Size and Weight:
Notharctus appeared on the scene only 10 million or so years after the dinosaurs went extinct, but we can already see in this tiny prehistoric primate many of the unique qualities that would lead to human beings tens of million of years later: a relatively flat face with forward-facing eyes, hands flexible enough to grab onto branches, a long, sinuous backbone, and (last but not least) a bigger brain, proportionate to its size, than any previous vertebrate. (Recently, researchers discovered that Notharctus possessed a "grooming claw" on the second digit of its hands.)
However, it's important not to overstate Notharctus' similarity to modern humans, or even our immediate hominid ancestors. This ancient creature still led a timid, lemur-like lifestyle, high up in the branches of trees (the better to avoid the giant megafauna mammals of its day), and fed opportunistically on fruits, seeds and insects. Also, Notharctus doesn't seem to have been directly ancestral to humans, though one of its close relatives surely lay at the base of the Homo sapiens family tree.