Truncated bimodal latitudinal diversity gradient in early Paleozoic phytoplankton

The latitudinal diversity gradient (LDG)-the decline in species richness from the equator to the poles-is classically considered as the most pervasive macroecological pattern on Earth, but the timing of its establishment, its ubiquity in the geological past, and explanatory mechanisms remain uncertain. By combining empirical and modeling approaches, we show that the first representatives of marine phytoplankton exhibited an LDG from the beginning of the Cambrian, when most major phyla appeared. However, this LDG showed a single peak of diversity centered on the Southern Hemisphere, in contrast to the equatorial peak classically observed for most modern taxa. We find that this LDG most likely corresponds to a truncated bimodal gradient, which probably results from an uneven sediment preservation, smaller sampling effort, and/or lower initial diversity in the Northern Hemisphere. Variation of the documented LDG through time resulted primarily from fluctuations in annual sea-surface temperature and long-term climate changes.

Automated summary

Researchers have found that the latitudinal diversity gradient (LDG) was exhibited by marine phytoplankton from the beginning of the Cambrian period, with a diversity peak centered in the Southern Hemisphere instead of the equator. This LDG is likely a truncated bimodal gradient, possibly due to uneven sediment preservation, inadequate sampling effort, and/or lower initial diversity in the Northern Hemisphere. Variation in the LDG over time is primarily attributed to fluctuations in annual sea-surface temperature and long-term climate changes.