(Berkeley Lab Research News)
In examining their results, Muller and Rohde found that the fossil diversity cycle is most evident when only short-lived genera (those that survived less than 45 million years) are considered. They also found that some organisms seem to be immune to the cycle, while others are exceptionally sensitive. For example, corals, sponges, arthropods and trilobites follow the cycle, but fish, squid and snails do not. In general, longer-lived genera that are more diverse and widespread stand a better chance of resisting the 62 million year cycle.
That should explain the hippies.