Fig. 2.26. Close-up of vivianite on the furrowed scalp between the horns.
After Blue Babe was mounted we restored his color by taking vivianite collected from other bones and dusting it over the skin. A thick mixture of vivianite and shellac was also dabbed into the craters remaining on the head skin to re-create the blue warts.
3
RECONSTRUCTING BLUE BABE’S DEATH
Season of Death
Several features of Blue Babe’s carcass provide clues about the season in which the bison died. The first clue was evident when we excavated the carcass. Although hair had “slipped” from the skin, frozen muck held much of the pelt in place, at least on anterior body parts. This allowed us to sample the hair, mapping its length and color (fig. 3.1). It was obvious from these early samples that both the guard hairs and the fine underfur of the winter pelt were present and mature. Clearly, the bison had not died between spring, when pelage is shed, and early fall, when new underfur grows in, so June, July, and August were excluded as time of death.
The second clue came later, during the necropsy Although much of the carcass had been eaten by a carnivore or scavenger, thick fat deposits remained, particularly around the sternum. The accumulation of fat in autumn or early winter is a universal characteristic of northern ungulates; during the long winter these fat reserves are depleted. From observing Alaskan animals over several decades, I can say that no ungulates enter the spring with significant fat reserves. In fact, of the dozens of sheep (Ovis dalli), moose (Alces canadensis), caribou (Rangifer tarandus), and bison (Bison bison) I have seen killed in mid- and later winter, few have much fat anywhere in their body. Roe (1951) quotes Richardson as stating that in early winter he had killed many plains buffalo that were fat, but beyond midwinter, buffalo were invariably lean. Large deposits of fat in the mummy strongly suggest the bison died during autumn or the first part of winter.
After Blue Babe was excavated, I sent an incisor from his lower jaw to Matson’s, a private lab that specializes in sectioning mammalian teeth to determine age and season of death. Gary Matson’s exam found summer growth complete but the winter annulus not yet fully developed, so he concluded that the bison died in autumn or early winter.
Horn annuli can also indicate the season of death. Northern bovids begin laying new horn from the base each spring. Growth continues until autumn, then stops until the next spring (Fuller 1959). During this dormancy a constriction in the horn forms a winter annulus similar to that in tooth root cementum. Blue Babe’s last horn segment was complete, and a winter annulus was beginning to form. The final segment was 22 mm wide on the dorsal surface; the segment of the penultimate summer was 26 mm, while the one before that was 35 mm and the one before that 46 mm. The final horn segment was the size predicted for a complete summer of horn growth. In contrast, a final segment 5 mm long, for example, would have indicated death early in summer.
Fig. 3.1. The necropsy. Blue Babe was taken out of the freezer, and we began to carefully clean the carcass, looking for clues to the bison’s death and mode of preservation. (Photo by Don Borchardt)
Other characteristics of the carcass affirmed these early assessments that death occurred soon after freeze-up. Blue Babe was incompletely eaten, and the carcass was not fly-blown. Braack (1986) showed that, in South Africa, flies reduced a carcass to bones in five days during summer and fourteen days during winter. Muscle scraps found in the adjacent muck were actually still red, as were the muscles that were still attached. The upper or dorsal part of the body was eaten. Most of the vertebrae were missing, and I suspect they were eaten. Neural spines on the few remaining vertebrae were gone, and only scraps of ribs remained. Ventral body parts as well as the head were relatively untouched. This pattern of scavenging and preservation led me to think the bison was probably frozen after a predator had eaten part of the carcass. When a large carcass freezes, the skin becomes almost like sheet steel; a heavy, frozen hide is difficult for a predator or scavenger to penetrate.
