Horses, Grasses, and Climate

Museum für Naturkunde Berlin

The development of horses, grassland ecosystems and climate are closely correlated

The evolution of the horse family over the last 50 million years is closely related to the spread of grassland ecosystems.

The ancestors of the horses, donkeys, or zebras we know today were small animals, not much larger than a dachshund.

They lived in rainforests – structurally similar to the forest shown here. Not a good habitat for today's large horses!

Best known in Germany is the Eurohippus shown here, discovered in the bituminous shale pit of Messel. It was fossilized around 48 million years ago, together with many other species, in the muddy bottom sediments of a deep lake.

Tip
If you are near Frankfurt or Darmstadt in Germany, we recommend that you visit the Besucherzentrum des UNESCO Weltnaturerbes Grube Messel, Roßdörfer Straße 108, 64409 Messel (http://www.grube-messel.de). Also you may want to view a Google expedition on Messel prepared by the Senckenberg Museum für Naturkunde.
Grass
Horses mostly eat grass. The first true grasses in the course of evolution date back to the time of the dinosaurs. However, they grew mainly in forests and swampy areas.
Grass Ecosystems
Prairies, savannas and other large-scale grass ecosystems spread globally only over the last 30 million years. An example of such an ecosystem in Africa is shown here. – At the same time, horses and other grazers began to change their diet, eating more and more grass. Some species also grew in size to meet the challenges of the open landscape that offered little cover to hide from predators.
Climate
A close correlation exists between these processes and global climate changes. Since the late Eocene (about 35 million years ago) decreasing global atmospheric CO₂ levels resulted in an increasingly cold, dry climate.  As a result of a more effective photosynthetic pathway, grasses are better adapted to lower CO₂ content in the atmosphere and can more easily live in drier habitats than many other plants. This favored the spread of grassland ecosystems. Image: (Gjon Mili, TimeLIFE Photo Collection)

Several processes working together have contributed to the reduction of atmospheric CO₂ since the Eocene and the resulting phase of cooler temperatures. An important factor is increased ocean plankton growth. As these plankton cells died, they settled to the ocean bottom and were buried – along with their carbon – in deep-sea sediments. These sediments have held the carbon ever since. The resulting long-term loss of carbon from the system reduced the greenhouse effect of the atmosphere. In turn, this reduced average global temperatures and set the stage for the later development of the ice ages. Today, the reverse process is happening: The burning of fossil fuels like natural gas, mineral oil, or coal releases carbon that had been held in the earth for 100s of millions of years. The result is a sharp increase of CO₂ and global temperatures.

(Image: A modern phytoplankton species, Asterolampra marylandica, J.R. Dolan & G. Hagedorn, CC BY-SA 3.0)

On the long journey from the tiny Eurohippus ...

... to the majestic horses of our human history, climate and grassland ecosystems were important travel companions!

(Horse sculpture from Halikarnassos, 350 B.C., British Museum)

Credits: Story

Images: Antje Dittmann, Carola Radke (Museum für Naturkunde Berlin), Google Streetview, Lothar Rössling, British Museum, J.R. Dolan
Text: Gregor Hagedorn, Faysal Bibi, David Lazarus (Museum für Naturkunde Berlin)

For more information on Messel pit we highly recommend the Online Exhibition of our close partner Senckenberg:
UNESCO World Heritage Messel Pit Fossil Site – An ecosystem in Hesse 48 million years ago.

© www.naturkundemuseum.berlin

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
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