If you go to Stats, the labels for periods on the provided diversity curve shows both the full name of periods and the abbreviated letterlabels for the names of (some of) the periods, overlapping each other rather uncomfortably.
Here's an example, for the best class in the Metazoa:
My guess is that there's some rule that says that if there's enough room to print the full name of the period, but that rule isn't communicating to not print the abbreviated name in addition.
If you go to Stats, the labels for periods on the provided diversity curve shows both the full name of periods and the abbreviated letterlabels for the names of (some of) the periods, overlapping each other rather uncomfortably.
Here's an example, for the best class in the Metazoa:
My guess is that there's some rule that says that if there's enough room to print the full name of the period, but that rule isn't communicating to not print the abbreviated name in addition.