A bottom-up perspective on ecosystem change in Mesozoic oceans

Area of Science:

• Paleontology
• Marine Biology
• Evolutionary Biology

Background:

• Mesozoic and Early Cenozoic marine fauna show evolutionary trends in morphology, distribution, and behavior.
• These trends are often attributed to increased predation pressure from durophagous (shell-crushing) predators.
• A concurrent, less recognized shift in marine ecosystems involved phytoplankton evolution.

Purpose of the Study:

• To investigate the impact of phytoplankton evolution on marine ecosystems and animal evolution.
• To evaluate how changes in phytoplankton composition influenced trophic dynamics and evolutionary pressures.

Main Methods:

• Analysis of fossil records, biomarker molecules, and molecular clocks to reconstruct phytoplankton composition changes.
• Utilizing ecological and biogeographical models developed for modern phytoplankton to simulate past ecosystem dynamics.
• Modeling the consequences of phytoplankton radiations on primary production transfer to higher trophic levels.

Main Results:

• Fossils, biomarkers, and molecular clocks confirm a major shift in phytoplankton, including the rise of mixotrophic dinoflagellates, coccolithophorids, and diatoms.
• Phytoplankton radiations, particularly of mixotrophic dinoflagellates and diatoms, are modeled to have enhanced the transfer of primary production to larger size classes and higher trophic levels.
• This accelerated energy transfer provides a mechanism for the observed evolutionary shifts in marine animals.

Conclusions:

• Phytoplankton evolution played a crucial role in shaping Mesozoic and Early Cenozoic marine ecosystems.
• The diversification of phytoplankton, especially diatoms, facilitated evolutionary changes in marine animals by altering food web dynamics.
• Phytoplankton evolution offers a complementary explanation for observed secular trends in marine animal evolution alongside predator-prey dynamics.