Final answer:
The 4.2-3.9 million-year-old specimen found in Kenya likely refers to members of the species Australopithecus afarensis, crucial to understanding human evolution.
Step-by-step explanation:
The specimen found in Kenya that dates back to 4.2-3.9 million years ago (mya) likely refers to members of the species Australopithecus afarensis. The most famous finding of this species is "Lucy," the partial skeleton dating to around 3.75-2.8 mya. Although Lucy was discovered in Ethiopia, additional Australopithecus afarensis specimens have since been found in Kenya. These early hominins are characterized by traits that suggest bipedalism, such as their pelvic structure and leg bones, and have made important contributions to our understanding of human evolution.