Study shows ancient reef-building stromatoporoids escaped extinction, at least temporarily

Are modern coral reefs going extinct? The answer is uncertain, but some of their ancient counterparts have managed to escape such a threat, at least for a while.

Scientists at Osaka Metropolitan University have discovered that ancient reef-building organisms called stromatoporoids survived the Late Devonian mass extinction and continued to thrive as major reef builders long after their presumed extinction.

These results, published in Geologyshed light on how life on Earth has responded to past environmental changes, providing valuable insights into the resilience and adaptability of marine ecosystems.

Corals are the best-known reef builders today, but reefs have been built by a wide variety of organisms throughout Earth’s history. One such group was the stromatoporoids, sponge-like organisms that played a major role in reef building during the Paleozoic, particularly during the Silurian and Devonian periods (about 444 to 359 million years ago).

“Stromatoporoids were thought to have become extinct as reef builders after the Late Devonian extinction,” said Yoichi Ezaki, a professor at Osaka Metropolitan University’s Graduate School of Science and lead author of the study.

The Late Devonian Extinction is one of five mass extinctions in Earth’s history. It dramatically affected marine life, causing a decline in the diversity of reef-building organisms. During the Carboniferous Period (about 359 to 299 million years ago), which followed this devastating event, no stromatoporoid reefs were known… until now.

Examining fossils from Carboniferous rocks discovered in the Akiyoshi Limestone Group in southwestern Japan, the research team found laminated skeletons with lamellae, or layered, and pillar-like structures typical of stromatoporoids.

“Contrary to what was thought, our findings in Japan show that stromatoporoids not only survived, but continued to play a key role in reef building during the Carboniferous,” Ezaki said. “We believe this discovery will rewrite the textbooks.”

The Akiyoshi Limestone formed on a seamount in the Panthalassa Ocean during the Mississippian (Early Carboniferous) to Middle Permian periods. Stromatoporoids, along with the organism Chaetetes, thrived on warm, shallow seamounts in the Panthalassa Ocean, benefiting from conditions such as enhanced ocean circulation, upwelling, and nutrient supply, resulting in high carbonate saturation due to ongoing global glaciation.

This suggests that isolated and unique ocean environments like Akiyoshi may have enabled the survival of these resilient organisms.

“The isolated Akiyoshi Seamount may have hosted a unique biological community, potentially forming a ‘Carboniferous Galápagos’ that offers insight into the complex dynamics of ancient marine ecosystems,” Ezaki said.

Intensified global cooling and above-sea-level exposure eventually took their toll on stromatoporoids. However, the continued presence of these reef-building organisms during the late Carboniferous suggests that they adapted to new ecological niches in response to climate change.

The study results highlight the potential resilience of some reef-building organisms in particular environments, providing valuable lessons for current conservation efforts.

“Understanding how stromatoporoids and other organisms have adapted to survive past climatic and environmental upheavals provides crucial insights into how modern reef ecosystems might cope with current and future climate changes,” Ezaki said.