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FROZEN MUMMIES of woolly mammoths and their contemporaries are rare enough to capture the public imagination and they invariably make big news. But are such frozen fauna just curiosities to gawp at – or can they make good science?

Work with a 36 000-year-old bison mummy found in an Alaskan gold mine has shown there is more to frozen mummies than novelty. The findings from the excavation and necropsy of Blue Babe, the mummy found near Fairbanks, Alaska, have generated new ideas about the processes that create frozen mummies.

Reconstruction of the bison’s anatomy based on preserved soft tissue shows that this Alaskan bison was closely related to European steppe bison pictured in Palaeolithic art. Canine punctures, claw marks and strangulation bruises provide the first direct evidence of an interaction between a Pleistocene predator and its prey: Blue Babe was killed by a lion.

Frozen fauna occur in permafrost-rich regions of the far north where cold and silt create the best conditions for preserving carcasses. The wonderful cartoons of woolly mammoths peering out of blocks of ice are, alas, only cartoons. Siberian and Alaskan mummies were buried in earth; there is no evidence that these animals fell into glacial crevasses. More exotic theories of preservation probably arose because great wedges or veins of ice are sometimes present in permafrost soils. This ice can provide clues about a mummy’s burial and preservation. The underground migration of moisture which creates masses of ice desiccates the soil, and dries out the bodies of large mammals in the process. Frozen mammoths are as desiccated as an embalmed pharaoh and fully deserve ‘mummy’ status. Unfortunately, most Pleistocene mummies have simply been pulled from the thawing earth and promptly washed – leaving a clean corpse, but little else.

This has been particularly true in Alaska, where virtually every Pleistocene mummy discovered in the past century or so has been found by gold miners. Each spring, along with the Sun and the geese, placer miners return to the north. Placer, or surface, mining is now regulated to protect the environment, and the number of miners is dwindling, but 50 years ago Alaskan placer mining was big business. Massive dredges and extensive water pipelines moved millions of cubic metres of late Pleistocene silts to expose gold-bearing gravels buried just above bedrock. The miners used powerful jets of water to thaw and erode deposits of muck and peat. They reshaped entire valleys in this search for gold – and exposed innumerable fossil bones and several frozen mummies.

The sheer numbers and richness of fossils of large Pleistocene mammals from Alaska and Siberia formed the basis for many ideas about the far north during the ice-free Pleistocene epoch. The fact that so many of these fossils were of grazing animals specially adapted to grassy diets led palaeontologists to suggest that a steppe vegetation must have circled the top of the globe like a grassy collar. Fossils of the woolly mammoth (Mammuthus primigenius) are found from Alaska and the Yukon Territory westward across Eurasia to England. Fossils of wild horse (Equus ferus) and steppe bison (Bison priscus) turn up with mammoth almost everywhere. Saiga, reindeer, musk oxen, lion and wolf fossils are also found across this entire area. Species with a more restricted distribution include woolly rhino, bonnet-horned musk oxen, camel, sheep and goats. The occasional appearance of frozen fauna, of individual animals preserved relatively intact for hundreds of centuries, allows us to investigate this Pleistocene community, the ‘mammoth steppe community’, with greater clarity than assemblages of fossilised bones.

Although frozen mammoths claim most publicity, the steppe bison was apparently a more numerous member of the mammoth community. We can gather many details about the appearance of European steppe bison from images of these animals in Palaeolithic art. But there were no people in North America to record the way Alaskan steppe bison looked. The discovery of a new mummy provides a rare opportunity to address an assortment of questions, from theories about past climates, extinctions and the evolutionary relationships between species, to very immediate issues of how mummies are preserved and how this particular animal died.

Better than gold

We were confronted with a unique opportunity to tackle some of those questions in the summer of 1979, when a gold miner, Walter Roman, notified the University of Alaska that the legs of a large mammal were protruding from a wall of frozen earth at his mine just north of Fairbanks. Once the animal was exposed, we had to work out a strategy for excavating the animal very quickly. Work began as the bison (identified by its exposed hooves) slowly thawed from the bank of organic silt.

Eventually, large horns and male genitals came into view; the mummy was a mature male. Meanwhile, oxidation of an iron-phosphate compound on the hide was causing azure warts of vivianite to grow on the skin, turning the body blue. This prompted us to call the mummy Blue Babe, after a famous giant oxen belonging to Paul Bunyan, the mythic hero of logging stories from the American northwoods.

