Factors Affecting Hominin Evolution Before 5 Million Years Ago: The Introduction of the Australopithecines

Some 5 million years ago during the beginning of the Pliocene Epoch climatic changes were causing African forests to progressively reduce their geographic coverage as grasslands, or savannas were advancing across the landscape.the genealogy of apes and human like creatures begin to leave a fossil record that signaled and divergence and the beginnings of separate developmental path.

Hominids were represented by the emergence of the genus australopithecines (southern ape) of which several varieties developed over time and emerged from the South African region as demonstrated by the many fossil findings in the proximate Great Rift Valley. These fossil findings showed that early hominins had almost human-like bodies below the neck but brains that were very little changed in size from those of apes. This point has been established in our previous postings but needs to be re-established to set the scene for the bifurcation of the australopithecine lineage into at least 2 evolutionary lines of hominins descended from the early australopithecines.

One line, often referred to as the gracile or slim and slender form included Australopithecus anamensis, Australopithecus africanus and Australopithecus afarensis. A. africanus and A. afarensis apparently were 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 lineage, referred to as the robust forms which included types such as Australopithecus aethiopicus, Australopithecus boisei and Australopithecus robustus lived more in mixed grassland and woodland environments, was primarily vegetarian much the same as their australopithecine fore bearers and had become extinct by about a million years ago.

What all australopithecines had in common among each of the various varieties, was a preference for bipedalism. In addition, they may also have used sticks and stones to fight, for they did not possess the type of canine teeth that would have made very imposing. Australopithecine brain cases were only capable of holding approximately 35% of the total volume that a modern human can contain. Australopithecines stood approximately four and a half feet tall. A very important point to consider about the Australopithecines was that their bipedalism came before the development of large brains, a factor long thought to be quite the opposite for many researchers and scientists.

Upright Standing Hominids With Ape-Like Brains During the Miocene

Now that we have established that the hominids of some 7 million years ago living during the Miocene period (the entire Miocene era spanned 24 to 5 million years before the present, or mybp) had similar behavioral patterns found in contemporary chimpanzees, we can delve further into the great apes and hominids of that time in the past.

Anoiapithecus brevirostris, whose remains of a jaw and of a great ape's face are shown at the top of this post is a recently discovered collection of bones found from the Abocador de Can Mata site in Spain. A paper recently published in the journal PNAS under the title, “A unique Middle Miocene European hominoid and the origins of the great ape and human clade.” Points out that "this hominoid, aptly named Lluc or enlightenment in Latin, is that it has a very modern face… In other words it's got a reduced facial prognathism (having a protrusion of the jaws, bulging of the jaws). The specimen includes a fragmented cranium that with most of the face preserved and the associated mandible. While the muzzle of Lluc is so reduced that only find comparable values within the genus Homo, Lluc's got an array of primitive features, such as super thick dental enamel and teeth with bulbar cusps. The mandible is also very robust. All of which are characteristics of afropithecids — primitive hominoids from the African Middle Miocene.

The authors explain: "But other more derived features, like the forward positioning of the zygomatic bone and a bold mandibular torus along with a a reduction in the maxillary sinus, are shared only with the kenyapithecines. Kenyapithecines are a group of apes that ever dispersed outside the African continent and colonized the Mediterranean region, by about 15 million years ago, and are collectively grouped in the genera Kenyapithecus and Griphopithecus.

They continue: "Ultimately, you can see how this specimen (IPS43000), Anoiapithecus brevirostris, has a combined a set of features that until now had never been found from the fossil record. The array of features allows us enables to identify two possibilities to be the ancestral form to our family (Kenyapithecus and Griphopithecus). The authors take a leap of faith here arguing that when one takes into account that these two genera cannot be considered members of the family Hominidae yet, because they lack its basic diagnostic features, they find it obvious that the origin of our family is a phenomenon that took place on the Mediterranean region during the time span comprised between their arrival from Africa by about 15 Ma, and about 13 Ma, when we began to find in els Hostalets the first members of our family.

The authors say: "But other more derived features, like the forward positioning of the zygomatic bone and a bold mandibular torus along with a a reduction in the maxillary sinus, are shared only with the kenyapithecines. Kenyapithecines are a group of apes that ever dispersed outside the African continent and colonized the Mediterranean region, by about 15 million years ago, and are collectively grouped in the genera Kenyapithecus and Griphopithecus.

