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Chauvet´s_cave_horses

Prehistoric animals often feel only slightly more real than mythical beasts. Known only from bones darkened by time and flattened to rocks, it’s hard to imagine them as living animals. How did the animal move? How it behaved? What color was it?

During the last decade or two, more and more wonderfully preserved fossils of dinosaurs have been found. Researchers have even learned to look for traces of their coloration in life. But still, the most vivid window to life in the past is that presented by the megafauna of steppe grasslands, which was skillfully immortalized by our own ancestors as cave paintings. (Painting from Chauvet Cave, France, photographed by Thomas T.)

Not only do cave painting record what the animals looked like, they also show what Ice Age people felt about them. Take the Pech Merle mammoth for example. It’s not just a picture of a hairy elephant. It’s huge, monstrous and obviously scary. Things that the painters thought as unimportant, such as eyes or hooves, are often painted with careless swipes or left off, while the feeling of mass and movement is so strong it still feels the animal could at any moment step out of the cave wall.

Study of cave paintings has started to merge with the information gathered from frozen carcasses preserved by Arctic permafrost and modern DNA research. Together, these fields have painted a literally colourful picture of a lost world teeming with wildlife. Ancient men lived alongside black and red mammoths, great elks with humps, horses of many colours and red-headed neanderthals.

shelk irish elk megaloceros cave painting maija karala

Misleadingly named the Irish elk, Megaloceros giganteus is not Irish nor technically an elk either. It is, however, one of the first animals whose depiction in cave art affected the scientific consensus on how it looked like in life. The Irish elk is a popular subject of cave art on many caves around Europe. In 1974, Stephen Jay Gould noted that the paintings of Irish elks regularly have dark, long-haired humps on their shoulders, often paired with a dark stripe down the side of the animal. It seems quite unlikely that artists living far apart in both space and time would have come up with such an addition if it wasn’t really there.

pech_merle_cave_painting

For a long time, it has been unclear exactly how naturalistic cave paintings are. They have been interpreted as shamanistic works, possibly presenting mythical beasts and painted in a trance. One of the best known examples of mythical creatures are these spotted horses on a smooth rock wall in Pech Merle cave, France (Public Domain from Wikipedia). The coloration of non-spotted horses also varies from light brown to grey and almost black. Obviously real wild animals don’t come in such palette of colors, right?

Not so fast. In a paper published in 2011, a research group confirmed there actually were many colors of wild horses in prehistoric Europe. The group collected bone samples of 31 horses from different sides of Europe, extracted DNA from them and managed to sequence parts responsible for color variation in modern horses.

Most of the horses, 18 of the 31, that is, turned out to be bay. That is, brown with dark manes, tails and legs. Seven of the horses, though, had two recessive a alleles in a locus called agouti. This lets the black pigment affect the whole body instead of just their extremities and makes a fully black horse.

These animals probably weren’t all brown and black, though. At least all living wild equids and many horse breeds considered primitive carry the dun gene, which dilutes both brown and black pigments. The gene has not yet been located in the horse genome, which unfortunately prevented the researchers from checking it.

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Effects of the dun gene include lightening of pigments in the horse’s torso: black turns to dark grey and brown to light brown, making coat colours known as grullo and bay dun. Manes, tails and legs stay dark, though. These horses also often have what are called “primitive markings”: a black dorsal line, dark stripes on legs and shoulders and light guard hairs on the edges of the mane and tail (bay dun Przewalski horses by Ancalagon from Wikimedia Commons). Interestingly, the grey and light brown horses depicted in cave art match these genotypes pretty exactly.

One of the bay horses also carried a single copy of a recessive allele known as e. As a single copy, it had no effect on the appearance of the horse, but if an individual has two copies of this allele, it eliminates all black pigments and makes a horse with brown or blonde mane, tail and legs, a coat color known as chestnut.

This already makes at least three kinds of horses. But wait, that only included 25 from total of 31 horses. What did the last six look like?

wild horse equus ice age cave painting maija karala

You guessed it. Spotted.

