11 May 2010


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‘Animal play is experimenting in a relaxed field.’ 
Robert Fagen

Around 60 million years ago  (or Once upon a time . . .) life was beginning to recover from Earth’s Fifth Major Mass Extinction. With no more seemingly insatiable browsers, flowering shrubs and trees were forming thriving and diversifying forests on each continent. And all the recycled dinosaur bodies in the soil were also a great help.

Many plant and animal remains had also found their way into huge depressions on continental shelves and ocean floors. Some would be compressed into new carbon deposits, and then some of that would be trapped below impenetrable rock by violent movements in Earth’s crust. Over millions of years this would become natural gas and petroleum, literally ‘stone oil’, the most significant and aptly named fossil-fuel today. Based on the contribution of dinosaur remains to the mix a few environmentalists call it ‘dinosaur-blood’ to remind themselves and us of its age and unrenewability.

Meanwhile most mammal species were small and competing fiercely for space. Many were losing the struggle and becoming extinct but the successful ones were diversifying to fill the ecological niches left by various dinosaur species. The males were still solitary, and the females lived with their young only until they could look after themselves. And all still had a distinct smell of their own, and a strong sense of the smell of other mammals.

Offspring stayed close to their mothers, practising through play the skills needed for browsing, mating, escaping and/or fighting. Those that didn’t learn were more likely to die without reproducing. So mammals were establishing an extremely significant way of living as far as human evolution is concerned: the development of life-skills through play. Simply put, their programming included an urge for playful learning, and a part of the mammalian brain called the hippocampus was developing, able to store memories of what they learnt.

But a few were beginning to grow larger in the diversifying forests. The first ones to do so were browsers, with one eye on each side of their head to keep watch for danger as they ate – they needed a lot of food. Some of them had developed long trim legs designed for escape from predators: the forerunners of horses, giraffes, camels and buffalo. And some had developed shorter thick legs designed for standing and fighting them: the forerunners of elephants and rhinoceros.

Their predators included creodonts, the fore-runners of today’s carnivorous mammals, although they were still small, and hadn’t yet diverged into distinct dog and cat families. But the most dangerous might have been huge flightless birds, like Diatryma, in North America. They were 2 metres tall, with strong kicking legs, a skull almost as big as a modern horse, and a hooked beak that capable of killing their prey with one snap.. They apparently preyed on small browsers like Hyracotherium, an ancestor of horses.

In the trees were ancestral primates, eating young treetop leaves and shoots, as well as seeds and fruit when they could find them. They were early members of the order of primates, diverging from other mammals because of their different life-style.

They had long free-moving limbs and grasping feet, more like hands, but at this stage they were slow-moving and slow-thinking., However the offspring had to observe and practise complex new skills relating to their treetop life-style. These included finding and reaching for food high in the trees, and avoiding their predators on the ground by moving from branch to branch. Their learning must have involved a lot of risky trial and error, challenging the hippocampus to remember more and more.

Since well-focused eyesight was more useful in the trees than a keen sense of smell was, over generations their sense of smell would diminish and their sight improve. And, like carnivores, they were developing eyes that faced to the front. One early primate was the Adapis, 40 cm long.

Eventually huge plant-eaters were browsing on high-growing leaves much as giant dinosaur plant-eaters had done. In Asia they included Indricotherium, a hornless relative of today’s rhinoceros, and the largest land-mammal ever. But it weighed only up to 20 tons, and stood only 6 metres high at the shoulder.

By now larger mammal carnivores had evolved, including sabre-tooth cats. They needed food less often than their prey did, but, although there was plenty of it around, a large mammal took some catching.

It seems that each cat had to stay undercover to ambush a large browser, creep almost underneath it as it fed, inflict a fatal ripping wound to its huge belly or throat with its sabre-like incisor teeth, get out from under, and then wait until it fell down before feeding on it. But it did not need to make another kill for some time.

Around this time bats emerged, and the Pakicetus mammals returned to the water. They were the size of otters but their descendants include the Blue Whale. With females up to 30 metres long and 150 tonnes in weight, they are larger than any dinosaur yet discovered.