The emerging mummy was encased in mud but we made no attempt to clean it at the mine. Even without cleaning, it was obvious that the carcass was not complete. It had been partly eaten and scavenged; skin was torn open and some bones had been chewed. For the next two weeks we washed the thawed silt surrounding Blue Babe and collected and refroze samples for later analysis. We mapped the position of the carcass and the surrounding stratigraphy, looking for clues about how the bison died and how it came to be buried. Hair over the front part of the body was still held in place by frozen silt but hair follicles had slipped their attachment to the skin, so as we removed the hair we mapped its location on the carcass. The bison’s head was the last part to appear; it was remarkably well preserved and had not been attacked by scavengers.

Blue Babe had a brief moment in the summer sunlight and was returned to frost for safekeeping – this time in a freezer at the university’s Institute of Arctic Biology. Walter Roman resumed his mining and the silt that had held Blue Babe was completely thawed and washed away.

Soviet palaeontologists, who have had more chance than most to look at frozen mummies, have found that most mummies come from two periods: around 11 000 and 35 000 years ago. The radiocarbon date from Blue Babe’s skin placed him in the earlier period, around 36 000 years ago. Because this is near the limit of radiocarbon dating, which makes the date susceptible to error from small contamination, we also dated a stick taken from silts a metre above the bison. This date of around 31 000 years ago suggests that the initial date was probably correct.

Blue Babe had lived during a slightly wetter and warmer period between the more intensely cold and arid peaks of the last glaciation. Analyses of fossil pollen from Alaska shows that trees recolonised the mammoth steppe during the time Blue Babe lived. But the proportion of tree pollen to other species remained low. This, along with the fossil remains of grazing animals, suggests that the Alaskan landscape kept much of its cold steppe character through this period.

Windblown loess blankets much of the Alaskan interior, but the valley deposits that held Blue Babe were reworked silt: loess and organic material washed downslope by rain or melted snow. The silt deposits around the mummy were a mixture of thin, finely bedded layers from regular small-scale erosion and occasional deeper layers washed down by heavy rain or melting snow.

The two periods that the Soviet scientists identified probably represent times when conditions were right for the deposition of silt. Burying a carcass is the first step in making a frozen mummy. During full glacial periods, there was not enough moisture for erosion to lay down silt, and during interglacials, as today, the covering of vegetation was so complete that it left very little soil exposed to the elements.

Stratigraphic detail at the mine showed that a stream leading into the valley could have deposited enough silt to cover the body. There is no need to invoke a massive landslide or the cave-in of a riverbank to explain how this mummy formed: a carcass buried under a layer of silt flowing over frozen soil would decay little during the brief northern summer. And as the layers of silt accumulated over the carcass, establishing a new ground surface, succeeding winters would pull the zone of permanently frozen soil upwards, incorporating the body in a silty deep freeze.

Fortunately, we had the chance to meet some Soviet palaeontologists and discuss their experience with the Siberian mammoths and other mummies. This was invaluable in planning Blue Babe’s necropsy and in deciding how to display the body when all the work was done.

The first step in our necropsy was to screen the bags of silt collected at the excavation. We sent insect carcasses to appropriate specialists and silt samples to experts in pollen analysis. Next, we moved the mud-laden tangle of the mummy’s torso and legs from the freezer to the laboratory. As we cleared away the mud, the extent of scavenging became more apparent. The hide was torn down the back and meat on the hams, back and shoulders and many vertebrae were gone. The bison’s legs were intact and the sternum and lower ribs were present. Perhaps this animal had simply died of hunger or old age, with its legs tucked underneath, protected from scavenging? Annual constrictions in the bison’s horns, and the rings in a section through an incisor, suggested that the animal was 8 or 9 years old. An incomplete winter ring in the root of the tooth and the presence of winter underfur put the time of death in late autumn or winter. This was corroborated by the thick deposits of fat in the carcass. By late winter these reserves are gone. But an old or sick animal does not normally have thick subcutaneous fat. So had this bison met a violent death? Eventually, as the silt was cleared away, long scratch marks began to appear on the rear of the hide. The scratches were in clusters of three and four parallel lines and they cut deeply into the lower layers of the skin. Wolves do not use their claws to kill prey. Grizzlies have powerful claws, but because they do not retract they are too blunt to cut repeatedly into a thick hide. Modern grizzly bears use their claws mostly for digging out ground squirrels. The hide also bore the puncture marks of large canine teeth, in pairs, about 8.5 centimetres apart. The only predator in Pleistocene Alaska capable of such sharp-clawed scratches and with canines this distance apart was a large cat belonging to the genus Panthera, most likely a lion (Panthera leo).

