Course: Intro to Physical Anthropology 1111
There is much ambiguity in the fossil record of which species are believed to qualify or not qualify as hominins. This is because there is much variation in the morphological features in these fossils which creates controversy in determining evolutionary relationships with potential ancestors with anatomically modern humans. Characteristics paleoanthropologists look for to distinguish what species to be considered a hominin are bipedalism, skull features and larger brains. Bipedalism is an important characteristic to be evaluated in hominins because it was a favorable trait in locomotion when there was climate change in Africa which resulted in loss of vegetation, which made being arboreal a useless trait in locomotion in that environment. Also with bipedalism we could look at the feet of what are believed to be early hominins, and then compare it to the foot structure of an anatomically modern human. If the foot does not meet the criteria or come close to the structure of a Homo sapiens (in terms of being shock absorbant, toes lines together and arched), we could distinguish if the compared potential hominin to be a direct ancestor or perhaps if it may have branched off into its own species. The second important characteristics that paleoanthropologists consider when distinguishing what is an ancestor to Homo sapiens is skull structure. Despite the skull being a smaller portion of our body, it actually presents most of the variations in morphological features when comparing to early hominins. Some of the features that are looked at in the skull are presence of prognathism, mental eminence (chin), reduced canines, reduced sagittal crest, sagittal keel (torus), brow ridge and orbital bone shape (are they round, rectangular, etc). The last characteristic that helps suggest evolutionary relationships is brain size. Knowing that anatomically modern Homo sapiens sapiens possess large brains, we can try to trace what are thought to be our ancestors by observing and comparing cranial capacity and trend of a growing brain over time. With a growing brain comes a greater length in intelligence, evidence for this can be tool use, diet (hunting) and also cultural behaviours (burial, hearths, etc.).
With these three characteristics we can attempt to determine which species are qualified to be hominins and those who are not. The first species to be examined which is not a hominin is Paranthropus aethiopicus, Paranthropus boisei, Paranthropus robustus. This group of species existed around 2.5 million to 1.1 million years ago. They present many primitive traits such as pronounced prognathism, presence of a sagittal crest and a small cranial capacity (which is around 400-500 cubic centimeters). This species is believed to have branched off of the species Australopithecus afarensis but when branching had primitive traits that over a long period of time still remained. Such as a large sagittal crest and cranial capacity which did not increase shown in skull fossils found by paleoanthropologists (specifically in the skull of the Paranthropus aethiopicus, aka “black skull”). One trait which did progress was growth in the size of their skull structure, but more specifically mandible size and strength. This is because their diet consisted of very hard or dense vegetation which was pretty much inedible to any other existing species (Marable, 2000)However having a diet being very specific did not end up to work in their favor in the long run because around 1.2 million years ago Africa underwent some serious climate change which effected their niche (which was dense vegetation) by creating an environment where their food did not grow and with a small brain and very specific features in terms of diet they were not able to adapt to their immediate surroundings. The second species which is believed not to be a hominin is the Homo rudolfensis. The Homo rudolfensis