Final answer:
Orrorin tugenensis is considered a hominin due to anatomical evidence of bipedalism, such as a larger femoral head and muscle attachments indicative of upright walking, as well as teeth resembling those of modern humans.
Step-by-step explanation:
Why Orrorin tugenensis is Considered a Hominin
Orrorin tugenensis, discovered by Martin Pickford and Brigitte Senut in Kenya in 2001, has several characteristics that place it within the hominin family. The most significant trait suggesting its status as a hominin is the evidence of bipedalism. The anatomy of Orrorin's femoral head is larger than that of quadrupedal apes, indicating that it was likely capable of supporting an upright posture and the weight of the upper body - a hallmark of hominin locomotion. Additionally, the muscle attachments on the femur and the structure of the teeth, including thick dental enamel and small, square molars, align more closely with those of modern humans rather than non-hominin primates. These traits are suggestive that Orrorin tugenensis moved on two legs and may be one of the earliest human ancestors, predating even the australopithecines which were once considered our earliest known relatives.The discovery of Orrorin challenges previous understandings of human evolution, suggesting that the lineage leading to humans may have become bipedal earlier than previously thought. This could mean that the australopithecines are not in the direct lineage of modern Homo sapiens, with Orrorin being a potential ancestor. Fossil records and further examination of specimens are essential in piecing together our evolutionary history, which has significant implications for our understanding of the origin of bipedality.