What species first appeared to walk upright?

The first species that appeared to walk upright was the Australopithecus.

Explanation:

Australopithecus was an extinct genus of hominins that lived in Africa between 4.2 and 2 million years ago.

The Australopithecus presented both ancestral characters (little bulky brain) and derived characters (teeth close to that of the genus Homo). Their locomotion was generally mixed, and associated a form of bipedalism with an ability to climb still marked. It is possible that one of the Australopithecus species is at the origin of the genus Homo, which appeared in Africa between 3 and 2 million years ago.

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