Big 5 Mass Extinctions (2/5)

Upper Devonian, Kellwasser Event (~360 Ma)

• ~ 40% of species died
• first forests were formed
• new types of reefs are made of stromatopores
• causes: global anoxic conditions, regression, plate tectonics
• Variscan Orogen was formed, Rheiic Ocean closed

The Kellwasser Event took place in Devonian and lasted for about 3 Ma. The name Kellwasser origins from a valley in mid-germany. Gray layers of limestones from the Kellwasser valley document this event of mass extinction.

But what happened around 360 Ma ago? What killed so many species?

At first there was yet again a formation of an orogen, the Variscan Orogen which resulted from the closure of the Rheiic Ocean. The Devonian system brought out new forms of life such as seed plants and furthermore forests. It’s also called the time of fishes.

As you might have learnt in the post about the first of our Big 5 Events in Upper Ordovician, a drop of sea level affects species that live in shelf area the most. In that time, stromatopores and corals dominated the palaeonzoic reefs and for the first time, those areas reached an expansion of up to 6 by 100 m, which has never been there before. Compared to today’s sea life, such kind of dominance in a reef is extraordinary. But not only regression stressed the organisms, there was also a global anoxic condition in sea water. The so called “warm saline deep water” was pushed towards the shelfs, and that stress led to an exctinction of many species for a lack of O₂.

Ecosystems had to resettle other, new environments, organisms are “going upstream” and this movement plays an important role in the evolution of amphibians. Since water isn’t a implicitness anymore*, those vertebrates need to cope with new conditions. They need to be independent from water. The evolution of amphibians begins with a species called Ichtyostega.

_{*A high range of ∂¹³C ratios indicate a volatile climate condition, with the effect of a frequent change of greenhouse and icehouse.}

See all Events.