In this scheme, only two families are recognised with all the Great Apes including humans placed into the same family, the Hominidae or hominids. The next branching of this evolutionary tree divides the orang-utans into one subfamily and all the remaining Great Apes into another subfamily. Then at the tribe level, gorillas, chimpanzees and humans separate onto different branches of the evolutionary tree with humans in the Hominini or hominin branch.
As a result of this classification change, modern humans and all our extinct ancestors on our own branch of the evolutionary tree are now known as hominins rather than as hominids as they were formerly known in old classifications.
It refers to a taxonomic group that occurs in the classification hierarchy between subfamily and genus. As our ancestors evolved, their jaws and teeth changed in many ways. Some tooth changes were apparent five million years ago and additional changes have occurred since then. Read more - Shorter jaws with smaller teeth. Comparison between the legs of a modern human, Australopithecus afarensis and a modern chimpanzee, showing the differences in upright walking abilities.
By five million years ago, our ancestors had developed the ability to walk on two legs but their gait was quite different from our own and their skeletons retained some features that helped them climb trees. Read more - Walking on two legs. The Australian Museum respects and acknowledges the Gadigal people as the First Peoples and Traditional Custodians of the land and waterways on which the Museum stands.
Image credit: gadigal yilimung shield made by Uncle Charles Chicka Madden. This website uses cookies to ensure you get the best experience on our website. Learn more. From the side view, early hominin faces were concave or dish-shaped and projecting forward at the bottom due to their relatively small brain cases and huge teeth and jaws.
In contrast, our teeth and jaws are relatively small, and our faces are nearly vertical. NOTE: When the lower portion of the face markedly projects forward as in the case of the early hominins , it is known as prognathism.
Australopithecine and other early hominin fossils have been found only in Africa. The majority of them were discovered in East and South Africa. However, some also were found in Chad, which is located in North Central Africa. Current evidence indicates that there were as many as 12 species of early hominins between 6 and 1. The following species are the most widely accepted ones:.
The fossil record of early hominins is being added to by new important discoveries almost every year. As a result, it is not yet clear how many species of them actually existed nor is it certain what their evolutionary relationship was to each other.
However, the broad outlines of this complex evolutionary history are already known and are summarized here. To see a more complete listing of proposed species of early hominins and their immediate ancestors, select the button below. It would be helpful to have a printout of this table in order to understand the discussion of the early hominins that follows.
Australopithecine Species. Australopithecus anamensis may have been the earliest australopithecine species. They lived about 4. Unfortunately, little is known about them due to the scarcity of their fossils and the fact that the ones that have been found are highly fragmentary. This species apparently was descended from Ardipithecus ramidus , which lived around 4.
Anamensis was bipedal but may still have been an efficient tree climber. The shapes of the arm and leg bones indicate that it was bipedal. The canine teeth are relatively large compared to later australopithecines and humans. The alignment of teeth in the jaw is somewhat rectangular, reminiscent of apes, rather than like the modern human parabolic dental arch like the McDonald's golden arches sign.
Anamensis remains have been found in what had been woodlands around lakes. Their diets were apparently mainly vegetarian with an emphasis on fruits and nuts. Australopithecus afarensis lived about 3. Skeletally, they were still somewhat transitional from earlier ape species. This can be seen in their legs which were relatively shorter than those of the later australopithecines and humans. Afarensis also had slender curved fingers reminiscent of chimpanzees.
Because of these anatomical characteristics, it has been suggested that they were less efficient bipeds and more efficient tree climbers than the later australopithecines.
Afarensis canine teeth were relatively large and pointed, reminiscent of apes. They projected somewhat beyond their other teeth but not as much as in chimpanzees. Some of the male afarensis had small sagittal crests. Australopithecus afarensis Lucy Australopithecus afarensis reconstructed appearance Kenyanthropus platyops reconstructed appearance Tim White and some other paleoanthropologists believe that there was considerable physical variation within the species Australopithecus afarensis.