Later, when we prised back the bison’s heavy facial skin, we found clotted blood and additional punctures on the snout. Lions kill smaller animals with a bite to the neck that damages the central nervous cord, but larger prey, such as wildebeest and buffalo, require a different approach. A lion kills these larger species by strangulation – by enclosing the victim’s snout in an airtight bite.

The final clue was a fragment of a carnassial tooth embedded in the bison’s skin. Carnassial enamel is unusually thick in Panthera. No other terrestrial carnivore in Pleistocene Alaska had such thick enamel.

Lions were important predators in the mammoth steppe community: lion fossils from sediments of similar age have been found in the Fairbanks area, not far from where Blue Babe was buried. But this is the first mummy of an animal identifiably killed by a lion. In fact, no Pleistocene mummy has ever been excavated which could be shown to have been killed by any kind of predator.

Some 20 kilograms of red muscle remained in the carcass. African lions normally consume the entire carcass of a large herbivore; gorging, resting and then eating again, unless driven off by hyenas. But, assuming that the bison was killed in winter, once the Alaskan lions opened the bison and began eating, they would have had no more than three or four days before the remaining tissues were completely frozen. According to the zoologist George Schaller, who studied the lions of the Serengeti, two or three African lions could not eat a mature bull bison in this time. Once the carcass had frozen, those parts encased in skin would have been very difficult to dismember. We suspect that the fragment of tooth left in the mummy’s skin was broken off when a lion tried to chew the frozen hide.

There are few records of solitary lions killing African buffalo. As Blue Babe was comparable in size and was armed with horns as long and sharp as an African buffalo’s, and as Pleistocene Alaskan lions were no larger than living African lions, it probably took two or three of them to kill the Alaskan bison. The uneaten meat remaining on the carcass, and the portraits of lions we see in Palaeolithic art both suggest that the lions of the mammoth steppe lived in smaller prides than those of East Africa. Palaeolithic artists never pictured more than three lions together and their lions did not have the large mane that many African and Asian males wear. Large manes are social paraphernalia. The most elaborate manes grow on lions in regions where there are enough herbivores to support large prides. Males in large prides do less of the hunting but probably experience more competition from other males. A large mane might be a drawback during a stalk, but it is a definite advantage in the dominance stakes. In regions that support smaller prides (and where competition is less pronounced), male lions have manes that are less contrastingly coloured, and in some places males are virtually maneless. The northern steppe of the Pleistocene supported a much smaller number of herbivores than the African savannas do today, hence the smaller prides and maneless males.

There is evidence that other animals scavenged the bison carcass after the lions abandoned it. Strings of muscle connective tissue and tendons on the upper limb bones of the mummy are characteristic of ravens and other scavenging birds. Gnaw marks on bones indicate that smaller mammalian carnivores, such as dogs, also tried feeding on the carcass. But flesh in the legs and head was encased by the frozen skin.

Blue Babe must have been buried soon after the spring thaw because there were no cases of fly pupae and few bits of scavenger beetles with the mummy. Today carcasses of animals killed in winter are flyblown and consumed by maggots, leaving a mat of pupal cases by early spring. We know that blow flies were present during the Pleistocene because their remains are common among other fossils from Alaska. In Blue Babe’s case, decay seems to have been brought on by enzymes rather than microbes.

Fleshing out the bison’s life story

The soft tissue preserved in Blue Babe and other frozen animals can help to flesh out the story of these extinct species. Details of appearance reconstructed from such mummies provides insights into the social behaviour and ecology of Pleistocene animals as well as their relationships to living species. The colour and patterning of Blue Babe’s coat suggests that it was closely related to the Eurasian steppe bison. The coat was reddish ochre with black points on the legs, tail and face, but there were no large pantaloons of leg hair or a large cap of dense hair as in modern American plains bison. The tail was short, shorter than tails of any other American bison and shorter than tails of past and present Eurasian bison. ÐÓ°ÉÔ­´´s at the Institute of Arctic Biology are trying to isolate DNA from the mummy to make a direct genetic comparison with today’s species.