Summing up their findings, the authors conclude: "Ultimately, you can see how this specimen (IPS43000), Anoiapithecus brevirostris, has a combined a set of features that until now had never been found from the fossil record. The array of features allows us enables to identify two possibilities to be the ancestral form to our family (Kenyapithecus and Griphopithecus). The authors take a leap of faith here arguing that when one takes into account that these two genera cannot be considered members of the family Hominidae yet, because they lack its basic diagnostic features, they find it obvious that the origin of our family is a phenomenon that took place on the Mediterranean region during the time span comprised between their arrival from Africa by about 15 Ma, and about 13 Ma, when we began to find in els Hostalets the first members of our family."

It is classified as a great ape with many afropithecid and several kenyapithecine features that the European Guide To Science Journalism Training explains: "The morphological studies carried out on the fossil remains prove the presence of physical features which are typical of modern hominids (such as the nasal opening is very wide behind, a high position of the root of the zygomatic arch and a very deep palate). These are associated with primordial and derived features (such as a thick dental enamel, a morphology of globular dental cusps and a strong jaw) especially of those great apes from Middle Miocene of Africa named "Afropitecidi". An artist's reconstructive drawing of Anoiapithecus brevirostris is shown below.

The European Guide To Science Journalism Training continues: "Apart from these distinctive elements, there are other characteristics that have never reached the countries of the Mediterranean Europe. They are: the fore position of the zygomatic arch (formed by the (a bone extending forward from the side of the skull, over the opening of the ear) and the temporal process of the zygomatic (the side of the cheekbone), the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process of the mandible), a very protruding mandible and a very reduced jawbone breast which are specific of the African Kenyapithecines (Kenyapitecus and Griphopithecus).

The European Guide To Science Journalism Training concludes: "It is possible to assume that our origins must be likely searched in the Mediterranean area and not in the African area as it has always been thought of. In truth, the researchers, responsible for the discovery, admit that hominids can be diversified in Eurasia, starting from the Kenyapithecines ancestors - of African origins - evolving later into Pongidae (chimpanzees, gorillas and orangutans) and Homininae (Homo genre and African great apes)."

Above are the skeletal remains of "Pierolapithecus catalaunicus, a Miocene hominoid from Spain ... What's special about it is that it appears to be the closest thing to a last common ancestor of all of the great apes. In an article Moyà-Solà S, Köhler M, Alba DM, Casanovas-Vilar I, Galindo J (2004) Pierolapithecus catalaunicus, a New Middle Miocene Great Ape from Spain. Science 306(5700):1339-1344., the following abstract is provided:

"We describe a partial skeleton with facial cranium of Pierolapithecus catalaunicus gen. et sp. nov., a new Middle Miocene (12.5 to 13 million years ago) ape from Barranc de Can Vila 1 (Barcelona, Spain). It is the first known individual of this age that combines well-preserved cranial, dental, and postcranial material. The thorax, lumbar region, and wrist provide evidence of modern ape–like orthograde body design, and the facial morphology includes the basic derived great ape features. The new skeleton reveals that early great apes retained primitive monkeylike characters associated with a derived body structure that permits upright postures of the trunk. Pierolapithecus, hence, does not fit the theoretical model that predicts that all characters shared by extant great apes were present in their last common ancestor, but instead points to a large amount of homoplasy in ape evolution. The overall pattern suggests that Pierolapithecus is probably close to the last common ancestor of great apes and humans."

The distinguishing characteristic between the early hominids and the great apes was focused on two things: the reduction of canine teeth and the ability of upright posture while walking. And it seems that woodland habitats were closely associated with the hominid transition to upright locomotion. Being upright allowed the hominids to see above the tall grasses of the grasslands that surrounded the trees and the upright positioning of the hominid became most pronounced with the arrival of Homo erectus. A second thought behind the changeover to upright posture is that it exposed the hominid to less heat from the sun. In addition, a loss of body hair was taking place at the time of erectus because less hair allowed for the transference of sweat that was no longer trapped by excess body hair and thus allowed for more efficient cooling of erectus. So the habitat which allowed for the evolutionary transition of hominid was the area between the grasslands and forests and certainly brought about a change in diet since there were more carcasses of animals strewn about the grasslands because that was the killing territory of the big cats. Additionally, the shrinking of the hominid canines was important because the apes kept theirs for fighting amongst themselves while the hominids, who often subsisted on vegetative materials such as tbers and bulbs had a greater need for more compact canine teeth. But remained pretty much constant throughout the period was the maintenance of brain sie as brains in hominids did not increase in size for several million years.

In many ways the Homo lineage was a spin-off of the lineages of the great bipedal woodland apes who evolved into larger sized creatures who were vegetarians and eventually died out after about of a million years as they reached an evolutionary deadend. Meanwhile the omni-vore characteristics of Homo allowed for continued growth. And that is where the next installment will pick up.