Basal Hominins
Species of Basal Hominins
Basal Hominins are our earliest human ancestors, the closest to our last common ancestor (LSA) with chimpanzees. Three species (or four, depending on how you count them) have been found:
Sahelanthropus tchadensis:
See the fossils here
Found: in Chad (central Africa)
Date: 6-7mya (based on biostratigraphy)
Condition of fossils: only one skull was found, plus a number of smaller fragments
Evidence that it is a hominin: foramen magnum is forward under the skull, more so than in a chimpanzee
Orrorin tugenensis
See the fossils here
Found: in Kenya
Date: 6mya (based on K/Ar dating)
Condition of fossils: two femurs, plus a number of smaller fragments. No skulls have been found.
Evidence that it is a hominin: the femur shape is similar to later bipeds
Ardipithecus ramidus (some researchers put the earlier Ardipithecus specimens into a different species, Ardipithecus kedabba)
See the fossils here
Found: in Ethiopia
Date: 4.5mya
Condition of fossils: there are hundreds of fossils from at least three different sites, and these fossils include nearly complete skeletons. This is the best-known of the basal hominins.
Evidence that it is a hominin: femur shape, pelvis shape, and position of foramen magnum all show it was a facultative biped
Basic Conclusions from Basal Hominin Finds
They lived in mixed woodland and grassland environments in Central and East Africa
They had a chimp-sized brain (translation: small)
They had lest robust skulls than modern chimps, with flatter faces and fewer crests
Their teeth already show smaller, more human-like canines
They had long fingers and arms for climbing
They were facultative bipeds (not obligate bipeds). In other words, they were able to walk bipedally when it was convenient to do so, and they probably did a lot of the time. But they could also walk and climb more like an ape.
They had long, curved toes and an opposable big toe for climbing
their pelvis had longer ischium than ours (better leverage for climbing, more like a quadruped)
but their pelvis had a ilium more like ours, short and curved forward, rather than long like an ape's
overall, they were better bipeds than modern chimpanzees, not as good as modern humans