Studying fossils and extinct animals
Although Sterkfontein is best known for the hundreds of fossils of early hominids discovered here, it has also yielded thousands of animal bones representing a great variety of species, which tell us about the environment and climatic change.
The animals of past ages at Sterkfontein included the now-extinct Dinofelis and Megantereon sabre-tooth cats; the long-legged hyena, Chasmaporthetes; Parapapio, Papio and Cercopithecoides monkeys; a heavy, cow-like animal called a makapania; a tiny, three-toed horse, Hipparion lybicum; a giant hyrax or “dassie”; and a huge chalicothere, a knuckle-walking animal related to a horse.
Palaeontologists have different methods of dating available to them, depending on the environment in which the fossils are found. At the Sterkfontein Caves, one way of determining the age of the fossils is by using radio-isotope dating of the cave deposits. Some isotopes found in these deposits are unstable and decay over time to form “daughter” isotopes at a known rate. By checking the amount of decay of an isotope, geophysicists can work backwards and determine how old the deposit is – and thus the age of the fossil.
Once a few species have been classified and placed in a timeframe, experts can start to examine trends in evolution.
For instance, from fossilised remains of Australopithecus and Homo at Sterkfontein and other sites in East and Southern Africa, we can see how early hominids, having developed bipedalism (the ability to walk permanently on two feet), adapted to life beyond their original forest environment. The study of teeth and facial musculature, together with isotope analysis of bone, provides information on the diet of Australopithecus and Paranthropus hominids.
From animal and plant fossils, we can also determine ancient environments and climatic conditions. Traces of certain plants and small mammals are among the key indicators of climate.
Pliocene to Pleistocene
The environment in the Cradle of Humankind was once far lusher and more tropical than it is today. Just under 2-million years ago, this landscape began to change, opening up into the grassland it is today.
We know of these animals from fossils of their bones preserved in the Cradle of Humankind.
The study of what happens to organisms after they die, are buried and fossilised is known as taphonomy. Analysis of the condition of bones, including signs of breakage and tooth marks, reveals information on how the bones ended up in the caves.
There were four main ways in which the bones of the animals which eventually became fossilised came to be in the caves: through the activities of porcupines, hyenas and big cats, or through falling in.
Palaeontologists look for clues on the bones to uncover their mysteries. Porcupines gnaw bones into sharp points, for example, leaving characteristic chisel marks around the edges. Hyenas have jaws strong enough to crunch bones, breaking them through the middle, so palaeontologists look for tell-tale chips and flakes from the impact of their teeth on a bone. Occasionally, hyenas will also leave toothmarks on a bone.
Large cats such as leopards, on the other hand, don’t have teeth powerful enough to crunch bones, and will leave ragged toothmarks at the end of bones.
One of the most exceptional finds at Sterkfontein, made by University of the Witwatersrand palaeoanthropologist Professor Ron Clarke and his team, was the fossilised skeleton of the australopithecine “Little Foot”, which had probably fallen down a shaft alive between 4-million and 3-million years ago, never to return to the surface.
Studying fossils
Palaeontologists examine the characteristics of a fossil to determine what animal or plant it belonged to and its place in the evolutionary framework.
Three-million years ago, in a geological epoch known as the Pliocene, environmental conditions at Sterkfontein were warmer and wetter than today, and the landscape was a mosaic of forest, woodland and grassland. From fossils, we know the vegetation included liana vines of the kind now found only in tropical forests in Central and West Africa. Fossils of large, forest-dwelling monkeys are also relatively common in the older Member 2 (about 4.2-million to 3.3-million years old) and Member 3 (about 3.3-million to 2.5-million years old) at Sterkfontein, and are evidence of this lusher environment.
Fossils of browsing antelopes such as Hippotragus (similar to a modern-day sable antelope) indicate continuing woodland conditions in Member 4 (about 2.5-million to 2.1-million years old), and after that a marked shift towards open grassland is documented by the fossils of savannah species such as zebras, ostriches and spring hares, as well as many thousands of fossils of grazing antelopes, including wildebeest and hartebeest, that occur in Member 5 (about 1.9-million to 1.5-million years old).
The study of carbon isotopes reflecting diet, and hence environment, confirms this scenario. The data suggest that there was a fairly wooded environment until about 2-million years ago, followed by a marked shift to open environments around 1.8-million years ago, corresponding with the onset of the Pleistocene.
Many human evolutionary changes occurred during the Pleistocene, an epoch characterised by changes in climate, swinging between glacial conditions (colder, drier, with lower sea-levels) and relatively brief interglacial episodes (warmer, wetter, higher sea-levels).
