They were some of the biggest creatures to ever roam the Earth before disappearing more than ten thousand of years ago in a series of mass extinctions.

But it seems the loss of giant animals like mammoths on the land and whales in the oceans has had far more serious implications than has previously been appreciated.

The Earth is suffering from a shortage of dung following the extinction of the planet's megafauna, according to a new study.

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Massive declines in the numbers of large animals on land and in the oceans have resulted in a decline in the movement of key nutrients like phosphorus around the environment. The graphic shows the reductions in phosphorus cycling on the land since the last ice age and in the oceans in the past three centuries

A team of scientists have found there has been a massive decline in the capacity of animals to recycle nutrients in the ecosystem through their droppings since the last Ice Age.

They estimate the capacity of land animals to spread nutrients has fallen to just eight per cent of what it was before the extinction of 150 species of ice age mammals.

SAD DEMISE OF THE MAMMOTHS They were the biggest of the Ice Age giants, roaming the frozen plains of the Northern Hemisphere. But it seems the final days of the woolly mammoth were a sad struggle for survival. Genetic analysis of two woolly mammoth remains show that their population became so small that they had become chronically inbred. Researchers have concluded that the creatures clung on in just a tiny pocket of the Arctic, on an island that appears to have become cut off from the mainland. Advertisement

These included giant sloths, mammoths and woolly rhino which all died out more than 12,000 years ago.

More recently, dramatic declines in the numbers of whales and other marine mammals in the oceans have seen the movement of nutrients drop to a quarter of their previous levels.

Further major drops in the number of fish and seabirds has also led to dramatic declines in the amount of faeces being produced.

Dr Joe Roman, a biologist at the University of Vermont who was a co-author of the study, said: 'This once was a world that had ten times more whales, twenty times more anadromous fish like salmon, double the number of seabirds, and ten times more large herbivores like giant sloths and mastodons and mammoths.

'This broken global cycle may weaken ecosystem health, fisheries and agriculture.'

Woolly mammoths (pictured) played a key role in cycling nutrients on the land during the ice age. With much of the soil locked up in permafrost, their dung provided valuable nutrients to the plant life growing there

Animals were previously thought to play a minor role in the movement of nutrients in the environment with most of it being carried out by weathering of rocks and the actions of microorganisms like bacteria and fungi.

However, the new study shows that animals are a crucial 'distribution pump' as they transport large amounts of faeces to fertilise areas that would otherwise be less productive.

For example the ocean surface waters and interior of continents would be comparatively barren if it were not for a regular supply of dung.

Writing in the journal Proceedings of the National Academy of Sciences, the researchers behind the latest study have found that animals appear to play a far bigger role than previously realised.

They used a set of models to estimate the movement of nutrients in the oceans and across the land and how this changed with the mass extinctions and declining animal populations.

MYSTERY OF WHAT KILLED OFF THE MAMMOTHS There are several leading theories for what killed off the ice age giants like the woolly mammoths. Woolly mammoths are thought to have roamed the Earth from about 200,000 years ago before eventually dying out 10,000 years ago. At this time the planet was undergoing a major change in climate that is thought to have led to the shrinkage of their habitat. Unable to find the food they needed their populations became smaller and increasingly isolated. A study in 2008 estimated that changes in climate as a result of the end of the last glacial period saw their habitat shrink from 3 million square miles to 310,000 square miles. Some researchers have suggested that the spread of forests, which overtook the extensive areas of frozen grassland and tundra where mammoths thrived, led to their extinction. The changes in climate also opened up large parts of the northern hemisphere to humans, allowing groups to spread more widely around North America, Asia and Europe. Many blame overhunting by humans for finally finishing off the dwindling populations of megafauna like mammoths. More recently some scientists have adopted theories that sudden changes in climate, known as the Younger Dyas period, left many large animal species unable to cope. It is thought this period of cooling may have been caused by the collapse of the North American ice sheets into the Atlantic Ocean, leading to the seas cooling dramatically. Others have suggested this was triggered by a large explosion from an asteroid or comet impact that spread debris around the globe. Advertisement

For example, whales are thought to have declined by between 66 per cent and 90 per cent over the past 300 years due to hunting.

There used to be more than 350,000 blue whales – many weighting more than 100 tons - in the oceans around the world but now just a few thousands remain.

These whales tend to feed in the deep ocean and then defecate the sun-lit surface, providing vital nutrients for algae and other plankton.

Prior to commercial hunting of whales, the scientists estimate that whales and other marine mammals annually moved around 375,000 tons phosphorus from the depths to the surface.

They said the figure is now around 82,500 tons - 22 per cent of the former capacity.

On the land, large animals can often carry nutrients from plants in lower areas to higher ground. Their digestion systems speed up the release of nutrients from plant matter.

Overall the scientists calculate that animal-powered fertilisation may have dropped to just six percent of its former capacity.

This is having serious long term impacts on the planet, according to Dr Christopher Doughty, an ecologist at the University of Oxford who led the study.

Large herbivores play a key role in recycling nutrients in areas where the soil is poor. Rhinos, for example, produce large amounts of dung (pictured) from the tough, woody plants they feed on

Blue whales (pictured) used to number more than 350,000 but there are just a few thousand left. Together with other marine mammals they helped to cycle 375,000 tons of phosphorus in the oceans and this figure has now fallen to 23 per cent of its previous value

He said: 'Previously, animals were not thought to play an important role in nutrient movement.

'Phosphorus is a key element in fertilizers and easily accessible phosphate supplies may run out in as little as fifty years.

'Restoring populations of animals to their former bounty could help to recycle phosphorus from the sea to land, increasing global stocks of available phosphorus in the future.'

Writing in the journal they say the role of large animals has perhaps been wrongly overlooked.

They said: 'This notion may be a peculiar world view that comes from living in an age where the number and size of animals have been drastically reduced from their former bounty.'

They added it may be important to restore populations of animals to help ensure nutrients can circulate in the future.

Dr Roman said: 'The typical flow of nutrients is down mountains to the oceans.

'We are looking at ways that nutrients can go in the other direction--and that's largely through foraging animals.

'But recovery is possible and important.