At www.vice.com/en_uk/article/j5wnx7/ancient-bone-crushing-hyena-roamed-the… … hyenas, during the Ice Age, lived between Mexico and the Yukon, in the far north. Ice Age hyenas are said to have lived in the Arcitc – the assumption being that the geoid of the Earth has remained unchanged. Hyena fossils are sometimes found in the UK (in cave deposits for example) but the Yukon example involved three teeth found back in the 19760s. They have since come under scrutiny and were found to be the teeth of hyena leading to the declaration that hyenas lived in the Arctic – which is akin to saying elephants lived in the Arctic (the mammoths). Why these hyenas disappeared is also a mystery as they fill a unique niche in the natural world, being able to dispose of the big bits of large animals (after death). The teeth were found amongst 50,000 fossil bones and remains in the Old Crow River region of the Yukon (and are defined as a riverine deposit). How a river running downstream managed to shift fossils upstream is something of a dilemma – unless they originated on mountains and high ground (whic presumably is the assumption). Dating them absolutely is something of a problem as the sediments they were within are no old than 1.4 million years ago – which means they could be as young as the end of the last Ice Age. They could also date to any of the Pleistocene glaciations – or interglacials.
Old Crow Basin is the largest of four interior lowland areas within northern Yukon territory. Sediments washed into the basin built up deep deposits that buried and preserved the remains of animals and plants creating a rich fossil record locked up in the permafrost and spanning, it is thought, a million years. However, the fact the deposit consists of sediments and animal remains, which must have been buried quickly in order to have been preserved, suggests an eruption of the Arctic Ocean inland (drowning the lowland areas and dumping the animals). This could of course have occurred in a semi-uniformitarian manner as earthquakes and volcanoes are a feature of Alaska, and presumably of the Yukon. They are not unusual. However, the deposit could also have been made by a bigger event, or catastrophe – or even a series of lesser catastrophes. In that context the deposit is catastrophic in nature and accounts for the high level of preservation. The deposits also bear some similarities with the muck deposits on the Pacific side of Alaska and the Yukon.
See for example https://en.wikipedia.org/wiki/Old_Crow_Flats … which provides lots of links.
The four basins have rivers that ran into the Mackenzie river delta system. Changes in the hydrology occurred during the last Ice Age (or the Late Glacial Maximum) diverting these rivers opening to the Arctic Ocean somewhat further to the west. This could have occurred if Alaska and a tract of Yukon were unglaciated but glaciation occurred towards the east. That is a possibility. However, the diversion of the Porcupine River affected the drainage of Old Crow, Bluefish and Bell basins, the Porcupine river creating a deep cutting into the muck deposit, and this applies also to the Old Crow. The newly created bluffs, or cliffs created by water (the river or a flash flood or intrusion by the ocean), have proved to be a rich source of fossils. They are 30m high in places and huge numbers of fossils have since eroded from the cliffs (as a result of frost and spring thaw, and heavy precipitation on occasion). It is among these fossils that the hyeana teeth were found.
The fossils include mammoth, giant beavers, ground sloths, camels, horses, bison, bears, lions, skunks – many of which do not occur in the Arctic today. Some of the mammoth bones have been C14 dated between 25,000 and 40,000 years ago, precisely contiguous with a Late Glacial Maximum upheaval. However, it is also clear that the cliff deposits could be much older than the Late Glacial Maximum – and it is estimated the muck deposits further south could have been laid down, added to, and added to on several occasions, and that is the likely scenario here at Old Crow. Fossils are also found on the modern river banks and on bars (silt or sand islands) in those rivers. One is left wondering how many fossils remain hidden in the permafrost of the far north, where there is no river to cut through them. The same might be true of Siberia and points west.