Fossils in Sterkfontein
Fossils are the remains or traces of ancient plants and animals, preserved in rocks such as cemented cave deposits called breccia. Fossils are formed when minerals, including calcium carbonate, envelope or replace bones and other organic matter, hardening or encasing them within rock that remains unchanged for millions of years. The geology of the caves at Sterkfontein has provided an ideal environment for the formation and preservation of fossils.
Some areas of the Cradle of Humankind are so rich in fossils that they have become “time capsules” that provide us with unique relics of specific time periods, and so glimpses into the world in which humanity was born.
A wide cross-section of animal and plant fossils spanning millions of years is preserved at Sterkfontein.
The fossils at Sterkfontein were formed when skeletal remains were covered by soil washed into the caves. Calcium carbonate dissolved in water dripping into the caves suffused through the bones and other organic material, binding them in a matrix of rock and finer sediment called breccia.
At Sterkfontein, there are six Members (sedimentary units or layers) of rock containing fossils dating to between about 4.2-million years and 100,000 years old, giving us an extraordinary history of fauna and hominid development. People who study fossils – palaeontologists and palaeoanthropologists – delve systematically through these rich deposits in search of new information about the past.
The people who study the past
Palaeontologists: Study animal and plant fossils
Palaeoanthropologists: Study prehistoric culture and the anatomy of hominids (human ancestors) and the environment in which they lived
Archaeologists: Study material cultural remains of ancient peoples, such as stone tools
Geologists and geophysicists: Study the Earth and rocks and are involved in dating fossils
Extinct animals
Extinct Parapapio monkey
Two species (Parapapio broomi and Parapapio jonesi) of this extinct genus of large monkey have been found Sterkfontein, dating to between about 3.5-million and 2-million years ago. Parapapios are associated with forest environments and thrived when the local environment was warmer and wetter than today.
They lived at the same time and in the same areas as early baboons of the genus Papio. Other Parapapio species have been found at Taung and Makapansgat, as well as in Angola and East Africa.
Extinct colobus monkey (Cercopithecoides)
There are about 30 species of modern-day colobus monkeys, which live in forest and woodland in tropical Africa and in southern and eastern Asia. They have specialised teeth and complex stomachs for chewing and digesting leaves. The biggest colobus is the large-nosed proboscis monkey, which weighs over 20 kg (44 lb), and lives in Borneo. In the distant past there were many other species of colobus monkeys, including the genus Cercopithecoides, which occurred in Europe and South Africa.
Cercopithecoides monkeys were about twice as large as today’s vervet monkeys. Their fossils have been found in the Cradle of Humankind, at Sterkfontein, Bolts Farm, Kromdraai, Swartkrans, Haasgat and Makapans Valley, covering the period from the late Pliocene to the middle Pleistocene, from about 3-million years ago until 1.5-million years ago. Cercopithecoides also occurred in East Africa. Like modern colobus monkeys and monkeys of other species, Cercopithecoides probably lived in family groups. Because of their large size, they possibly spent time on the ground as well as in trees.
Extinct makapania
This extinct ox-like animal, which lived between 3-million and 2-million years ago, is related to the present-day musk ox of the Arctic and the takin of the woodlands of the Himalayan foothills. All of these belong to a group known as the Ovibovini.
The Makapania broomi type-specimen was found at Makapansgat, another part of the Cradle of Humankind World Heritage Site, about 300 km (185 mi) from Sterkfontein, near Mokopane in Limpopo Province. Makapania fossils have also been discovered at Sterkfontein, Swartkrans, Gladysvale and Motsetse in the Cradle of Humankind.
Extinct hunting hyena (Chasmaporthetes)
These were similar to a modern spotted hyena in size, but had longer legs which possibly made them better hunters. They lived in the Cradle of Humankind between about 3-million and 1-million years ago during the time of Australopithecus and Paranthropus, and Homo, and are known to have existed in East Africa and Eurasia more than 4-million years ago. They spread into America before 3.5-million years ago.
Extinct chalicothere
These strange, knuckle-walking creatures had horse-like heads and steeply sloping backs. Giants at more than two metres (6’5”) tall, chalicotheres ate only soft vegetation such as new shoots. The huge claws on their front feet may have been for pulling down vegetation as they fed, similar to the way gorillas or pandas do today.
Chalicotheres lived between 45-million and about 1.8-million years ago. Their closest living relatives are horses, tapirs and rhinos. Calicothere teeth and limb bones have been found in the Makapans Valley, and a toe bone has been found at Sterkfontein.
Extinct sabre-tooth cat (Dinofelis)
Sabre-toothed cats are so-called because they have long, blade-like, upper canine teeth. While impressive, Dinofelis’ upper canines were not as long as those of Megantereon and Homotherium saber-tooth cats, which lived at the same time in the Cradle of Humankind.
Dinofelis was about the size of a jaguar and had relatively short, but powerful front legs. These big cats are associated with a forested environment and had become extinct by about 1-million years ago.