Jurassic shift: Changing the rules of evolution

For more than 150 years, scientists have debated whether the success of organisms is mainly down to environmental factors such as climate change or whether — as advocated by Charles Darwin — interaction between species has a significantly more important role to play. A British-German study involving palaeobiologist Prof. Dr. Wolfgang Kießling from Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) has now shown that the influence of environmental factors was considerably greater at the early stages of the evolution of animal life before becoming significantly less important 170 million years ago.

Satellite image of an algal bloom of Emiliana huxleyi off the south west coast of England.
The calcified shells colour the water milky white [Credit: NASA]

The team investigated the fossil record of marine life over the past 400 million years. The ecological success of marine organisms, measured by the proliferation of the various species, was strongly dependent on suitable chemical and climate conditions until roughly the middle of the Jurassic period. During the Jurassic period, approximately 170 million years ago, the situation changed. Since then, it would appear that biological interactions have played the major role.
Why this sudden change and why at this particular time? ‘The answer probably lies with microscopic organisms, or plankton. The rise of planktonic algae with a calcified shell began in the Jurassic period. Gigantic quantities of these calcifying algae are still drifting in the ocean today and form calciferous sediment on the ocean floor after they die. The calcite helps to balance out acid. This facilitates the formation of calcified shells and allows organisms to use their energy differently,’ explains Professor Wolfgang Kießling.

Another explanation can be found in the organisms’ metabolism itself. On average, evolution made animals more and more active. Increased activity goes hand in hand with an improved physiological buffer. A coral is more at the mercy of the environment than a snail, for example.

A greater level of activity also means, however, an increased need for oxygen. Again, the algae appear to have had a crucial impact: Calcifying plankton have a higher sinking velocity which allows them to reach greater depths before they are eventually eaten by other organisms consuming oxygen. This increases the oxygenation of shallow waters. 170 million years ago, small algae had a genuinely revolutionary effect on the rules of the game for evolution, which still apply today.

The study is published in Nature Geoscience.

Source: University of Erlangen-Nuremberg [July 08, 2019]

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