Australopithecus africanus

Australopithecus africanus is an extinct species of early human relative that lived between about 3.3 and 2.1 million years ago in South Africa. The first fossil of this species, known as the Taung child, was discovered and described by scientist Raymond Dart in 1924. This finding was important because it showed that humans might have evolved in Africa, which was a new idea at the time.

Australopithecus africanus had a small brain, about the size of an orange, and teeth that were good for chewing tough foods. These early humans could walk on two legs but also had some body features that suggest they still spent time in trees. They ate a mix of foods, including grasses, seeds, and harder items like nuts, especially when other food was scarce.

Scientists are still learning about how A. africanus fits with other early human relatives. Some think they might be ancestors of the genus Homo, which includes modern humans, while others have different ideas. This species lived in areas that had both forests and open grasslands. Sadly, many of their fossils were found in caves, likely because they were sometimes eaten by large animals like big cats or birds of prey. Climate changes and competition with other early humans may have led to their disappearance.

Research history

Discovery

In 1924, a scientist named Professor Raymond Dart found a very old skull of a young child in South Africa. This skull, called the Taung child, was special because it showed features that were a mix between apes and humans. It had a small brain but walked on two legs, which was a big clue about how humans might have evolved.

Classification

When the Taung child was found, scientists did not know where to place it. It did not fit neatly into groups for either humans or apes. Over time, more fossils were discovered, and scientists began to see that this ancient creature, named Australopithecus africanus, was an important part of human history. It helped prove that humans evolved in Africa, as Charles Darwin had suggested many years earlier.

Anatomy

Based on 4 specimens, the A. africanus brain volume averaged about 420–510 cc. The inner ear had wide semicircular canals like non-human apes and loose turns at the end of the cochlea like humans. A. africanus had a jaw that jutted out, a somewhat dished face, and a defined brow ridge. The teeth were large with thick enamel, and the canines were reduced in size compared to non-human apes.

In terms of build, A. africanus had an average weight of around 30.7 kg and an average height of about 124.4 cm. The spine and neck bones showed a mix of ape-like and human-like features, suggesting they could move both in trees and while walking upright. The arms were relatively long compared to the legs, but not as long as in non-human apes. The hand and arm showed a mix of human and ape features, with curved fingers and a precision grip useful for tool making. The leg bones clearly show that A. africanus walked on two legs, though some aspects were more similar to apes. The foot was mostly humanlike, with a stiff midfoot and an adducted big toe.

Palaeobiology

Diet

Scientists have studied what A. africanus might have eaten. In the past, they thought A. africanus ate many different foods, while another ancient human relative, P. robustus, mostly ate tough plants. More recent studies using special tests on the teeth show that A. africanus ate a mix of foods, including plants from dry areas like grasses and seeds, as well as some insects like locusts or termites. They might have also eaten small animals, but not many.

The teeth of A. africanus look like they could crush hard foods like seeds and nuts, but it seems they did not eat these very often. Sometimes, when food was scarce, they may have used stones to crack open nuts. We also know that A. africanus did not often eat foods that cause cavities, like sugary fruits or honey. One tooth showed signs that this individual ate acidic foods, maybe citrus fruits.

Society

It is hard to know how A. africanus lived together in groups. One study of their teeth suggests that females might have moved away from where they were born, while males stayed closer to home. This is similar to how some modern humans live, where females move to new groups while males stay. The teeth of males were not very big compared to females, which might mean males did not fight much.

Pathology

Some A. africanus fossils show signs of health problems. For example, one young fossil had severe gum disease, which would have made chewing very hard. Another fossil showed signs of eating too many acidic foods, which can damage teeth. There was also a fossil that might have had a healed ankle injury, perhaps from falling from a tree, but this is not certain.

Palaeoecology

Australopithecus africanus lived in areas with many different kinds of environments. At a place called Sterkfontein, scientists found old wood from a type of tree that only grows in very wet, dense forests today. This suggests that long ago, the area might have had more rain and closer forests. The animal fossils found there show a mix of places like open grasslands and woodlands.

Scientists think that these early humans liked cooler places and usually lived above 1,000 meters in elevation, where temperatures were comfortable during the day but cooler at night. Some scientists believe that big animals, like cats, might have brought australopithecine bones into caves. It's also possible that birds of prey attacked some of these early humans.