Miocene Epoch

23 to 5.3 million years ago

15 MILLION YEARS AGO

Freshwater dolphins once lived in central Australia where a huge inland sea had existed. It is also claimed that Australia began to experience drier conditions from this moment on. Perhaps the Blue Mountains were weathering down to size and no longer producing the intense rainfalls considered necessary over the Western side of the mountain range to replenish the inland sea?

Earth in the Miocene period around 14 million years ago. Image © 1997 Christopher R. Scotese. As of 2014, an updated map can be downloaded from the Colorado Plateau Geosystems, Inc. web site and created by Professor Ronald C. Blakey of Northern Arizona University (NAU).

13 to 10 MILLION YEARS AGO

Temperatures dropped substantially across the globe. Large glaciers appeared on the Antarctic continent, arctic North America, and other areas. Whether this cold period is the result of (i) renewed mountain building; (ii) sudden plant growth throughout the world; (iii) a reduction in energy output from the Sun; or (iv) the possibility that the Earth is wobbling along its orbit after an asteroid had impacted with it (or a massive volcano had erupted), scientists can only speculate at this time.

The great whale predators were among the 20 per cent of animals to become extinct at the time the first glaciers appeared on Antarctica.

10 to 5 MILLION YEARS AGO

Nearly 10 million years ago, most of Africa was covered by a giant forest, especially near the equator and going down south a fair way. The forest soon gave way to fewer trees and more open plains towards the far north until it met up with the more desert-like expanses of the Sahara due to mountain building in the Himalayas.

Despite these great forests, Africa was starting to experience slightly less rainfall than usual leading to the creation of vast savanna-like areas with fewer trees. Now our earliest ancestors (possibly one among a number of other primates) started coming down from the trees and learned to adapt to the harsher, more open savanna landscape.

During this time, one species of primate appeared known as Ramapithecus. This primate is considered by some authorities to be one of the earliest hominids as indicated by the structure of its teeth and jaws. Of course, whether this hominid is our earliest ancestor is debatable (could there have been other similar groups of hominids evolving at this time, and in other parts of the world?).

The evidence for saying this creature is probably one of the earliest hominids can be seen from their teeth and jaw structure. Early forms of the creature suggest they lived largely in the tropical forests because of their large projecting canine teeth which was used to tear soft plant material. But later forms of Ramapithecus, although still ape-like, had canines that did not project beyond the other teeth, and so the whole set of teeth seem to be designed more for grinding tougher, more fibrous foods found commonly in the open and drier grasslands of the savannas.

Whether Ramapithecus is really our earliest hominid ancestor or just another adventurous group exploring the savanna country, we can only wait and see as the evidence emerges from the fossil records.

UPDATE
2002

Scientists have found the remains of a 7-million-year-old skull named "Toumai" in the central African country of Chad. What has excited the scientists with this find is in the shape of the teeth and jaw — it looks remarkably human. Yet the rest of the skull looked nothing more than those of an oversized chimpanzee. This is the oldest skull to have this human/chimpanzee combination feature and some scientists are claiming it could be a direct link to our earliest known ancestors.

UPDATE
April 2005

Scientists have officially confirmed with the help of computer reconstruction of the skull and jaw that the creature named "Toumai" is indeed more human than ape. This means the skull could be our oldest known ancestor. And it is possible this creature may have walked upright.

UPDATE
September 2004

A French-led team of scientists has studied part of the left thighbone of a chimp-sized human-like hominid that lived in Kenya on the great African continent over 6 million years ago. Dubbed the Millenium Ancestor (or the more scientifically-correct term of Orrotin tugenensis), this hominid has been found to have the ability to walk upright on two legs for a substantial part of its life. This pushes back the record for the oldest known upright-walking hominid (once held by a well-preserved female hominid named Lucy) by nearly 3 million years.

Originally found by French scientists in 2000, the bones were independently analysed by American scientists to help determine the age of the bones and whether the creature could have walked upright by measuring the bone thickness in the upper and lower portion of the thigh bone. Now the results are in and the facts are truly amazing.

The thickness of the bone in the part that meets the ball in the thigh was said to be thinner than the bone meeting the knee joint by a ratio of 1 to 3 according to CAT scans. For modern humans, the ratio is at least 1 to 4. For modern chimpanzees and gorillas that still rely on walking mostly on four legs, the ratio is approximately equal.

The conclusion is virtually undeniable: this 6 million year old hominid could and probably did walk upright for much of its life.

As Dr Robert Eckhardt of Pennsylvannia State University which led the CAT scan team said:

"In present-day chimps and gorillas, the thickness in the upper and lower parts of that bone are approximately equal.

'In modern humans the bone on top is thinner than on the bottom by a ratio of one to four or more. The ratio in this fossil is one to three. We have solid evidence of the earliest upright posture and bipedalism securely dated to 6 million years." (1)

NOTE: With so many prehistoric skulls of the hominid variety uncovered in Africa, the continent has been described as the cradle of mankind. But whether Africa is really the origin of mankind was debatable until recent advances in DNA analysis of all the human species alive today has identified the group of humans whose DNA is considered the oldest (i.e. those living in Africa).