Fauna - Sima de los Huesos

Por Nuria García

Surrounded by darkness, ancestors of the cave bears (`Ursus deningeri´) entered the Cueva Mayor looking for a secluded but convenient corner to hibernate, waiting for the fruits the spring will bring. It is cold outside. A bear and her cub find the perfect spot inside the Sala de los Ciclopes, and there they make themselves comfortable. Another young adult, however, prowls around in his search of the cave and, attracted by the pleasant smell of carrion, reaches the mouth of a sinkhole some 13 meters deep: he is facing the Sima de los Huesos. The odor coming from the dark bottom is more intense there, putting all his instincts on alert, which are more focused now on the climb down to the source of such delicacies. The rough descent ends with a hard fall, but despite being injured, he gets the desired taste of rotting meat from some of the carcasses accumulated there. Sadly, there is no way out but the vertical shaft, now impossible to ascend. The intrepid young bear has fallen in a natural death trap, and his lifeless remains will feed the constant string of bears, foxes, weasels, and many other carnivores that subsequently fall in. The Sima de los Huesos also contains human remains which represent an early mortuary practice and their presence can be explained differently from that of the carnivores. This combination of taxa, humans and carnivores with no evidence of herbivores, is completely unknown for a place considered to be a home or shelter for humans. This large accumulation, biased in favor of carnivores, indicates that they came here attracted by a good reason: food. Almost 180 bears, one wolf, 25 foxes, three lions, two lynxes, one wild cat, three weasels, one beech marten, three European polecats, and one European badger accumulated over the years in the Sima around half a million years ago. The preNeandertal human bodies were deposited at the Sima for different reasons.

Bears, Paws

Among the fossils extracted from the upper sediments at Sima de los Huesos, there is no evidence of lithic manufacture or herbivores: something very unusual in deposits of the same time period. This accumulation was composed exclusively of bears (more than 150) and other carnivores: three lions, twenty four foxes, some wolves, lynx, and mustelids. The research done by Trinidad Torres had established the identity of the bear in question as `Ursus deningeri´, the ancestor of the formidable cave bear typical of the Upper Pleistocene. Its size was superior to that of a great European brown bear, and it was specialized as an omnivore, with less preference for meat than extant bears.

The Sala de las Oseras is closed due to a collapse inside the cave, in a point that according to the maps, it is located a couple of meters away from the roof of the Sima. This cavity is named after the presence of hibernation beds, a sort of nest made on the floor clay where these animals spend the winter. Some cracks in the cave wall are filled with clay and still preserve paw prints made by the bears’ claws, so fresh that they seem recent. A small excavation in the Sala de las Oseras discovered dozens of almost intact bones from `Ursus deningeri´. There were remains of every kind: juvenile and adult bears with cubs accumulated along the walls. It was here where the last of their species moved the bones aside to make their own beds.

In contrast, the bears whose remains were founded at the Sima de los Huesos didn’t hibernate there. This part of the cave has functioned for a long time as a natural trap. Its mouth is tight and difficult to pass through, and the 13 meter abyss opens without warning in a corner of the cave apparently ideal for sleeping for several months. If a bear looking for a place for its winter’s nap gets distracted, it might fall in. This was what happened to 160 of them over several millennia. Many of them didn’t die instantly. Wounded and trapped in a pit with no way out, their agony would have been slow, and their survival instinct led them to scavenge the remains of other equally unfortunate fellow bears that had fallen previously, moving and crushing the bones in the process, until in the end, they died. When this happened, the flesh did not last long (just months) before disappearing, and their skeleton remained in the same position as at the moment of death until some other unfortunate individual, sometimes a mother with her cubs, fell over them, little by little forming an ossuary.

Carnivores

At least on several occasions these rotting carcasses attracted other carnivores, as well as other bears to a certain death. Three lions, almost certainly a male, female, and a juvenile, must have followed their nose to satisfy their hunger, ended up dying at the bottom of the shaft. No less than 24 foxes followed the same fate, as well as a couple of lynx, a wild cat, three weasels, two marten, and one wolf. The Sima had become a sophisticated bait trap.