Human evolution


Pliocene hominids

After Ramapithecus no fossils are available for almost 10 million years, which is a big gap in phylogeny of man.

Oreopithecus fossils were discovered from lignite mines in Italy. One nearly complete skeleton of the abominable Coal Man was unearthed from Italy and later about 200 fossils were collected from Europe and East Africa. Dentition was human, canines were small and face short but premolars and molars were ape-like. Pelvic girdle was broad, indicating erect posture. It was an herbivore living in swampy areas.

Australopithecus africanus,the southern ape” is the most primitive of Australopithecines that existed between 5.5 and 2 million years ago. Fossil of a 5-year old boy (Taung baby) was discovered from South Africa by Prof. Raymond A. Dart in 1924.

It was 5 feet tall and walked erect. Vertebral column had a lumbar curve and pelvis was broad. Foramen magnum was placed under the skull. Teeth human and dental arch smoothly rounded. Palate seems to be shallow anteriorly and deep posteriorly.

Canines were small and simian gap absent. Premolars and molars greatly enlarged relative to incisors and canines. Cranial capacity was 450-700 cc. Face was prognathous with long palate but less prominent eyebrow ridges and without chin. Orbits were large and rounded. Nasal bones were flat, giving the short face a dish-shaped appearance.

Australopithecus occurred in two forms: a small gracile and a larger robust form spread in Tanzania, Kenya and Ethiopia and South Africa. Many scientists are now using the generic name Paranthropus, which was originally given to the species robustus, to refer to the robust forms of Australopithecus, which includes robustus, boisei and aethiopicus.

Australopithecus afarensis was a gracile form and probably a descendant of A. africanus. One almost complete skeleton of a female named “Lucy” was discovered from Afar (Ethiopia) by Donald Johanson in 1973. It was dated at 3.5 million years. It was about 5 feet tall and walked erect and had an arched foot to support the bipedal gait. Cranial capacity was 400-500 cc. Canines were small with thick layer of enamel and molars were designed to grind tough material.

Australopithecus garhi. A fragmentary skull was excavated in 1997 by Asfaw and White from Bouri village in the middle Awash region in Ethiopia and dated at 2.5 million years. The fossil was found near antelope bones which were butchered by it using specialized stone tools that were carried with it from other places where the raw material for it was available. The stone hammers, axes and blades enabled this species to exploit a broader range of habitats and prey to obtain energy rich food that was necessary for the enlargement of energy consuming brain.

Australopithecus anamensis fossils, discovered near Anam lake at Kanapoi and Allia Bay in Kenya by Meave G. Leakey, were dated to about 4 million years. Skull fragments and teeth were similar to those of earlier species but arms and leg bones were more advanced and indicative of bipedal gait.

Ardipithecus ramidus is represented by 21 specimens found near Lake Turkana and from Aramis in the Awash Valley in 1995. Dated back to 4.4 million years, it perhaps walked erect. It is believed to be a sister species of anamensis. 

The following three species were robust forms of Australopithecus, sometimes identified by the separate generic name, Paranthropus, as they seem to have descended from a common ancestor.

Australopithecus robustus (=Paranthropus robustus) was first discovered by Robert Broom in 1939 from South Africa and dated to 1.5-2.0 million years. It is characterized by heavily built skull having rounded appearance, higher vertex and a bony keel on the top for the attachment of large jaw muscles. Forehead was slanting and eyebrow ridges massive. Foramen magnum and occipital condyles were anteriorly placed. Dental arch was rounded and massive without diastema and simian shelf. Incisors and canines were small and spatulate, while premolars and molars were very large.

Zinjanthropus boisei, the “Nutcracker Man” was discovered by L.S.B.Leakey in 1959 from Tanganyika in East Africa and at Olduvai gorge in Tanzania, along with stone tools, and was dated to about 1.7 million years. It had massive jaws and teeth, with small incisors and large canines. There is cerebral enlargement with a cranial capacity of 600 cc. Face was protruding and forehead high, having prominent eyebrow ridges. Nasal spine was elevated.

Australopithecus aethiopicus was discovered by Allan C.Walker from Lake Turkana in Kenya and is represented by a 2.5 million years old blackish skull. It is related to A. robustus and boisei and may be their ancestor.

Pleistocene hominids

Homo habilis, called the “Able Man” lived 1.85-2.6 million years ago and walked erect. Fossils were discovered by Louis Leakey in 1959 from Olduvai Gorge in Tanzania, where later several teeth, jaw and skull fragments were discovered. Its premolars and molars were smaller and anterior teeth larger. It was 140 cm tall, with cranial capacity of 700 cc and human teeth. It was a habitual biped and probably ancestral to all Homo.  It hunted small animals and was a scavenger of large carcasses. Face was less prognathous and nasal bones convex.  It was closely related to A. africanus but was more advanced in features and occupied similar ecological niche.

Homo erectus fossil remains dating from 1.9 million years to about 250,000 years discovered from Java, China and later Europe and Africa are collectively known as Homo erectus, the archaic man that had larger brain and used stone hand axes. Supraorbital ridges are prominent, with an indented area behind them.

It had massive face that projected below and heavily built mandibles, without a chin that were moved by strong masseter muscles. Teeth are similar to ours but incisors are slightly larger and shovel-shaped having enlarged pulp cavity, an adaptation for hard chewing. They knew the controlled use of fire to cook food and keep them warm. The use of fire was perhaps necessary to occupy caves that were inhabited by large carnivores. The mean cranial capacity was 1020 cc, which was approximately twice the size of australopithecines but only three-fourth of Homo sapiens.

Homo ergaster, considered the African counterpart of Homo erectus, was discovered from Koobi Fora in Kenya and dated to 1.6 million years. In 1954 hominid remains from Algeria and Morocco showed affinities with the Chinese form of Homo erectus. After 1970, Richard Leakey unearthed fossils from the eastern shores of Lake Turkana and one complete skull from Koobi Fora that is believed to be the earliest Homo erectus fossil in Africa. 

Pithecanthropus erectus (Java Man) was discovered by a Dutch army officer, Eugene Dubois in 1891. Skull cap, few teeth and a femur are known. Forehead was low and supraorbital ridge. Cranial capacity was 775-900 cc. Height was about 5 feet and it walked erect efficiently. Bones of the skull were extraordinarily thick. Face was prognathous, chinless and skull flat on the top and projected behind.

Sinanthropus pekinensis (Peking Man) was first reported by a Canadian Professor, Davidson Black in 1927, who found only one skull. It was similar to Java man but skulls were small and cranial capacity 850-1200 cc. Eyebrow ridges were stout. Stone tools of varied designs were also found along with bones of large animals and pieces of charred wood and bones. It walked erect.

Homo heidelbergensis is represented by a single jaw recovered from a sandpit near Heidelberg in Germany in 1907. Lower jaw was massive and chinless but teeth were stout and human. The anatomical features were more advanced than those of the African and Asian forms of Homo erectus. They were low-browed hominids having thick bones and robust skeletons and perhaps represented earlier stage of Homo sapiens.

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