A Modern Blue Babe Experiment
While I was working on Blue Babe’s carcass in the laboratory, I heard that fifteen bison from a herd introduced at Big Delta, a hundred miles south of Fairbanks, had died after drinking melted snow produced by a spill of liquid urea fertilizer. With permission from the Alaska Department of Fish and Game, I obtained the largest animal, a bull about 3 years old. The weather had been cold −30° F(−34° C), and the bison was frozen. A man with a wrecking track helped us hoist the body into a pickup, and we returned home to Fairbanks. There we tied the bison to a tree and drove the pickup out from under the stiff carcass; it landed in packed snow I had no detailed plans; I just hoped to leam something from watching the Big Delta bison decompose in the spring.
During that first night there was a light snowfall. I noticed that snow on the bison was melting, which seemed an odd thing to happen on a frozen animal. After three days, and another light snowfall, it was obvious that this bison was not totally frozen but was continuing to ferment inside, like a compost pit within a blanket of thick hair. By this time the hair was starting to slip. I decided to take out the viscera to allow complete freezing. At −20° F (−12° C), I removed the steaming rumen and emptied the rest of the abdominal cavity. Within two days the carcass was stone hard.
Ravens and neighborhood dogs began to work on the frozen bison without much effect. They slowly cleaned exposed meat and ribs in the body cavity but the bison’s legs and head remained untouched, encased in the impenetrable skin. Most scavenging occurred in late April during the warmth of breakup, and soon as the snow was gone, flies began to assemble. Very soon thereafter, before much green was showing on nearby plants, the carcass was a pulsating mass of maggots. A little more than a week later it had settled into a bed of black blowfly pupae cases about 50 mm deep. Nothing remained but bones which had taken a light brown stain that I judged to be a by-product of the maggots. Local dogs no longer bothered the bones.
This smelly exercise taught me several lessons about neighborly relations and decomposition. An unopened animal continues to decompose after a fresh kill, even at very cold temperatures, because the thermal inertia of its body is sufficient to sustain microbial and enzyme activity as long as the carcass is completely covered with an insulating pelt and the torso remains intact. Therefore, it is unlikely Blue Babe met a natural senescence or disease-caused death and was later scavenged, because the preservation of remaining muscle, the solidly preserved epidermis and dermis, and the firmness of connective tissue and fat all indicate the bison carcass was opened immediately after death.
The especially good preservation of the mummy’s head is also best explained by a winter kill. No part of the head was more than a few centimeters from the cold, and the bison’s large horns would have acted as radiators, cooling the head rapidly after death. Rapid cooling would slow decomposition and render the head inaccessible to predators and scavengers, freezing it solidly soon after death. Finally, the head and lower limbs are the last parts of a large carcass that carnivores consume, so these would have had more time to freeze (fig. 3.2).
Apparently, Blue Babe died with his legs tucked under his body. Perhaps the legs did not fare as well as the head because snow is a good insulator. Nevertheless, they did preserve relatively well, with small patches of hair clinging at least to the forelegs. As the hind legs were almost totally exposed when I first saw the carcass, I cannot say if leg hair had been present in the adjacent silt, as it was over most of the head.
My observations of the decomposing Big Delta bison were thus consistent with ideas I was beginning to have about the nature of Blue Babe’s death. To forestall all decomposition and preserve so well, the carcass had to have been opened quickly. Also, the body had to be buried quickly, quite early in the spring, before blowflies were active.
Fig. 3.2. Heat loss and decomposition. At winter temperatures the head and legs of a large mammal cool rapidly after death and soon freeze. Tough, frozen skin makes these parts difficult to sca
venge. Anaerobic activity in the rumen, however, continues to generate heat and keeps the torso warm even at low temperatures. This is aided by the insulation of dense body hair. If the body is opened by predators soon after death, it cools rapidly and muscles and viscera freeze completely within a day or so.
Blue Babe’s Season of Burial
In addition and closely related to the clues delimiting Blue Babe’s season of death, the carcass yielded information about why Blue Babe died and when he was buried. We know that preservation of a relatively fresh-looking mummy such as Blue Babe required burial and temperatures near or below freezing. For instance, the carcass could not stay above ground all summer, exposed to microorganismal decomposers or insect scavengers. These would have quickly destroyed soft tissue.