The lack of a large ‘bonnet’ on Blue Babe’s face and head and the shape and size of his more forward-pointing horns are direct evidence that steppe bison did not engage in the violent running clashes of modern plains bison – corroborating evidence from the animal’s skeleton. In conflicts with other bulls, the Alaskan steppe bison must have behaved more like European bison, which fight and lunge from a standing position. The skin on the mummy’s neck and face was unusually thick, presumably a defensive armour for pushing battles in which each bull attempted to shove the opponent’s head to one side in an attempt to stab his neck and shoulders with long sharp horns.

The extraordinary difference in the size of the body and horns between the sexes in steppe bison suggests that, outside the reproductive season, males lived singly or in small groups apart from the female herd in an even more extreme manner than either species of bison living today. Such a solitary life gives bulls advantages in feeding, but it also makes them more vulnerable to predation – especially from large social predators such as lions.

Many northern Pleistocene animals were very large, reflecting the environment in which they lived. Today, tundra and coniferous forest cover this region. The biomass of plants is tremendous, but much of it is made up of plants such as spruce and alder, which grow slowly and defend their hard-won tissues with poisonous chemical compounds. Because of this natural toxicity, only a small part of the mass of plants is edible. The arid and windy Pleistocene landscape may have supported fewer plants but large mammals could at least eat them. Grasses are adapted to grazing: they contain few toxic compounds to fend off herbivores; and they grow rapidly in the spring and can afford to have standing dead tissue grazed every year. The shallow snow cover and lower plant profile also meant that the spring thaw was relatively quick. Long growing seasons (for the north) and long summer days produced extremely rich forage and resulted in some gigantic animals such as red deer, moose and bison.

The lack of trees for shelter and the intense cold during full glacial periods kept people out of the northern mammoth steppe. But as the climate grew warmer and wetter and the steppe began to retreat around 11 000 or 12 000 years ago, humans followed the advancing boreal forest, eventually entering the New World. Wild horses and saiga antelope were confined to remnants of the steppe at high altitudes in Central Asia. As the landscape changed, regional extinctions sometimes added up to complete extinction; woolly musk ox squeezed through, the woolly mammoth did not.

These frozen fauna are literally a cause of wonder: they stir the imagination, making distant times and events suddenly seem very real. Is it that a mummy like Blue Babe embodies mortality? That it stays the laws of appearance and disappearance that are the norm? Whatever the explanation, the dramatic promise of a mummy draws children – and adults – into dark museum rooms, but something more causes them to stay, to read every label and still have questions days later.

The story of the Alaskan bison is one that holds lessons for us today, in the face of rapid global change. A diffuse and compound issue such as global warming needs many threads of facts guying it into the past. Blue Babe provides one such thread. That bison walked on dusty trails tracked by mammoth and horses, yet changes of a few degrees and very slight shifts in moisture transformed the mammoth steppe into taiga and boreal forest.

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CHECKING UP ON THE PALAEOLITHIC CAVE PAINTERS

THE wealth of Palaeolithic art has been very useful in reconstructing the appearance of the Pleistocene mammals that roamed Eurasia. These artists knew woolly mammoths and rhinos from first hand acquaintance and they were meticulous observers. But there is considerable ‘artistic licence’ in Palaeolithic art: bright splotches of colour, strange stripes, foreshortened legs, and other features require discrimination. For many details, we can only accept their view of it, because all we have to check against are bones. Frozen mummies provide scraps of skin and hair from which we can reconstruct the animal – and gauge the reliability of the cave artists’ vision.

Bison in Palaeolithic art do not look like either species of bison living today. ‘Cave bison’ have shorter, darker hair on the head, no pantaloon on their forelegs and other exotic features. The pelage found with Blue Babe was very similar to the bison portrayed in Palaeolithic art, such as the cave paintings at Altamira in Spain (right). Little did those artists know that critics would be assessing their work tens of thousands of years later – and giving them full marks.

Dale Guthrie is a palaeontologist and biology professor at the University of Alaska, Fairbanks. Mary Lee Guthrie is a writer and artist. Frozen Fauna of the Mammoth Steppe, by R Dale Guthrie, is published by the University of Chicago Press.