Dinner at the Denisovans: Blue Sheep

Once upon a time, there were multiple species of humans. Discovered thanks to incidental genetic analysis of a single ancient finger-bone found in a cave in Siberia, they turned out to be a "sister species" of the Neanderthals. Meaning Neanderthals and Denisovans had a common ancestor. While the Neanderthals emerged in the West, in Europe and the southern Levant, the Denisovans occupied the East. As Homo sapiens emerged in Africa and exited that continent, we met both Neanderthals and Denisovans, and interbred with both.

Genetic research implies that the Denisovans lasted longer than any other alternative human we know of, dying out in Southeast Asia only about 15,000 years ago.

The burning question of the day is what they ate before they did so.

The answer was a theoretical "probably what other hominins did" – and actually that isn't wrong, it can now be said, based on finds in a Buddhist sanctuary inside Tibet's Baishiya Karst Cave.

Baishiya is the second place in the world where Denisovan remains have now been identified. The first had been in Siberia's Denisova Cave.

Open gallery view The original Denisovan finger-bone found in Denisova Cave in 2008. Credit: Thilo Parg

The dining habits of the Denisovans have been deduced based on the identification of animal bones inside the prehistoric site of Baishiya Karst Cave on the Tibetan Plateau. The identification of a Denisovan rib among animals bones was reported in Nature on Wednesday.

The rib dates to between 48,000 and 32,000 years ago. This Denisovan was alive when modern humans were spreading across Eurasia, reports the team headed by Frido Welker of Denmark's University of Copenhagen, Dongju Zhang from China's Lanzhou University and Fahu Chen from the Institute of Tibetan Plateau Research with others. The rib was broken during the excavation, the archaeologists admit.

They note that separate work detected Denisovan DNA in the cave soil. However, finding the rib is like finding gold.

To be clear, back in 1980 a monk found a jawbone in Baishiya Karst Cave that was, decades later, identified as Denisovan and was much older – about 167,000 years. Which means the Denisovans were in the cave, consecutively or otherwise, for a cool 120,000 years, from at least 167,000 years ago to around 40,000 years ago. They could theoretically have lived there even longer.

Emphasis on cool: Baishiya is 10,760 feet (3,280 meters) above sea level; it is nippy and the air is relatively oxygen-poor. The rib therefore is the second Denisovan bone to be found there.

The discovery of Denisovan bones in Siberia and the Himalayas, and the perpetuation of the species in the jungles of Southeast Asia based on genetic evidence, suggests the species was highly adaptable. They weathered two ice ages and the interglacial period, co-author Welker has pointed out.

Open gallery view The original Denisovan finger-bone. Credit: Dongju Zhang

The team analyzed more than 2,500 bones extracted at Baishiya, high in the Tibetan mountains. Truth is that most of the bones were in such terrible shape that their source couldn't be identified beyond not-plant. The team therefore tapped a technique of identification by protein analysis called "zooarchaeology by mass spectrometry," or ZooMS.

Our DNA is unique at the level of the species – no species other than human will have human DNA – and at the level of the individual: no other human will have the same DNA as you. Not even your identical twin.

We have DNA codes for protein such as collagen. Now, no species other than human will have human-type collagen. And no species other than blue sheep will have blue sheep-type collagen. You see where this is going?

So, who was in the cave? If one finds prehistoric remains from wild animals who do not live in caves, chances are the Denisovans brought them there.

Blue sheep (Pseudois nayaur) are the only species in their genus, Pseudois. They are pretty and both sexes have horns. The males have bigger ones. Blue sheep don't live in caves but do live throughout the Himalayas, including mountain areas of China, Tibet, Pakistan and India. They look like goats (as true wild sheep do), sport horns and, like the Russian blue cat, the animal isn't turquoise or aquamarine but gray with a sort of periwinkle sheen.

The blue sheep is also characterized by a white tummy and was the dominant animal found in Baishiya Karst Cave, as well as remains of wild yaks, wild horses, woolly rhinoceroses and small animals too.

Open gallery view A female blue sheep, with smaller horns, in North Sikkim, India. Credit: Dibyendu Ash

Visit from a hyena

Denisovans basically ate the usual hominin fare: whatever they could catch – preferably big animals when there were any, and smaller animals when they had to.

The team also identified some bones of carnivores such as the hyena, which may have been eaten or also inhabited the cave, as well as remains of small animals such as marmots and birds. Cut marks were also identified on small animal bones extracted from the cave.

The team claims they also detected evidence of pelt processing – were the Denisovans making clothing to help against the cold? We can only surmise.

In short, possibly the hyena aside, these animals didn't stagger into the cave for their eternal sleep.

"The high proportion of anthropogenic modifications on the bone surfaces suggests that Denisovans were the primary agent of faunal accumulation," the team writes. Why would sheep dominate? Possibly because bigger animals had likely gone extinct, or were going there.

What can be concluded? For one thing, the area of the cave was not forested, which blue sheep can't stand, but one characterized by grassy slopes. Caprines like a nice grassy slope, though they will eat leaves from the scrubby bushes of the region if they have to. The cave may have been quite stable in conditions during glacial and interglacial periods alike, the team suggests.

Long bones from big animals had traces of marrow extraction, which has been widely observed at sites of early humans and their predecessors. The signs are percussion marks on the bones of front and hind legs of the sheep, aurochs, horses and woolly rhinos – and the Himalayan marmot.

Open gallery view A Denisovan molar found in Denisova Cave, Siberia. Credit: Thilo Parg

Separate work by Israeli scientists suggests that fatty, nutritious bone marrow for hominins wasn't a luxury: it was a must for a carnivorous hominin that couldn't gain too many calories from meat or they'd get nitrogen poisoning. It stands to reason that Denisovans would also crave it.

So what have we? Denisovans seem to have been a tough species that persisted through weather extremes, laughed in the face of oxygen depletion, ate whatever fell into their traps or onto their spears, though if it was a blue sheep this was nice. Possibly the blue sheep became the dinner du jour as the bigger animals were wiped out. Possibly the Denisovans could tailor clothing from the hides of the bigger herbivores to help beat the cold and wind. And after all that, like the woolly rhino, the mammoth and most of their favorite meals, they went extinct too.

We do not know why, and this study sheds no light on the conundrum. But it wasn't because blue sheep went extinct too. They never did, and that's probably because they live in very inaccessible places where we can't catch them like the Denisovans did.