Disappearance of the Malvinoxhosan biota linked to climate change

A new study is shedding light on the mysterious disappearance of certain marine animals at the South Pole between 390 to 385 million years ago. The research illustrates the profound impacts of climate and sea-level changes on marine ecosystems.

Setting the stage 

Gondwana, a vast landmass encompassing parts of modern-day Africa, South America, and Antarctica, was uniquely positioned near the South Pole during the Early-Middle Devonian period. 

Contrary to the icy landscape we associate with Antarctica today, this ancient supercontinent experienced warmer climates and higher sea levels, resulting in the flooding of vast areas of land.

The Malvinoxhosan biota

For nearly two centuries, scientists have been perplexed by the emergence and eventual disappearance of the Malvinoxhosan biota – a group of marine animals that thrived in cooler waters. This group included various types of shellfish, many of which are now extinct. 

“The origin and disappearance of these animals have remained an enigma for nearly two centuries until now,” said study lead author Dr. Cameron Penn-Clarke, an expert in the Evolutionary Studies Institute at the University of the Witwatersrand.

To investigate, the researchers collected and analyzed an extensive amount of fossil data. Using advanced analytical methods, they sifted through layers of ancient rock, each bearing its own unique set of fossils.

Disturbing discovery 

The analysis identified 7 to 8 distinct layers, each progressively showing a decline in marine animal diversity. 

By comparing these layers with ancient environmental data and global temperature records, the researchers found a disturbing correlation: the decline in marine species coincided with fluctuating sea levels and climate changes.

Cooling phase 

After over a decade of intensive research, Dr. Penn-Clarke and his team believe that the Malvinoxhosan biota thrived during a prolonged global cooling phase. 

Cooler conditions fostered circumpolar thermal barriers, such as ocean currents near the poles. This isolation facilitated their specialization. However, as temperatures began to rise, these animals vanished, replaced by marine species better suited to warmer waters.

Alterations in sea levels during this period likely broke natural ocean barriers, allowing equatorial warm waters to permeate the South Pole. Consequently, these warm-water species dominated, signaling the decline of the Malvinoxhosan marine creatures.

Catastrophic breakdown 

The demise of the Malvinoxhosan biota resulted in a catastrophic breakdown of polar ecosystems – a damage that was irreversible. 

“This suggests a complete collapse in the functioning of polar environments and ecosystems to the point that they could never recover,” said Dr. Penn-Clarke. 

“It’s a 390-million-year-old murder mystery. We now know that the combined effects of changes in sea-level and temperature were the most likely ‘smoking gun’ behind this extinction event.”

A global phenomenon?

While this extinction event may have corresponded with known extinction events during the Early-Middle Devonian, researchers do not have adequate age inferences.  

“This research is important when we consider the biodiversity crisis we are facing in the present day,” said Dr. Penn-Clarke. “It demonstrates the sensitivity of polar environments and ecosystems to changes in sea level and temperature. Any changes that occur are, unfortunately, permanent.”

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