A ubiquitous ~62 Myr periodic fluctuation superimposed on general trends in fossil biodiversity: II, Evolutionary dynamics associated with periodic fluctuation in marine diversity

We investigate evolutionary dynamics related to periodicity fossil biodiversity. Coherent periodic fluctuation in origination/extinction of marine genera that survive <45 million years is the source of an observed ~62 million year periodicity analyzed in Paper I. We also show that the evolutionary dynamics of “long-lived” genera (those that survive >45 million years) do not participate in the periodic fluctuation in diversity and differ from those of “short-lived” genera. The difference between the evolutionary dynamics of these 2 genera classes indicates that the periodic pattern is not an artifact of variation in quality of the geologic record. The interplay of these two previously undifferentiated systems, together with the secular increase in abundance of “long-lived” genera, is probably the source of heretofore unexplained differences in evolutionary dynamics between the Paleozoic and post-Paleozoic as reported by others. Testing for cycles similar to the 62 Myr cycle in fossil biodiversity superimposed on the long-term trends of the Phanerozoic as described in Paper I, we find a significant (but weaker) signal in sedimentary rock packages, particularly carbonates, which suggests a connection. The presence of a periodic pattern in evolutionary dynamics of the vulnerable “short-lived” component of marine fauna demonstrates that a long-term periodic fluctuation in environmental conditions capable of affecting evolution in the marine realm characterizes our planet. Coincidence in timing is more consistent with a common cause than sampling bias. A previously identified set of mass extinctions preferentially occur during the declining phase of the 62 Myr periodicity, supporting the idea that the periodicity relates to variation in biotically important stresses. Further work should focus on finding links to physical phenomena that might reveal the causal system or systems.

💡 Research Summary

The paper builds on the authors’ earlier work (Paper I) that identified a ∼62‑million‑year (Myr) periodicity superimposed on the long‑term trend of marine fossil biodiversity. Here the authors dissect that signal at the level of evolutionary dynamics by separating marine genera into two classes based on their average lifespan: “short‑lived” genera that typically persist for less than 45 Myr and “long‑lived” genera that survive longer than 45 Myr. Spectral analyses reveal that the short‑lived group exhibits a coherent oscillation in both origination and extinction rates that matches the 62‑Myr cycle, whereas the long‑lived group shows no such periodicity. This dichotomy demonstrates that the cycle is not an artifact of uneven sampling or changes in the quality of the geological record, because the two groups are recorded in the same strata but behave differently.

To test whether the periodicity might be reflected in the rock record itself, the authors examined the timing of sedimentary packages, especially carbonate deposits. A weaker but statistically significant 62‑Myr signal appears in carbonate sequences, suggesting that the periodic environmental driver left an imprint in the depositional environment as well as in the biota. Moreover, previously identified mass‑extinction events tend to cluster on the declining phase of the cycle, reinforcing the idea that the periodic fluctuation corresponds to intervals of heightened biotic stress.

The study also documents a secular shift in the composition of marine fauna: during the Paleozoic short‑lived genera dominate, and the 62‑Myr rhythm is pronounced; in the post‑Paleozoic the proportion of long‑lived genera rises, the overall diversity increases, and the periodic signal becomes muted. This transition helps explain earlier reports of differing evolutionary dynamics between the two eras.

Finally, the authors argue that the most plausible explanation for the 62‑Myr rhythm is a real, planet‑wide oscillation in environmental conditions—potentially linked to tectonic cycles, sea‑level changes, climate oscillations, or astronomical phenomena such as the solar system’s vertical motion through the Galactic plane. The coincidence of the biological cycle with a weak carbonate‑rock signal favors a common cause over sampling bias. The paper concludes by calling for interdisciplinary work to pinpoint the physical mechanism(s) that generate this long‑term periodicity and to assess their impact on marine evolution.