After watching all of the lecture videos for the week, traits varying between hominins and modern humans that caught my attention as important include big toe organization, size and shape of teeth, and arm length to leg length ratio.

Beginning with big toe organization, the opposability of the big toe in species such as Ardipithecus ramidus shows that these species continued to rely on the toes for grasping tree limbs and, therefore, spent less time walking bipedally than modern humans. Additionally, once Australopithecus afarensis was introduced to the paleoanthropologic world, researchers noticed the loss of the abductable big toe came in a species that had developed a pelvis designed for regular upright walking, suggesting that the opposable big toe was no longer needed when the organism began to walk on two legs–and therefore on the ground–more often than not. The gradual loss of the maneuverable big toe suggests the possibility of Australopithecus afarensis having the same common ancestor as humans since we do not see this feature in human feet–all five of our toes grow parallel to each other.

Another trait that researchers see much variance with among different genera of primates is tooth size and shape. In older genera, such as Ardipithecus and Australopithecus, the canine teeth are very large. We see small canines in humans as the sole purpose of these teeth is to chew food; in these ancient primates, canines are also used for fighting. Following primate genera chronologically from the past to more recent species, the canines gradually become shorter; additionally, the premolars and molars in these species become bigger to account for more diverse diets, adding more meat, seeds, et cetera. The prominence of large canines and underdeveloped molars in primates can tell us if the species were either very ancient ancestors of humans or, if these traits persist, do not share a common ancestor with humans at all.

Finally, the arm length to leg length ratio in primates gives us an idea of which species spent more time in the trees and which species spent more time walking bipedally. In the genus Orrorin and the first species of Australopithecus, long ape-like arms are apparent as neither of these genera were fully bipedal; the long arms were still necessary to hang from trees and swing from branch to branch. However, as we see in more recent species, such as Australopithecus garhi, the arm to leg ratio begins to look more like that of modern humans in which the legs are significantly longer than the arms. Seeing as we already know that Australopithecus garhi was bipedal, the increasing arm to leg ratio concludes that the reduced need for long arms resulted in them becoming shorter in comparison to the legs, which bear more weight in bipedal creatures compared to quadrupedal ones.

All of the evidence listed above was discovered by in-depth investigation of fossilized skeletal remains found in Africa and other locations where prehistoric hominins lived. Without fossils, it would be immensely difficult to catalog the features of these ancient primate genera as most, if not all, of these species are extinct presently; additionally, there obviously were no forms of technology invented at these times where information concerning these species could be documented, so fossils are the only gateway to finding more information on these organisms.