Since the researcher was reconstructing the evolution of a protein I would say the date was determined using a technique called the molecular clock: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Molecular_clock" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Molecular_clock</a><p>That and the rise of multi-cellular life marks the beginning of the Cambrian explosion (542M years ago). That gives 60M years for the mutation to spread and specialize.