Australopithecus afarensis (Johanson, White and Coppens 1978; 3.3-2.6 mya, females: 3.7 feet tall, males 5 feet tall.)
Australopithecus had a larger skull and a bigger brain. The feet were more like those of Homo without the diverging toe found in more primitive primates from Notharctus to Ardipithecus.
Loss of quadrupedalism meant babies could no longer go along for a ride on their mother’s back. Now they had to be carried. Bipedalism permitted this. Soon australopithecines were carrying tools, sticks, and anything they wanted to keep or hoard, even a second infant. Human reproductive rate is five times that of chimps.
Hair on the face and top of the head does not fall out but keeps growing as a sort of sun cap. Elsewhere hair thins, exposing more skin. Sweating develops for evaporative cooling.
If you want to read the book, "From the Beginning - The Story of Human Evolution" by David Peters (Little, Brown 1991), which is where the above images were first published, click here for the PDF.