By Steven McKenzie
Highlands and Islands reporter, BBC Scotland news website
Evidence of reindeer were found in the caves
They are a window in to the past, according to Alex Scott, an officer with Scottish Natural Heritage (SNH).
The four Bone Caves of Inchnadamph in the north west Highlands, which are protected by SNH, contained a physical record of Scotland's ancient beasts.
Since the late 1800s remains have been excavated from the underground complex.
Last week an almost complete skeleton, recovered over a period of years by cavers, was confirmed as that of a large male brown bear.
It joined a long list of creatures whose remains have been retrieved from the darkness.
They include bones from a polar bear, lemming, arctic fox, reindeer, tundra vole and wolf. Some may have been washed into the caves during Ice Age floods.
The polar bear skull found in 1927, and held in the collections of the National Museum of Scotland in Edinburgh, continues to fascinate scientists.
Believed to the only remains of its kind found in Britain, a sample was taken last year for DNA analysis.
Ireland-based genetics expert Ceiridwen Edwards had hoped to compare the DNA of the animal found in a cave in Scotland with that of modern polar bears.
However, she said there was not enough DNA left in the sample for an analysis to be done.
According to SNH's leaflet on the Bone Caves, one of the most exciting finds was the skull of a Northern lynx dated at about 1,770 years old and also found in 1927.
Puffin were among the finds in the Bone Caves
The discovery makes Inchnadamph the only Northern lynx site in Scotland.
SNH suggests it may have entered the caves through a gap in the roof and died or was dragged there by another animal.
A list compiled in 1996 of finds also includes wildcat, water vole, weasel, stoat, ox, pig and birds such as barnacle goose, puffin, mute swan and several ducks.
The caves were also a burial site and the bones of four people found there have been radiocarbon-dated to being between 4,515 and 4,720 years old.
The recovery of the newly-confirmed brown bear was a painstaking process.
Caving club, Grampian Speleological Group, retrieved the first pieces of bone in 1995.
Cave divers then spent the next 12 years wriggling through narrow spaces and moving soil to unblock entrances in their effort to recover all they could.
Their efforts have paid off with another valuable addition to the record of Scotland's long gone residents.