Human Evolution http://www.becominghuman.org/node/human-lineage-through-time

The earliest fossil hominid, Ardipithecus ramidus, is a recent discovery. It is dated at 4.4 million years ago. The remains are incomplete but enough is available to suggest it was bipedal and about 4 feet tall. Other fossils were found with the ramidus fossil which would suggest that ramidus was a forest dweller. A new skeleton was recently discovered which is about 45% complete. It is now being studied.

A new species, Australopithecus anamensis, was named in 1995 A new species, Australopithecus anamensis, was named in 1995. It was found in Allia Bay in Kenya. Anamensis lived between 4.2 and 3.9 million years ago. Its body showed advanced bipedal features, but the skull closely resembled the ancient apes.

Australopithecus afarensis lived between 3. 9 and 3 Australopithecus afarensis lived between 3.9 and 3.0 million years ago. It retained the apelike face with a sloping forehead, a distinct ridge over the eyes, flat nose and a chinless lower jaw. It had a brain capacity of about 450 cc. It was between 3'6" and 5' tall. It was fully bipedal and the thickness of its bones showed that it was quite strong. Its build (ratio of weight to height) was about the same as the modern human but its head and face were proportionately much larger. This larger head with powerful jaws is a feature of all species prior to Homo sapiens sapiens.

Australopithecus africanus was quite similar to afarensis and lived between three and two million years ago. It was also bipedal, but was slightly larger in body size. Its brain size was also slightly larger, ranging up to 500 cc. The brain was not advanced enough for speech. The molars were a little larger than in afarensis and much larger than modern human. This hominid was a herbivore and ate tough, hard to chew, plants. The shape of the jaw was now like the human.

Australopithecus robustus lived between two and 1. 5 million years ago Australopithecus robustus lived between two and 1.5 million years ago. It had a body similar to that of africanus, but a larger and more massive skull and teeth. Its huge face was flat and with no forehead. It had large brow ridges and a sagittal crest. Brain size was up to 525cc with no indication of speech capability. they had huge, broad megadont cheek teeth with thick enamel and focused their chewing in the back of the jaw. Large zygomatic arches  allowed the passage of large chewing muscles to the jaw and gaveP. robustus individuals their characteristically wide, dish-shaped face. A large sagittal crestprovided a large area to anchor these chewing muscles to the skull. These adaptations provided P. robustus with the ability of grinding down tough, fibrous foods. It is now known that ‘robust’ refers solely to tooth and face size, not to the body size of P. robustus.

Australopithecus boisei lived between 2. 1 and 1. 1 million years ago Australopithecus boisei lived between 2.1 and 1.1 million years ago. It was quite similar to robustus, but with an even more massive face. It had huge molars, the larger measuring 0.9 inches across. The brain size was about the same as robustus. Some authorities believe that robustus and boisei are variants of the same species.

Homo habilis was called the handy man because tools were found with his fossil remains. This species existed between 2.4 and 1.5 million years ago. The brain size in earlier fossil specimens was about 500cc but rose to 800cc toward the end of the species life period. The species brain shape shows evidence that some speech had developed. Habilis was about 5' tall and weighed about 100 pounds. Some scientists believe that habilis is not a separate species and should be carried either as a later Australopithecine or an early Homo erectus. It is possible that early examples are in one species group and later examples in the other.

Homo erectus lived between 1. 8 million and 300,000 years ago Homo erectus lived between 1.8 million and 300,000 years ago. It was a successful species for a million and a half years. Early examples had a 900cc brain size on the average. The brain grew steadily during its reign. Toward the end its brain was almost the same size as modern man, at about 1200cc. The species definitely had speech. Erectus developed tools, weapons and fire and learned to cook his food. Only his head and face differed from modern man. Like habilis, the face had massive jaws with huge molars, no chin, thick brow ridges, and a long low skull. Though proportioned the same, he was sturdier in build and much stronger than the modern human.

He traveled out of Africa into China and Southeast Asia and developed clothing for northern climates. He turned to hunting for his food. The picture below shows a trio of Homo species which first appeared about 2 mya. It argues against the idea of linear progression towards modern day humans, instead, illustrating cladogenesis.

NatGeo article Homo sapiens (archaic) provides the bridge between erectus and Homo sapiens sapiens during the period 200,000 to 500,000 years ago. Many skulls have been found with features intermediate between the two. Brain averaged about 1200cc and speech was indicated. Skulls are more rounded and with smaller features. Molars and brow ridges are smaller. The skeleton shows a stronger build than modern human but was well proportioned.