Grande Coupure

The ‘Grande Coupure’ is the ‘great cut’ in Eocene fauna as the climate changed from ‘greenhouse’ to ‘ice-house’ in the blink of a geological eye around 34 million years ago. (The syllables in bold type indicate where the stress should be.)

The Eocene (56–33.9 Ma)
The Eocene was balmy, much warmer than today:
No polar ice, and Europe’s neighbour Asia far away
(They were not then conjoined, although Earth’s magma was a-tossing),
So the Turgai Strait between them offered no terrestrial crossing.

The adapids and leptictids, the little omomyids,
The palaeotheres and pantodonts were really rather shy kids.
Mesonychians, in contrast, were carnivorous and sly,
Who ambushed other creatures who just happened to pass by.

The Oligocene (33.9–23.03 Ma)
But when the Earth’s tectonics saw Antarctica set free
And polar ice-caps locked up thirty metres-worth of sea,
The Turgai Strait fell dry, allowing alien Asian beasts
To thunder into Europe for some Oligocenic feasts:

Entelodonts ate anything – plant fibres, bones and roots;
The hyracodontids’ size had creatures quaking in their boots;
The carnivorous nimravids had teeth like sabres bright;
And ochotonas burrowed for their food, so did all right.

The Grande Coupure
The mammals of the Eocene could simply not compete,
For they had been at home in climates with more heat
And forests that provided them with nourishment and cover;
Until this ‘ice-house’ time arrived and immigrants took over.

As Spencer* might have noted, if he’d been there at the time,
“The fauna that survive are those most fitted to the clime!”.
This mini mass extinction has been called the ‘Grande Coupure’
By Swiss-born Hans Georg Stehlin, whose coining would endure.

*Herbert Spencer’s ‘survival of the fittest’ phrase, in his Principles of Biology (1864), was endorsed by Charles Darwin in the fifth edition of On the origin of Species (1869).

Image of Hans Georg Stehlin:

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