It took a team effort to put this skeleton together.
Knowledge of skeletal anatomy is useful when trying to understand the shapes of bones in relation to their function and position in the body. When we compare the skeletons of extinct species to what we know about extant skeletons, we can see how they are similar and different and what that might mean about their function in the past (e.g., is the pelvis shaped so that the individual walked on all fours or on two legs?).
The fossil record of our human ancestors tells a long and complicated story. The origins started somewhere between 6 to 7 million years ago in Africa. Hominins are primates just like species of Pan, Gorilla, and Pongo. However, hominins are distinguishable from these other groups in two key anatomical features: smaller canine teeth, and skeletons that facilitate bipedal locomotion (walking on two legs). These features might indicate changes in diet, more dependence on tool use, efficient terrestrial mobility and even new systems of heating and cooling the body.
Fossils finds of the earliest hominins are rare because they are difficult to preserve over such a vast amount of time. However, we have several specimens that point to about 5 early hominin species (that we know of for now…). Sahelanthropus tchadensis, Orrorin tugenensis, Ardipithecus ramidus, Australopithecus anamensis, and Australopithecus afarensis all display bone morphology that suggests bipedal locomotion – but with different degrees of certainty. The bipedal locomotion that these species had was much different from that of our own, or even of later hominins. Anatomical evidence suggests that these species’ bipedal locomotion was less efficient, and that they maintained the ability to move around in trees better than fully bipedal hominins (like us) can. Overall, the evolution of bipedalism is important as it is likely related to increased movement on the ground (instead of in the trees), increased aridity in the surrounding environment (more open landscapes to traverse) and for thermoregulation (cooling down larger brains and bodies that may be moving around more often).
Sites in the Turkana Basin boast many important hominin discoveries, including Australopithecus anamensis (4.2 million years old), Australopithecus afarensis (about 3.3 million years old), Kenyanthropus platyops (3.5-3.2 million years old), Paranthropus aethiopicus (about 2.6 to 2.3 million years old), and Paranthropus boisei (about 2.3-2 million years old). While none of these hominins belong to our genus Homo, they tell a very interesting story of hominin evolution during a period of time when species diversity increased. It is likely that several of these species lived contemporaneously in the same regions, and so likely filled their own niche.
Just after 3 million years ago we see the appearance of the earliest hominins that share our genus Homo in eastern Africa (finds in Ethiopia and Kenya provide the earliest examples). One of the most famous specimens found west of the Lake Turkana is a nearly complete juvenile skeleton of Homo erectus known commonly as the “Nariokotome Boy” skeleton (dating to about 1.6 million years ago). When it was discovered, it was the first nearly complete skeleton of this species. It provided a lot of important information about increasing efficiency in hominin bipedal locomotion, growth rates in juveniles, and overall information about changes in stature.
Species of hominins in the Homo lineage continue to diversify and change from about 1 million to 300,000 years ago in ways that paleoanthropologists are still working to get a handle on. What does this species diversity mean? How much diversity is there within and between these species? How many species were there? We need more hominin fossil finds from this time period to really figure it all out. Finally, we see the emergence of Homo neanderthalensis in Eurasia (commonly known as “Neanderthal”) and then of our species, Homo sapiens between 300 – 200,000 years ago.
Figuring out the number of species and the diversity within and between them takes a lot of analytical work. The TBI students tried their hand at comparing features of hominin crania and mandibles from all periods of human evolution. Their task was to describe the variation within certain features (e.g., cranial capacity or tooth shape and size) using casts.