Around the year $2000,$ a flurry of fossil discoveries in Africa resulted in fierce debates about the earliest hominins. These discoveries from Kenya, Ethiopia, and Chad ranged in age from $5\mathrm{.}2$ to $7$ million years old and, according to some researchers, reflect characteristics associated with bipedalism. The oldest of these, called $\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_,$ includes a partial cranium that researchers say preserves the location of the foramen magnum at the base of the skull. The position of the foramen magnum is one of the key features researchers use to determine whether a fossil primate was bipedal.$$

Orrorin tugenensis

Sahelanthropus tchadensis

Australopithecus sediba

Ardipithecus kadabba