Evolution of Australopithecines to Homo habilis

The study of the evolution of the human species has been characterized by astounding discoveries, immense public interest and a copious amount of controversy. From the earliest parts of the 20th century, new fossil hominid finds have disrupted the widely held views on the evolution of our species.

Considering the evolution of humans we can say the modern people are Homo sapiens .However, we are not the only species of humans who have ever lived.  There were earlier species of our genus that are now extinct.  In the past, it was incorrectly assumed that human evolution was a relatively straightforward sequence of one species evolving into another.  We now understand that there were times when several species of humans and even other hominins were alive.  This complex pattern of evolution emerging from the fossil record has been aptly described as a luxuriantly branching bush on which all but one twig has died off.  Modern humans are that last living twig.  Complicating this evolutionary history even more is the realization that our ancestors very likely mated successfully with members of other closely related species from time to time.  As a consequence, our inherited gene pool was enriched by added genetic diversity.  This sort of genetic mixing has recently been documented for Neandertals and early modern Homo sapiens living 40-60,000 years ago.  It is also likely that there were genetic bottle necking events that periodically reduced our diversity.  That largely accounts for the fact that despite our huge human population today, we are remarkably similar genetically compared to other primate species.  It also explains why we are now the only surviving hominin species.  

However the studies of evolution directed towards the  morphology, taxonomy and evolution of one particular group of hominids, the australopithecines. This diverse group of hominids first appeared in Africa sometime around 4.2 Mya (millions years ago) and diversified into a number of forms before the last recorded member of the group went extinct around 1.4 Mya. A number of species have been recovered since 1925, and will be considered here: Australopithecus anamensis, A. afarensis, A. africanus, A. garhi, Paranthropus aethiopicus, P. boisei and P. robustus. 

human family tree

Australopithecus anamensis

age: 4.2 – 3.9 mya
brain size: unknown
fossils found: tibia, lower jawbone
adaptations: very likely bipedal, thick enamel on teeth (hominid characteristic)
location found: Kenya, Africa
notes: tibia shape indicates bipedalism

Australopithecus aferensis

age: 3.9 – 2.9 mya
brain size: 375 – 500 cc (large male–female size difference)
fossils found: hundreds of fossils, fourteen partial skeletons, and footprints(!)
adaptations: certainly bipedal, chimp-like skull, flat nose, no chin w/ human-like teeth, jaw between ape & human
location found: Ethiopia, Tanzania, Cameroon
notes: This is Lucy's species; she's an original, important "missing link."

Australopithecus africanus

age: 3 – 2 mya
brain size: 420 – 500 cc
fossils found: partial skull, cranium, body & pelvis
adaptations: fully human-shaped jaw, canine teeth reduced from afarensis, human-like pelvis
location found: South Africa
notes: everything seems clearly adapted from afarensis

Australopithecus garhi

age: 2.5 mya
fossils found: partial skull
location found: Ethiopia
notes: some evidence for tool use, otherwise not much known

Australopithecus aethiopicus

age: 2.6 – 2.3 mya
brain size: 410 cc
fossils found: "The Black Skull" and some minor fossils
adaptations: baffling; small brain, massive face & very strong jaw
location found:Ethiopia, Kenya
notes: some say this is perfect intermediate between afarensis and boisei, limited information

Australopithecus robustus

age: 2 – 1.5 mya
brain size: 530 cc
fossils found: many, mostly cranial and dental
adaptations: body like africanus, but larger skull, molars, and massive face & brow ridge, small canines
location found: South Africa
notes: bones found w/ robustus fossils may have been tools, this line of hominids had strong jaws and huge molars for crunching rough food, then probably went extinct (no descendants in southern Africa)


Australopithecus sediba

age: 1.95 – 1.8 mya
brain size: 420 cc
fossils found: two partial skeletons, most of cranium in juvenile
adaptations: more Homo adaptations than any other Australopithecine, pelvis is particularly advanced for bipedality so that it may have been capable of running, and brain case is shaped more towards human
location found: South Africa
notes: New discovery, described in April, 2010 ; pelvis and leg indicate it's bipedal; more recent than many Homo fossils, thus unlikely to be human ancestor; probable adult height 4'6" for male, 4'2" for female

Australopithecus boisei

age: 2.1 – 1.1 mya
brain size: 530 cc
fossils found: many, mostly cranial and dental
adaptations: may just be robustus
location found: Tanzania, Kenya, & Ethiopia, Africa
notes: used to be Zinjanthropus; an unlikely human ancestor, probably went extinct due to over-specialization with it's huge molars and small canines; some make them Paranthropus boisei

Homo gautengensis

age: 2 million to 600,000 years ago
brain size: awaiting publication
fossils found: partial skull, several jaws, teeth and other bones
adaptations: bipedalism, further information awaiting publication
location found: Sterkfontein Caves, South Africa
notes: Very stocky! 3 foot tall and 110 pounds; bipedal tree dweller

Homo habilis

age: 2.4 – 1.5 mya
brain size: 500 – 800 cc
fossils found: many
adaptations: primitive face, smaller teeth than australopithecines, human-shaped brain, had "Broca's area," a section of brain we currently use for speech
location found: Kenya & Tanzania, Africa
notes: named habilis for tools found with fossils, may need to be more than one species, Homo rudolfensis is suggested in addition


 References :

http://www.ecotao.com/holism/hu_austral.htm

www.gnolls.org/.../the-paleo-diet-for-australopithecines-approaching..

http://humanorigins.si.edu/evidence/human-family-tree

http://humanorigins.si.edu/evidence/human-fossils/species

http://www.columbia.edu/itc/anthropology/v1007/2002projects/web/australopithecus/austro.html