They suggest that the recently discovered fossils classified as Kenyanthropus platyops 3. White discounts the flattened face of platyops as being due to the deformation of the bones by ground pressure after death. Its discoverer, Meave Leakey, disagrees. She believes that platyops was a separate species and that it was more likely to have been the progenitor of humans.
Additional hominin fossils from the crucial time period of million years ago must be discovered to conclusively determine the place of platyops in our evolution. Australopithecus africanus lived about 3.
Skeletally, they were less ape-like than earlier species of australopithecines but were still usually small and light in frame like afarensis. However, the teeth of africanus were in some ways more like humans than like afarensis. Specifically, the front teeth of africanus were relatively large like ours and their canine teeth did not project beyond the others.
Microscopic wear patterns on africanus teeth suggest a diet consisting of relatively soft foods, which very likely included some meat along with plants. This does not necessarily imply efficient hunting skills. More likely, they obtained meat by scavenging what remained on the abandoned corpses of large animals killed by lions and other predators. It is possible that they also did some hunting of small animals in much the same inefficient manner of chimpanzees today.
They probably ate insects and eggs as well. The classification of Australopithecus garhi is still very problematical. This Ethiopian fossil has been dated to 2.
Largely for that reason, some paleoanthropologists have suggested that garhi is a variant of africanus. However, several features of the head of garhi look more like a holdover from the older afarensis species. On the other hand, the relative lengths of the arms and legs of garhi are more reminiscent of the first humans. The discovery of butchered animal bones with garhi suggests that their diet included at least some meat, as was the case with africanus. Paranthropoid Species.
T he australopithecines have been referred to collectively as gracile species literally "gracefully slender" of early hominins. Most of them were relatively small, slender, and delicate boned compared to the somewhat more muscular, robust species paranthropoids that mostly came later. However, this is not always a reliable descriptive distinction because the range of variation in physical appearance of the two groups of species overlaps. Subsequently, some individual graciles were bigger than some of the robust ones.
However, the robust species shared some characteristics of their heads that dramatically show that they had diverged from the evolutionary line that would become humans. They had larger faces and jaws accompanied by pronounced sagittal crests in the case of males. Weaving all these various threads of evidence together into something cohesive can be an overwhelming task. Some of the specimens discussed above have only been recently announced, and most of them are still being worked on by the teams that discovered and described them, making it difficult for other researchers to independently assess them.
As a result, the evolutionary relationships between these different species are still in a state of flux. Various opinions have thus been expressed, and it really boils down to how one views variation within and between named fossil species. After the announcement of S. This could still be the case, but others have suggested that we are overestimating the level of species diversity in early hominin fossils and that Ardipithecus , Sahelanthropus , and Orrorin could very likely all belong to the same genus White In terms of a broader evolutionary context, again, it is still early days.
The team that discovered Ardipithecus has suggested that the evidence from Ethiopia and northern Kenya strongly point to a Ar. This is possible, but where Sahelanthropus and Orrorin might fit into the sequence remains to be seen. There is also the issue of Au. We find specimens as old as 4. So what can we definitively say about early hominins?
We have possibly as many as four species and three genera between 7 and 4. Twenty years ago, none of these species had been discovered or named, so we are doing well. The dating of these species coincides very well with the chimpanzee—modern human divergence dates predicted by molecular genetic work. All of them seem to exhibit adaptations to increased levels of bipedalism, but at least two genera Ardipithecus and Orrorin would have been very competent climbers as well.
We also see a reduction in canine size that might be associated with behavioral shifts in male competition and aggressive threat displays. Finally, and this we can be sure of, the hard work that goes into finding these specimens in often very remote places promises many more delights and surprises in the years to come. Aiello L, Dean C. An introduction to human evolutionary anatomy. London: Academic; Google Scholar. Begun D. The earliest hominins—is less more?
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