the upper and lower jaws when compared to other species that were around at the same time. This new species has very robust jaws and smaller teeth. The canine especially is smaller than all known hominins to have been documented in the past. The age of the remains means that this was potentially one of four different species of early humans which were all alive at the same time.

Some researchers dispute whether the various partial remains really constitute different species, particularly for Australopithecus bahrelghazali. But lead researcher, Dr Yohannes Haile-Selassie, curator of physical anthropology at the Cleveland Museum of Natural History in the US, says the early stage of human evolution was probably surprisingly complex. 'Historically, because we didn't have the fossil evidence to show there was hominin diversity during the Middle Pliocene, we thought there was only one lineage, one primitive ancestor - in this case Australopithecus afarensis - giving rise to the next. That hypothesis of linear evolution has to be revisited. And now with the discovery of more species, like this new one... you have another species roaming around. What this means is we have many species that could give rise to later hominins, including our own genus, Homo.'

Australopithecus deyiremeda
Researchers have said that the jaw bones and teeth of this proposed new species, Australopithecus deyiremeda, are different from anything that has previously been found


No further specimens have been found so far, so no impression of deyiremeda can be made.

 

3.5 million

Kenyanthropus platyops

A much shorter-surviving species, Kenyanthropus platyops appeared at the same time as bahrelghazali and deyiremeda, but seems to have died out by 3.3 million years ago (later amended to 3.2 million years).

Discovered by Meave Leakey and her team in 1998 in the west of Lake Turkana in Kenya (near the Ethiopian border), Kenyanthropus platyops was described as an entirely new genus dating back to the middle Pliocene period, positioning itself as a possible direct ancestor of modern humans.

However, the skull found was very distorted, and some researchers believe this may not be a separate species at all. Some refer to it instead as Australopithecus platyops, or even as nothing more than another example of Australopithecus afarensis.

In 2015, it was reported that stone tools unearthed at Lake Turkana in Kenya had been dated to 3.3 million years. If accurate, this makes them the oldest-known stone tools, pre-dating anything created by the Homo genus of humans.

The main suspects for the creation of these tools are either Australopithecus afarensis or Kenyanthropus platyops, meaning that these species may have been more sophisticated than was previously thought. By the end of 2012, a total of 149 tools had been found at the site, named Lomekwi 3, and another field trip in 2014 unearthed more still.

Kenyanthropus platyops
The genus Kenyanthropus was chosen largely to honour Kenya, in which so many vital archaeological discoveries have been made, while platyops derives from Greek, meaning 'flat face'


 

3.2 million

Australopithecus afarensis
Skip backwards Part 2 of 2

Australopithecus afarensis continued to roam a mixed habitat of savannah and woodland beside lakes and floodplains, foraging for fruit, seeds and nuts and maybe even some meat. They probably climbed into trees to avoid sabre-toothed cats such as dinofelis and to sleep in safety at night.

This hominid seems to have lived in social groups of between twenty and thirty. These groups were probably like those of chimpanzees, with dominance hierarchies in which each individual knows their place. Male afarensis probably cooperated to drive away predators. Once mature, females may have joined other troops of afarensis.

But changes were beginning to take place. Climate change would result in many of the species of this period disappearing, replaced in some instances by new species which were better adapted to survival in this new world.

 

Australopithecus africanus

Drying Earth
 

3.0 million

Australopithecus africanus

As Australopithecus afarensis and bahrelghazali disappeared, the first hominid to replace them was Australopithecus africanus, a direct descendant of afarensis, which lasted until 2.4 million years ago.

The world of Lucy and Australopithecus afarensis had vanished. Hidden forces were transforming Earth's climate, with devastating consequences for the African landscape. Temperatures in Africa plummeted and the air became stripped of moisture. By 2.8 million years, humid woodland had shrivelled away, leaving wide belts of open terrain in its place.

The cause of this environmental upheaval was to be found in space. The Earth orbits the sun at a slight tilt, known as the axis of rotation. This means that as our planet spins, it points towards the sun at some times and away from it at others. This is the origin of the seasons on Earth. Three million years ago, this axis was changing so that the Earth pointed away from the sun for longer periods. This caused an overall cooling of the Earth's surface, locking away moisture in ice at the North and South Poles. It also made the climate more seasonal, as the surface dried out.

In Africa, some animals which relied on the forests for their food died out. But others evolved to exploit different dietary sources. For example, many evolved physical adaptations to graze on the new species of plant life called grass which colonised the deforested terrain. Wildlife in Africa diversified as new animal species evolved to exploit different sources of food in a new mosaic of environments.

The same thing seems to have happened to our ancestors, who had previously relied on forest foods such as soft fruit. After three million years, new ape-men were springing up all over the continent, including Australopithecus africanus.

Australopithecus africanus
This is the most complete skull of Australopithecus africanus ever found, with a shorter face than the preceding afarensis species, strong cheekbones to support large chewing muscles, and a brain similar in size to that of modern chimpanzees (Natural History Museum, London)

 

 

2.7 million

Paranthropus aethiopicus

Between about 2.7 and 2.5 million years ago the australopithecines are thought to have split into the genus Homo, which produced modern Homo sapiens, and the genus Paranthropus, which eventually died out.

To complicate the picture, some australopithecines existed for a time alongside both of these and, until recently, many experts classified Paranthropus as australopithecines too.

Paranthropus aethiopicus, one of the earliest examples of this second genus which was not directly related to modern man, appeared in East Africa, and survived until 2.2 million years ago.

It was a short-lived side-shoot of Australopithecus africanus, and existed alongside it. This and subsequent robust species of early human represented very different morphologies than were seen in the known Australopithecus specimens.

