Nairobi’s Oldest Residents EarthCache

The Great Rift Valley in Kenya has been associated with Prof Leakey and pre historic man. Here at the Nairobi Museum, a number of these fossils are on display and there is background to the finds across Kenya. Most especially in the African Rift Valley.

Discovery of Early Hominins

The immediate ancestors of humans were members of the genus Australopithecus . The australopithecines or australopiths) were intermediate between apes and people. However, both australopithecines and humans are biologically similar enough to be classified as members of the same biological tribe--the Hominini . All people, past and present, along with the australopithecines are hominins . We share in common not only the fact that we evolved from the same ape ancestors in Africa but that both genera are habitually bipedal , or two-footed, upright walkers. By comparison, chimpanzees, bonobos, and gorillas are primarily quadrupedal , or four-footed.

Where the fossils fit in the geological record

Over the last decade, there have been a number of important fossil discoveries in Africa of what may be very early transitional hominins, or proto-hominins. These creatures lived about the time with chimpanzees and bonobos, during the late Miocene and early Pliocene Epochs. The fossils have been tentatively classified as members of three distinct genera--Sahelanthropus , Orrorin , and Ardipithecus . Sahelanthropus was the earliest, dating 7-6 million years ago. Orrorin lived about 6 million years ago, while Ardipithecus remains have been dated to 5.8-4.4 million years ago. At present, the vote is still out as to whether any of these three primates were in fact true hominin.
The earliest australopithecines very likely did not evolve until 5 million years ago or shortly thereafter (during the beginning of the Pliocene Epoch) in East Africa. The primate fossil record for this crucial early transitional period leading to australopithecines is scanty and somewhat confusing at present. However, by about 4.2 million years ago, unquestionable australopithecines were present. By 3 million years ago, they were common in both East and South Africa. Some have been found dating to this period in North Central Africa also. As the australopithecines were present, African forests were progressively shrinking and grasslands, or savannas , were advancing. In this sort of environment, bipedalism would very likely have been an advantage.
By 2.5 million years ago, there were at least 2 lines of hominins descended from the early australopithecines. One line apparently was adapted primarily to lake margin grassland environments and had an omnivorous diet that increasingly included meat. Among them were our early human ancestors who started to make stone tools by this time. The other line seems to have lived more in mixed grassland and woodland environments, like the earlier australopithecines, and was primarily vegetarian. This second, more conservative line of early hominins died out by 1 million years ago or shortly before then. It is likely that all of the early hominins, including humans, supplemented their diets with protein and fat rich termites and ants just as some chimpanzees do today.

Where the major hominid fossils have been found in Africa

History of Discovery

In 1924, Raymond Dart, an Australian anatomy professor at the University of Witerwatersrand in Johannesburg, South Africa, obtained a fossil skull that had been blasted out of a nearby limestone quarry at Taung . Because of its small size, he called it the "Taung baby."

The oldest fossil hominins have been recovered from sites in East Africa, especially in the Great Rift Valley. One of the most important sites there is Olduvai Gorge . It is an approximately 48 km long, eroded canyon complex cutting into the Serengeti Plain in Northern Tanzania. It is only about 90 m deep, but its neatly stratified layers of dirt and rock interspersed with easily datable volcanic ash and lava layers cover the last 2.1 million. The remains of many australopithecines and early humans have been found at Olduvai. When these ancient hominins lived there, it was a grassland that probably had abundant food sources.

Louis and Mary Leakey

Early hominin fossils from Olduvai Gorge are known mostly as a result of the many expeditions of Louis and Mary Leakey . Louis began searching there in 1931, and his second wife Mary joined him in 1935. However, it was not until 1959 that they found their first early hominin fossil.

In northern Kenya and southern Ethiopia, there is an arid region around Lake Turkana in the Great Rift Valley that has exposed geological deposits dating to at least 4.3 million years ago. Richard Leakey, the son of Mary and Louis Leakey, began looking for hominin fossils there in the late 1960's. During the 1970's, his team of field researchers from the National Museum of Kenya made a number of important finds, including fossils of early humans who will be described in the next tutorial of this series.
While working on the western side of Lake Turkana in 1985, an American paleoanthropologist named Alan Walker made an important discovery. This was a nearly complete robust australopithecine skull with an unusually large sagittal crest and some features reminiscent of the more ancient Australopithecus anamensis. Manganese in the soil deposit where it was located stained it black. As a result, this unusual fossil has become known as the "black skull." It has been classified as Australopithecus aethiopicus (named after Ethiopia). Since it dates to 2.5 million years ago, it is a prime candidate for being the earliest robust australopithecine species.

The Black Skull (which you can see inside)

In 1995, Meave Leakey, the wife of Richard Leakey, began discovering bones of a very early australopithecine species at several sites southwest of Lake Turkana. She named it Australopithecus anamensis ("anam" is "lake" in the Turkana language).

(Ack: Palomar College - Department of Anthropology)

In order to substantiate your visit and be able to claim this Earthcache, a number of questions need to be answered and submitted to the cache owner, via e-mail.

You should (if possible) also post a photograph on the site with your log of you or your team and GPSr standing near GZ with the glass enclosure or other identifiable feature nearby.

1. Describe what you see behind the glass at GZ (outside museum - no fee needed) and why it is of interest geologically? Describe the fossil and what identifies it as not being of a modern day species./p>

The glass structure at GZ

2. Looking at the fossil in the room - describe the difference between the fossil you see and naormal (fresher) piece of bone from a similar animal? Explain how a fossil may be formed.

3. Describe how a fossil may be dated.

4. If you managed to get through the museum, describe some of the fossils and other interesting facts that you picked up there (It is not necessary to enter the museum to claim this EC). Photos in your log are also welcome.

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