No skulls of Orrorin have been recovered, and so its cranial morphology and brain size are uncertain.

The proximal portion of the femur shows similarities to those of modern humans, suggesting the species was bipedal (Pickford et al. Orrorin is known primarily from postcranial fossils, including a partial femur. However, the position and orientation of the foramen magnum, the hole in the base of the skull through which the spinal cord passes, suggests that Sahelanthropus stood and walked bipedally, with its spinal column held vertically as in modern humans rather than horizontally as in apes and other quadrupeds (Zollikofer et al. Its brain size, 360cc, is within the range seen in chimpanzees, and the skull has a massive brow ridge, similar in thickness to male gorillas (Brunet et al. Sahelanthropus, dated to between 6 and 7 mya, is known from a largely complete skull and some other fragmentary remains. 2005) and Orrorin tugenensis from Kenya (Senut et al. The oldest hominins currently known are Sahelanthropus tchadensis from Chad (Brunet et al. The first human-like traits to appear in the hominin fossil record are bipedal walking and smaller, blunt canines. Some hominoid species from this period exhibit traits that are typical of humans but are not seen in the other living apes, leading paleoanthropologists to infer that these fossils represent early members of the hominin lineage. Early HomininsĬhanges from an ape-like anatomy are discernible in hominoid fossils from the late Miocene in Africa. Like living apes it would have walked quadrupedally (on all fours) when on the ground, and its diet would have consisted almost entirely of plant foods, primarily fruit and leaves. Moreover, the canines were probably sexually dimorphic, with males having much larger canines than females, as seen among the living great apes and Miocene fossils. The canine teeth were probably large and sharp, as seen in several Miocene hominoids. The HC-LCA would have had an ape-sized brain and body, with relatively long arms and fingers and a grasping foot that allowed it to forage in the trees. Nonetheless, we know from fossil and comparative evidence that it was much more similar to living apes than to living humans. These species varied in their anatomy and ecology, and it is not clear which, if any, of the fossil species discovered thus far represent the HC-LCA (Kunimatsu et al. There was a great diversity of ape species in the Miocene, with dozens of species known from the fossil record across Africa, Europe, and Asia.

Hominins are species on our branch of the hominoid tree after the split with the chimpanzee & bonobo line, including all of the extinct species and evolutionary side branches (Figure 1). The Human-Chimpanzee Last Common Ancestor (HC-LCA) is the species from which the hominin lineage and the chimpanzee & bonobo lineage diverged. In order to understand the evolution of any species, we must first establish its ancestral state: what sort of animal did it evolve from? For our lineage, this requires that we try and reconstruct the Last Common Ancestor of humans and chimpanzees (marked 'A' in Figure 1). We begin this discussion of our species' evolution in Africa, near the end of the geological time period known as the Miocene, just before our lineage diverged from that of chimpanzees and bonobos. The fossil record, along with studies of human and ape DNA, indicate that humans shared a common ancestor with chimpanzees and bonobos sometime around 6 million years ago (mya). Among the great apes, our closest relatives are the chimpanzees and bonobos (Figure 1). Our immediate evolutionary family is comprised of the hominoids, the group of primates that includes the 'lesser apes' (siamangs and gibbons) as well as the 'great apes' (chimpanzees, bonobos, gorillas, and orangutans). The implications are breathtaking if we could travel back far enough in time, we would find common ancestors between ourselves and every other living organism, from porcupines to flamingoes to cactuses. Darwin's great insight, and the unifying principle of biology today, is that all species are related to one another like sisters, cousins, and distant kin in a vast family tree of life.

Chimpanzee teeth facts