Question

A research partner invites you to study some new fossils they've collected from their site in Tanzania. When you ask how old the site is, they tell you that they're not sure because they have not been able to absolutely date any of the volcanic tephras. At the museum, you look at fossils from the site and identify Kolpochoerus olduvaiensis, Loxodonta sp., Equus sp., Kolpochoerusmajus, and Parmularius rugosus. About how old is the site?

Answer 1

The site can be old anywhere in the range between 1.78 and 550,000 years.

The reason why the site's age will be in this range is that the species that are represented in it have all lived in this time frame. To put up more or less than those numbers, will make no sense as some of those species would have been absent.

While some have existed since much earlier than 1.78 million years ago, and others still exist today, it will not make any sense to lift or lower the age range, as some of the species haven't evolved prior to that, or some went extinct in meantime.