Adaptations of the cranium were associated with a 'heavy-chewing complex'. This complex is thought to have made it possible for these early humans to eat large amounts of tough, fibrous foods. Another feature of the robust skull is the presence, at least in males, of a prominent sagittal crest, a bony ridge which runs along the length of the top of the skull. This bony ridge provides an anchoring point for the large temporalis muscles.

These unique adaptations led Robert Broom to place the robust early humans from southern Africa into their own genus, Paranthropus. Several species names have been proposed, including P robustus or P crassidens. In the 1960s palaeoanthropologists began to note similarities between all of the early human species before the appearance of the genus Homo. As such, many researchers began to place all early human species into a single genus (Australopithecus) and described each species as either a 'gracile' or 'robust' Australopith. The robust specimens from southern Africa were then placed in the species Australopithecus robustus.

In recent years, many researchers have sought to emphasise the uniqueness of the heavy-chewing adaptations seen in at least three separate species of early human. Many favour the separation of these species into a robust genus of early human, for which the name Paranthropus was the first used, and therefore has seniority over all other names.

This particular species was eventually superseded by Paranthropus boisei.

 

2.5 million

Australopithecus garhi

The short-lived species Australopithecus garhi appeared around this time, descended either from afarensis or africanus - it isn't clear yet which.

Garhi discoveries were made at Bouri, in the Middle Awash area of Ethiopia's Afar desert (about seventy kilometres south of the Lucy afarensis discovery at Hadar). The area was verdant at this time, with herds of antelope grazing the plains surrounding a lake. Volcanic ash and lava are interbedded with the fossil-bearing strata, providing accurately datable material. The ash just below the fossils erupted at this time.

The research team reported evidence of the earliest traces of animal butchery at the same site. Antelopes had been butchered with the world's earliest known stone tools. There is no direct evidence that garhi used stone tools, but the proximal cut-marked bones provide circumstantial evidence.

Garhi represents one of evolution's many question marks. It was contemporary of africanus but had a smaller brain and retained much of the primitive facial structure of afarensis.

Nevertheless, its mouth was more comparable to modern humans than africanus. Researchers have long assumed that evolution occurs in a linear fashion, with younger species possessing more 'advanced' features than older ones. Garhi complicates this assumption as it seems to be a evolutionary step backwards.

Alternatively, it could be a parallel development from afarensis, a sister species of africanus which has also developed the changes to the mouth but not the larger brain capacity.

The specimens found so far include an associated set of cranial fragments, frontal, parietals, and maxilla with dentition. Garhi's teeth were larger than those of the earlier afarensis. Its braincase, face and palate were more primitive than those of later Homo. The known specimens demonstrate that the thigh bone had elongated a million years before the Homo forearm shortened. The derived human-like humeral/femoral ratio, together with the ape-like upper arm-to-lower arm ratio, provide evidence of the mosaic-like evolution of the features which characterise modern humans.

Garhi was probably the direct ancestor of both Homo rudolfensis and Homo habilis, but vitally, it is not yet certain if Homo rudolfensis was the ancestor of later Homo species, or if Homo habilis was.

 

2.4 million

Homo rudolfensis

Homo rudolfensis ('Rudolf man') first appeared at this time, and flourished until 1.6 million years ago, living in East Africa. By the time of its disappearance, several other species of early human had appeared, including Homo ergaster and Homo erectus, possible descendants of rudolfensis.

Probably descended from Australopithecus garhi, rudolfensis may have lived over a wide area of East Africa, from Ethiopia in the north to Malawi in the south. It was a very tall species, towering above other hominids which were alive at the time - especially the stumpy Homo habilis. Their faces were large and flat in comparison with those of habilis, with flared cheekbones and big molar teeth, and their brains were 56% the size of those of modern man.

Like the slightly later Homo habilis, rudolfensis probably combined foraging with scavenging meat from animal carcasses. This probably placed the two species in direct competition with each other. The large body size of rudolfensis may have made it more effective at scaring away other animals from kills, turning it into a better scavenger.

Both habilis and rudolfensis survived for approximately 300,000 years after the appearance of the species which replaced them (over twice the length of time that Homo sapiens has existed in its modern form). That replacement was long thought to be H ergaster, but a missing link may have existed between the two - Australopithecus sediba.

As for rudolfensis, with only one find dating from 1972, for a long time there was some debate as to its exact classification - and even whether it was really a species fully separate from Homo habilis. Fresh finds in 2012 confirmed that rudolfensis really was a separate species. Along with habilis it is a candidate for a direct ancestor of modern man, but neither species was directly related to the other hominid type which flourished at the time: Paranthropus boisei.

 

 

 

Main Sources

BBC series - Walking with Cavemen, first screened from 1 April 2003

Additional Sources

eLIFE Sciences Publications Ltd

Brunet, M, Beauvilain, A, Coppens, Yves, Heintz, É, Moutaye, A H E and Pilbeam, D - The first australopithecine 2,500 kilometres west of the Rift Valley (Chad). Nature 1995: 378: 273-275.

Leakey, Maeve, Spoor, Fred, Dean, M Christopher, Feibel, Craig S, Antón, Susan C, Kiarie, Christopher, & Leakey, Louise N - New fossils from Koobi Fora in northern Kenya confirm taxonomic diversity in early Homo, Nature 2012: 488: 201-204

 

 

 

     
Images copyright © BBC or affiliates unless otherwise stated. No breach of copyright is intended or inferred. Text copyright © P L Kessler, adapted from numerous sources and notes. An original feature for the History Files.