These horses carried allele known as Lp, which produces a variety of coat colours known as the leopard complex. As hinted by it’s name, Lp allele interacts with other colour alleles in a complicated way, but the main principle is it produces a white horse with spots of whatever it’s “normal” coloration would be.

Heterozygote horses carrying a single copy of Lp, as all the horses in this study, have large spots close to each other, somewhat like a Dalmatian dog, though how clear the pattern is affected by other genes. If two of these horses breed, they might produce a homozygotic foal, which would be mostly white with much smaller spots. That makes a total of five wild horse colors.

A white coat with spots hardly sounds like a good way to camouflage from predators. As leopard complex is also associated with an eye deficiency causing night blindness, it’s hard to imagine how come they existed in the wild and were actually fairly common. The researchers seem a bit baffled themselves in their PNAS article, but suggests that the spots might have served as camouflage during snowy winter months or perhaps been favoured by sexual selection. Sexual selection doesn’t need to make sense anyway.

woolly mammoth mammuthus primigenius color polymorphism ice age megafauna maija karala

Nor were horses the only Ice Age animals that came in many colors. Some of the frozen woolly mammoth carcasses (Mammuthus primigenius) have tufts of hair left. It has long been known that in some cases the tufts are dark brown, but light and reddish in others. The late Finnish paleontologist Björn Kurtén thought the lighter hair tufts had just been bleached by time and, in his books, depicted mammoths as brownish black, much like musk oxes.

On 2006, a group of researchers tested the hypothesis by sequencing a gene called Mc1R of four woolly mammoths. The gene codes for a protein called melanocortin 1 receptor, which controls the types of pigment in mammalian skins and furs. A fully functioning copy of Mc1R leads plenty of brown and black pigments, or eumelanins, while less active versions replace them with reddish and yellowish phaeomelanins.

It turned out even the tiny sample of four mammoths contained two types of Mc1R genes: one that probably belonged to a dark mammoth as imagined by Björn Kurtén, and one hardly functional that was probably carried by a light reddish mammoth.

A less functional allele of Mc1R also causes the red hair and pale skin of red-headed humans. In 2007, it was discovered that the same sort of mutation also affected neanderthals. A study sequenced Mc1R of two neanderthals from Northern Spain and Italy, and showed they were both redheads. Their redhead allele was slightly different from that of modern humans, and probably originated independently, but it seems to have had much the same effect. Researchers suggest neanderthals might have had the whole range of hair and skin colors of modern Europeans.

susi pieni

Apart from humans, it seems like modern large animals are much less varied than their prehistoric counterparts. All Przewalski horses are bay dun, all bisons and mooses dark brown and all forest wolves more or less brownish grey. And it’s not just imagination. The genetic diversity of species from bisons to brown bears and wolves to musk oxes is just a fraction of what it was in the Pleistocene.

It seems this sudden loss of diversity happened almost simultaneously with three other things: the extinction of many whole species of steppe megafauna, the end of the last glaciation period, and the arrival of modern humans. Mammoths, woolly rhinos, sabre-toothed cats, cave lions, European hyaenas and musk oxes as well as American horses and camels were completely lost, among other creatures.

Whether this apocalypse was caused by themselves, changing climate or both acting together, the Arctic Eden of cave artists was short-lived.

References and further reading:

Gurney Journey: Sleuth work on Irish elk. The author of Dinotopia restores the Irish elk, with information on cave paintings.

Novels and essays of Björn Kurtén.

Pruvost et al. 2011: Genotypes of predomestic horses match phenotypes painted in Paleolithic works of cave art. PNAS

The Guardian: Cave art: what DNA can’t tell us about the spotty horses. An art blogger’s point of view on aforementioned study.

Wikipedia: Equine coat color. Information on horse coat colors and their genetics.

Römpler et al. 2006: Nuclear gene indicates coat-color polymorphism in mammoths. Science.

Lalueza-Fox et al. 2007: A melanocortin 1 receptor allele suggests varying pigmentation among Neanderthals. Science.

Hofreiter & Barnes 2010: Diversity lost: are all Holarctic large mammal species just relict populations? BMC Biology.

BBC Science: Neanderthals ‘were flame-haired‘.

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