If our conclusion about an early winter death is correct, the carcass was exposed all winter to avian and mammalian scavengers, because the bison could not have been buried when the ground was frozen. Today the ground is hard in Fairbanks between October freeze-up and spring thaw in late April or May, and there is no reason to suspect this pattern would have been much different when Blue Babe lived.
Once spring arrived, if the bison carcass was exposed for even a week it would have attracted insects, particularly blowflies. Pupae cases are common in Alaskan Pleistocene fossil bones—they are found wedged into foramina and in brain cases—so we know that blowflies were present in Pleistocene Alaska and that they attacked large mammal carcasses. Despite considerable search, no pupae cases were found with Blue Babe, either in the carcass or in the silt immediately surrounding it. Likewise, identification of insect parts from silt around the bison did not show an unusual assortment of scavenger beetles, which are abundant around decaying carcasses. (See identification of insects in Appendix A, by John V. Matthews, Jr., Canadian Geological Survey, Ottawa.)
During the spring, bears and other northern mammals regularly search for winter-killed animals, locating them with remarkable acuity when the carcasses begin to smell from enzyme action or microorganismal decomposition. Today a carcass as large as the bison does not long escape the notice of mammalian or avian scavengers and probably would not have lasted long in the Pleistocene either.
The high degree of tissue preservation, incomplete scavenging, lack of concentrated remains of insect scavengers, and geological information all indicate that Blue Babe was buried in the spring by the runoff of snowmelt. Today the ground is still frozen when snow melts, and runoff water moving through the vegetation mat carries virtually no inorganic particles. However, under conditions in the Pleistocene, with far more exposed soil, spring runoff was likely very different. At first I had assumed that snowmelt could not wash frozen silt so early in the spring; I assumed Blue Babe must have been buried by later spring rains. But during the spring of 1985, I noticed wholesale erosion through snowmelt runoff of naked soil at several construction projects left unvegetated during the previous building season. Because of these observations and the absence of blowflies, I now rule out burial from silt transport by spring rains.
Many fossil skulls and bones in the paleontological collections at the University of Alaska Museum do have fly pupae associated with them. In these cases, it is possible that soil removal downslope from summer rains rather than from spring snowmelt must have figured prominently in their burial.
Additionally, I believe Blue Babe was completely buried in a short time because there is little difference in the way various body parts are preserved. There is no evidence of horizontal gradations of preservation that would be caused by successive layers of silt accumulation. All parts, including bones scattered around the carcass, are equally fresh looking, as one would find them in winter and not after a summer of decomposition and weathering. That so many hair tufts, strings of connective tissue, small and large fragments of bone, entire bones, pieces of skin, and small bits of muscle were still scattered around the carcass strengthens the above point and tells us there was negligible retransport of the carcass by physical processes. These scraps were located as they would have appeared after several months of winter scavenging, with some red muscle buried in the snow and head and legs protected by frozen skin.
Haynes (1982), in his studies of bison killed by wolves in Wood Buffalo Park, Canada, has shown that wolves eat the bison in a fairly consistent pattern. A large wolf pack is capable of dismembering and consuming the soft parts of an entire bison. Although Blue Babe’s remains do not conform to this pattern, they are similar to one of Haynes’s mature bull bison that froze (fig. 3.3) before the wolf pack could complete its consumption of soft parts. In this particular case, portions of the visceral cavity and upper rump muscles were eaten before they froze. One month later, most of the ribs had been eaten, and parts of pelvic bones and many projecting parts of vertebral bones had been chewed off. The head and lower limbs still retained their skin; they were essentially untouched. This sounds similar to Blue Babe’s appearance.
