Human Evolution -- Sahelanthropus tchadensis

The first humans after the human-chimp splint (YouTube):

Oldest to youngest:

The earliest potential hominin is Sahelanthropus tchadensis, discovered in Chad and dated to between 7 and 6 million years ago. While earlier analyses of its skull suggested bipedalism, more recent studies of postcranial bones (like the femur) propose it was not adapted to walking on two legs, leading to debate about whether it was a true hominin or if bipedalism developed later in the human lineage.

Orrorin tugenensis, meaning "original man," is a fossil species from around 6 million years ago, discovered in Kenya in 2000, that is considered one of the earliest possible hominins (human ancestors). The species' defining feature is its femur (thigh bone), which shows adaptations for bipedalism (upright walking), suggesting that upright walking may have evolved very early in the hominin lineage. However, the precise phylogenetic position of Orrorin is still debated, with some researchers placing it as an early ancestor to modern humans and others suggesting it might have been an evolutionary offshoot or a relative of the robust australopithecines.

The Ardipithecus genus, containing the species Ardipithecus kadabba and Ardipithecus ramidus, represents a group of early hominins from Africa that lived between approximately 5.7 and 4.4 million years ago. While not necessarily a direct human ancestor, Ardipithecus is important for its intermediate traits, such as a mosaic of features for both upright walking and climbing in wooded environments, which offer insights into human evolution after the split from our chimpanzee ancestors.

Australopithecus was a diverse group of extinct, ape-like hominins living in Africa between 4.4 and 1.4 million years ago, known for bipedal (upright) walking and large molar teeth but with relatively small brains. These "southern apes" are crucial to human evolution, as they were the ancestors of the Homo genus, though the specific ancestral species is debated. Key species include the famous "Lucy" (Australopithecus afarensis), whose fossils confirmed that bipedalism predated the evolution of large brains.

Kenyanthropus is a genus of early human ancestors that lived in Africa about 3.5 million years ago, contemporary with Australopithecus afarensis ("Lucy's species"). Discovered in 1999, Kenyanthropus platyops is known for its unusually flat face and small molars, traits that distinguish it from Australopithecus and suggest greater diversity in the human family tree at that time. While some researchers view Kenyanthropus as a distinct genus, others argue it represents a Kenyan variant of A. afarensis, with its unique features potentially linked to the distorted nature of the fossil evidence.