How did the ancient predators get to landlocked Kurgan region, 2,400 kilometres from the nearest ocean?
The fossilised teeth are the most extraordinary find in a graveyard of extinct animals lying on the bed of the Tobol River, on the edge of western Siberia.
They were discovered along with woolly mammoth relics during a dive which was part of an expedition this month led by Sergey Kondrashin, member of the Russian Geographical Society.
Experts are examining 50 shark teeth to ascertain if they are from a known type of the predator.
But what were the shark remnants doing in a freshwater river so far from the ocean? The answer is that this region was once the prehistoric Turgay Sea.
‘Some 29 to 160 million years ago, in the Cenozoic and the Mesozoic eras, the Trans Urals were covered by the ancient Turgay Sea,’ said explorer Kondrashin.
He estimates the shark teeth to be around 32-34 million years old.
‘We are hoping that the scientists will be able to find a species that have not been studied earlier from the teeth of the sharks,’ he said. ‘We will obtain the results in two weeks.’
The teeth were found at a depth of around 3 metres during the dive by members of the Triton diving centre in the fast-flowing Tobol, which took place in an air temperature of minus 24C.
Intriguingly, this depository of ancient bones includes animal remains over an large time span, from tens of millions of years to a few thousand, all in the same stretch of water.
On the same dive, a thigh, tusk and spoke bone of a woolly mammoth was fished out of the water. Found too was part of a skull of an ancient horse, and bones of a bison.
‘All the finds have been passed to the Ural Mineralogy Museum,’ he said. ‘Earlier we managed to find a skull of a a wide-horned bison there, the lower jaw of a mammoth, and the remains of a cave lion and ancient horse.’
He said: ‘This is a unique place, one of a kind in Europe.’ It has ‘an abnormally large aggregation of remains of dead animals’.
Manmade objects have been pulled from the water, too.
‘In January 2015 a fragment of a ceramic jar from the Neolithic Period was discovered on the river’s bottom for the first time,’ he said. ‘It helped to locate a new, previously unknown Neolithic camp of ancient man.’
Now are the shark teeth the only sign of sea life here.
‘The river has eroded away the soft sediments and opened parts of the floor of the ancient sea’ he said. The remains of cramp fish have been found here, for example.