(At the other end of the scale another long-living descendant of primitive spiders evolved in Australian rainforests, living in much the same way as the older, more timid Trapdoor Spiders. We call them Funnel-web Spiders, although the webs in their burrows, where they huddle during the day, are more like long socks.

(Several spiders are known to be among the most dangerous creatures on Earth today, and the notorious Sydney Funnel-web Spider, Atrax robustus, is one of them. They are very unusual among spiders because it is the male that causes human deaths. During summer and early autumn, on the New South Wales central coast and mountains, they leave their burrows to go courting. They are so pumped up that they attack in response to any perceived threat, regardless of its size. And so humans do not intimidate them. When on a death-defying mating expedition one of their males can kill a human who gets in his way.

Their cousins, the Blue Mountains Funnel-webs, are not so dangerous to humans because they do not live in built-up areas.

Around this time perching songbirds, or passerines, emerged in Australia, and from there began to radiate out across the Earth. The Australian lyre-bird is their closest relative today.

Meanwhile, as the Atlantic Ocean expanded between Eurasia’s west coast and the Americas, the rim of the Pacific Ocean was disappearing under Eurasia’s east coast (forming the volcanic islands of Japan) and under South America (forming the Andes). India and Eurasia were also being pressed together, progressively pushing up the soaring triple range of the Himalayas (although the vast Tibetan plateau that has such an enormous effect on Earth’s climate may have already been raised in previous tectonic movement). And Africa was coming ever closer to Eurasia.

As Africa’s and Eurasia’s continental shelves were thrust together huge petroleum deposits were trapped beneath areas that were beginning to dry out, and the European Alps and several Middle Eastern mountain ranges began to rise. Once today’s Morocco came up against southern Spain the deepest part of the enclosed Mediterranean Basin would be in turn sea and saltpan as the Atlantic Ocean rose and fell with Earth’s temperatures. Then 5 million years ago a surge of Atlantic water gouged out the Strait of Gibraltar 300 metres deep, and since that time this deepest area has been the Mediterranean Sea.

Today the Pacific Ocean’s submergence under Japan and the Americas still causes upheaval, and so do India and Africa as they keep moving north against Eurasia. In the future today’s Alps will be a much higher barrier than they are today.

(In this period Australia finally split away from Antarctica and moved north, with New Guinea still attached. But the islands of New Zealand were now being pushed up, and the Tasman Sea was forming between Australia and New Zealand. As it became isolated New Zealand retained no mammals of any kind. Without them a reptile and three flightless birds would thrive for millions of years: the tuatara, and the moa, kakapo and kiwi.

(Australia had monotremes, marsupials and placentals at this stage. So why are there no placentals here today, apart from bats that flew in later?

(The monotreme ancestors of the echidna and the platypus could only survive by filling an ecological niche that had no marsupial or placental competitors. But a marsupial mother would have an advantage over a placental mother in the hard times that became the norm in inland Australia. She could keep an embryo dormant in her womb, or allow a foetus in the pouch to die as her special foetal milk dried up. By contrast a mother that fed her infant through a placenta was likely to die with it.

(So marsupials prevailed because they were fitter for their Australian environment.)

Marsupials in South America weren’t so lucky. As their homeland moved north, volcanic eruptions would lift Central America out of the ocean, and before long the vast majority would be displaced by placentals that had crossed this new bridge. Among those to die out first would be the carnivores, like the marsupial sabre-tooth, Thylacosmilus. Those that remain today, like the opossum family, have survived so far by staying small, maintaining a nocturnal life-style - and eating with what some unkindly call a vacuum-cleaner approach.

But back in our story, a severe climate change was beginning. For billions of years Earth’s inclination to the Sun had varied as a result of its landmasses moving, joining and separating. This was because the Moon’s gravity pulled most strongly on the parts of Earth covered by an ocean. Now that a seaway (what we call the Antarctic Ocean) had opened up around Antarctica, there would be a change in the circulation of water and winds around every continent, and also a slight change in our planet’s tilt.

Over the next few million years a cold circumpolar current built up, leading to a huge deepening blanket of ice on the new continent and the extinction of plants and animals there. And then a very cold period followed across Earth for 10 million years. 

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