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Eocene animals

There was something of a clearout at the end of the Palaeocene, caused by global warming. It was nothing approaching a mass extinction, on land at least. But the oceans suffered much more. The entire ocean warmed dramatically, changing its chemistry and causing underwater mayhem. As a result, some 40% of the deep ocean micro-organisms died out.

However by the end of the transition recognisably modern animals were beginning to appear.

India hits Asia

The clearout had to do with tectonic changes, as India first hit the underbelly of Asia. You may already know that India has been busily burrowing under Asia ever since, throwing up the Himalayas as it does so. If you ever visit the Himalayan region, it is very obvious that it is much ‘newer’ than many other mountain ranges. Even steep hillsides quite high up, are very soft, very fertile – and being very quickly eroded. And yet there seems to be plenty of good soil left. The mountain ranges that we normally visit are mainly bare rock at these heights.

The collision produced flood basalts, volcanism and methane outpourings, and hence the global warming.

Back to the animals

Even the land climate became pretty hot however, and crocodiles were to be seen swimming off northern Greenland.

The mammals that survived the clearout were pretty primitive. Short thick limbs, clumsy feet and hands, and simple teeth capable only of tearing. But they quickly evolved modern capabilities, like long thin legs, grasping hands and teeth that could chew. They were the direct ancestors of horses, camels, sheep, cows and of course humans.

The collision also allowed animals to migrate to new pastures and possibly out-compete those already there.

Many modern mammals appeared early, including modern rodents, the earliest known horse and modern primates.

In fact the clearout began shortly before the end of the Palaeocene. It resulted in animals becoming very small, the better to cope with the heat. Small animals can lose heat much faster than large animals can.

This is the first horse, Hyracoterium, or Eohippus, “the Dawn Horse”. It first appeared early in the Eocene in the forests of North America. It was the size of a small dog, and had several toes on each foot. (Images copyright Joe Tucciarone.)

Most of the animals seemed to start off as herbivores. And they didn’t stay small for long. By shortly after the beginning of the Eocene (around 55 million years ago) some had grown to 2 metres tall, weighing as much as 5 tons.

The carnivores that came through remained small for a lot longer.

This rhino is Uintatherium. It was around during the late Eocene, in North America and Asia. It was larger than the modern rhino. It was an ancient distant cousin of horses, elephants and, so I’ve read, whales

I’ve read that grass didn’t appear until about 8 million years ago, so these animals must have dined off leaves and other coarse material.

Soon after came animals that were into digging, climbing, running and even flying. Yes, bats had finally appeared.

(I’m indebted to an article by Elisabeth Nadine in Cuss’s ‘Science Notes’ for parts of this.)