![]() Various researchers have suggested that the link between browridge size and sex is tenuous - thus, a more parsimonious conclusion is that the cranium belongs to a female individual (Wolpoff et al. The determination of the small relative size of the canine is dependent on the supposition that the cranium is male as inferred from its large browridges. There is, however, much contention that Sahelanthropus is a hominin based on these traits. However, there is much contention and their status as hominins is contested by various researchers in the field (Wolpoff et al. ![]() Bipedality is often considered to be the hallmark of hominins, and its presence in fossil species is often the key to their inclusion in the hominin clade. These earliest hominins lack derived features found in later hominins, and their inclusion in the hominin lineage is largely based on a reduction in canine size, absence of the C/P3 honing complex, and the presence of morphological adaptations for habitual or obligate bipedality generally found in the postcranial skeleton, particularly in the pelvis and hindlimb. 2002), and Ardipithecus kadabba (5.8-5.2 Ma, Haile-Selassie 2001, WoldeGabriel et al. 2002), Sahelanthropus tchadensis (7-6 Ma, Brunet et al. 1994) and soon after, even older hominins were discovered: Orrorin tugenensis (6.0-5.7 Ma, Pickford & Senut 2001, Senut et al. Their hard work and perseverance led to the discovery of several new genera and species of early hominins that are dated close to the estimated divergence dates for chimpanzees and humans. Driven largely in part by these new genetic-based hypotheses, there have been intensive efforts by different teams over the last two decades to find and explore sediments that record this crucial time period for which we had virtually no fossil evidence. The chimpanzee-human divergence date has been estimated to be between 8 and 5 million years ago (MA) since the 1960s through immunologic and molecular techniques (e.g., Steiper & Young, 2006). With the discoveries of the earliest hominin species discussed below, it is now possible to critically examine these assumptions. ![]() The similarities between the living African apes were thought to have been inherited from a common ancestor (=primitive features), implying that the earliest hominins and our last common ancestor shared with chimpanzees had features that were similar, morphologically and behaviorally, to the living African apes (Lovejoy 2009). But with the advent of molecular studies it has become clear that chimpanzees share a more recent common ancestor with humans, and are thus more closely related to us than they are to gorillas (e.g., Bailey 1993, Wildman et al. Gorillas and chimpanzees were commonly regarded to be more closely related to each other due to their high degree of morphological and behavioral similarities, such as their shared mode of locomotion - knuckle-walking. Until recently, the evolutionary events that surrounded the origin of the hominin lineage - which includes modern humans and our fossil relatives - were virtually unknown, and our phylogenetic relationship with living African apes was highly debated.
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