Walking upright on shorter legs
This 4.1 million year old upper tibia (shin bone) fossil, KNM-KP 29285, comes from Australopithecus anamensis, an early human species that lived near open areas and dense woods. Their bodies had evolved in ways that enabled them to walk upright most of the time while still being able to climb trees. As a result, they could take advantage of both habitats. The top part of the tibia (where the lower leg meets the knee) is concave, or depressed from stress. This shows that the individual often put weight on the bone—evidence of standing upright. The lower part of the tibia (where the lower leg meets the ankle) is wider or thicker—evidence that it acted as a type of shock absorber as this individual walked .