Sea-Level and Climate Fluctuations Altered the Marine Ecosystems at the South Pole 390-385 Million Years Ago

A new study has solved a 390-million-year-old mystery of how a group of ancient marine animals near the South Pole went extinct.

The study, led by Dr. Cameron Penn-Clarke from the University of the Witwatersrand, found that these animals, known as the Malvinoxhosan biota, were killed by a combination of climate change and sea-level rise.

The study also revealed how these animals evolved and adapted to the polar environment, and how their extinction affected the biodiversity of the region.

The study was published in Earth-Science Reviews.

The mystery of the Malvinoxhosan biota

(Photo : Monaco Palace via Getty Images)

The Malvinoxhosan biota were a group of marine animals that lived near the South Pole during the Early-Middle Devonian period, about 390 to 385 million years ago.

They included various types of shellfish, such as brachiopods, trilobites, and ophiuroids, many of which are now extinct.

These animals thrived in cooler waters and formed a unique bioregion that was isolated from the rest of the world by ocean currents.

The origin and disappearance of these animals have remained an enigma for nearly two centuries until now.

A new study by Dr. Cameron Penn-Clarke from the University of the Witwatersrand and his colleagues has shed light on how these animals evolved and went extinct in response to changes in sea-level and climate. 

Dr. Penn-Clarke said that this research was around 12-15 years in the making, and it was not an easy journey. He said that he was only able to overcome all the different challenges through dogged persistence and perseverance.

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The rise and fall of the polar marine ecosystems

The researchers collected and analyzed a vast amount of fossil data from South Africa, which was part of a large landmass called Gondwana that included parts of today's Africa, South America, and Antarctica.

Gondwana was located near the South Pole during the Early-Middle Devonian period, but unlike today's icy conditions, the climate was warmer, and the sea levels were higher, flooding most of the land.

The researchers used advanced data analysis techniques to sort through layers of ancient rock based on the types of fossils found in them.

They then identified at least 7 to 8 distinct layers, each showing fewer and fewer types of marine animals over time.

These findings were then compared with how the environment and sea levels have changed, as well as with global temperature records from that ancient period.

They found that these marine animals went through several phases of declining numbers of different species, which correlated with changes in sea levels and climate.

Their research suggests that the Malvinoxhosan biota survived during a long period of global cooling. Dr. Penn-Clarke explained that cooler conditions allowed for the creation of circumpolar thermal barriers-essentially, ocean currents near the poles-that isolated these animals and led to their specialization.

As the climate warmed up again, these animals disappeared. They were replaced by more generalist marine species that are well-adapted to warmer waters.

Shifts in sea levels during the Early-Middle Devonian period probably disrupted natural ocean barriers that had kept waters cooler at the South Pole.

This allowed warmer waters from regions closer to the equator to flow in, setting the stage for marine animals that thrive in warmer conditions to move into these areas.

The extinction of the Malvinoxhosan biota led to a complete collapse in polar ecosystems, as biodiversity in these regions never recovered.

Dr. Penn-Clarke likened this research to playing a game of Cluedo. He said that it was a 390-million-year-old murder mystery.

He said that they now know that the combined effects of changes in sea level and temperature were the most likely 'smoking gun' behind this extinction event.

Furthermore, he said that this research demonstrates the sensitivity of polar environments and ecosystems to changes in sea level and temperature.

He concluded by saying that this research has important implications for understanding how modern polar ecosystems may respond to ongoing climate change and sea-level rise.

This research shows that polar ecosystems are fragile and vulnerable to environmental perturbations and that once they are lost, they may never recover.

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