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The seas of the Paleozoic Era were quite different from today, and between them, there was a great ecological transition. This episode, we discuss the complexities, mysteries, and lasting impacts of the Mesozoic Marine Revolution.
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Changing Seas
The Mesozoic Marine Revolution (MMR), as the name implies, was a major restructuring of ecosystems, particularly in shallow oceans, during the Mesozoic Era. It marks the transition from the characteristic ocean ecosystems of the Paleozoic to the style of marine ecosystems we know today. The concept of the MMR was formalized in the 1970s, with studies revealing a dramatic shift in the makeup of marine fossils, and it remains a major topic of research today, as scientists continue to explore the nuances of this many-faceted transition.
Image by Ria Tan, CC BY-NC-ND 2.0
The most famous players of the ecological drama of the MMR are many varieties predators and prey. The fossil record reveals a major increase in diversity of predators specialized for eating hard-shelled prey. These include species with crushing mouthparts, such as certain fish, as well as species with drilling mouthparts, like many snails and cephalopods, which bore holes in shells to access the nutrition within. In addition, the MMR also sees a corresponding diversification of shell defenses among marine invertebrates. The MMR also displays an increase in trace fossil evidence of bioturbation, including burrowing and scraping of seafloor substrates. And along with all of that, this time period features diversification of many important modern lineages of marine fish and invertebrates.
Top left: A moon snail, a type of naticid snail. Image by Nick Hobgood, CC BY-SA 3.0
Bottom left: Holes in modern bivalve shells drilled by naticid snails. Image by BathyMetrix, CC BY-SA 4.0
Right: A predatory boring hole in a Miocene fossil shell. Image by James St. John, CC BY 2.0
The MMR isn’t just one event, but a long series of ecological changes over many millions of years, and the causes of the transition are likely complex. The breakup of Pangaea might have helped get things moving by creating vaster regions of nutrient-rich shallow oceans. Predation seems to have been a major driving pressure for the evolution of specialized diets, active lifestyles, and anti-predatory defenses, although it’s possible there were other factors driving changing lifestyles, such as new reproductive strategies or increased availability of nutrients. These many factors are the focus of ongoing research to this day.
Learn more
The Mesozoic Marine Revolution rewrote the script of the ocean
Hunting evidence for the Mesozoic Marine Revolution (technical, open access)
Infaunalization and resource partitioning during the Mesozoic marine revolution (technical, open access)
Love, not war, drove the Mesozoic marine revolution (technical, open access)
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If you enjoyed this topic and want more like it, check out these related episodes:
- Episode 9 – The Cambrian Explosion
- Episode 36 – Reefs
- Episode 45 – The Permian Extinction
- Episode 171 – The Tethys Sea
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