Fig. 3.3. Bison in Wood Buffalo Park, Canada, partially eaten by wolves before it froze. (Photo by Gary Haynes)
Cause of Death
At first, during the excavation process, I guessed that the bison’s death was not caused by predation because the carcass seemed relatively intact when it was still embedded in the silt. Much edible flesh remained, but signs of scavenging were obvious too. Perhaps, like many present-day carcasses I had seen, Blue Babe died in the winter, froze, and was chewed on and pecked at by an array of scavengers. Late winter is a common time for ungulates to succumb to accumulated winter debilitation. I pictured a late winter death for the bison, and the winter underfur I collected was consistent with that interpretation.
It was not until the necropsy was underway that evidence inconsistent with my first idea emerged. I found thick deposits of fat that were quite unexpected. I had never seen a fat animal, especially one with thick subcutaneous fat, die from internal causes in spring-time. Deaths early in winter from causes other than predation are not common. Maybe Blue Babe had been killed by a predator, but what predator could kill a strong bull bison?
The next surprise during the necropsy was finding long scratch marks on the rear of the hide (see figs. 3.4 and 3.5). These scratches scored deeply through the epidermis into the dermis but failed to break through the thick hide. Occurring in clusters of three and four parallel lines, the scratches looked just like those made by claws of a large predator. Today many large mammals in Alaska (my basis of comparison) are killed by wolves (Canis lupus), but wolf kills do not show such large scratch marks. Canids do not use their claws to kill or to dismember a carcass. A large bear was the next culprit I considered, but grizzly bear (Ursus arctos) claws are mainly used to excavate fossorial rodents, not for clinging to large prey Bear claws are powerful, but they are not retractile like a felid’s and hence are not very sharp. Bears are probably incapable of making deep scratch marks like those we found in the bison hide.
Another large ursid in the Fairbanks area during the late Pleistocene, the giant short-faced bear (Aictodus simus), does not seem to have been a rodent excavator like the grizzly. This Pleistocene short-faced bear may have been a more active predator (Kurtén and Anderson 1980), and perhaps it was capable of killing a bison. Ursids are generally solitary hunters, however, and a bison as large as Blue Babe, in healthy condition, with sharp horns to defend himself, would have been a formidable challenge. I was not comfortable with the hypothesis that a bear caused Blue Babe’s death. The scratch marks strongly suggested a large felid with sharp, sheathed claws (Gonyea and Ashworth 1975). Gradually, I backed into considering the unlikely: Blue Babe may have been killed by a lion.
Fig. 3.4. Blue Babe’s flayed skin. Predators opened the carcass from the top, so genitals and sternum are in the middle of the hide. A thin line indicates the cut made during excavation when the exposed torso and legs were cut away. Scratches are also shown. The tail was found adjacent to the carcass, presumably bitten or torn off from the bison when fresh.
Fig. 3.5. Addition
al scratches found on the lower hind limbs.
Continued mapping showed that the scratch marks occurred on the bison in the same places as Schaller (1972) and Sinclair (1977) found lion (Panthera leo) scratches on African buffalo (Syncerus cafer). Sinclair found scratches on the back and flanks of buffalo that lions had tried to grab and throw off their feet, a necessary first step for lions to kill such large animals. Further literature search convinced me that these claw marks are a characteristic indicator of large felid kills or attacks. Sinclair (1977) found that many buffalo carried such scratches from their past encounters with lions.
Fig. 3.6. Blue Babe’s head wounds. Scratches and punctures could be seen on the head before we removed the skin. The lower lip was torn and partially scavenged. Whether this was done at the time of death or later is uncertain.
Fig. 3.7. Clotted blood on inside of skin. Clotted blood in the middle of the nose and face skin shows trauma occurred soon before death. This clot and breaks in the facial skin support the idea that Blue Babe was strangled by a hold on the nose. Other traces of bruising were evident over the forward part of the orbit, possibly from violent handling by the lion.
I was stunned—an Alaskan lion—dare I even think it? Later in the necropsy we indeed found a puncture mark on the snout (fig 3.6) and blood clot stains on the interior of the nose skin (fig. 3.7). This hemorrhaging indicated the injury had occurred while Blue Babe was still alive. Because large bovids have exceptionally thick skin and large muscles on their necks, lions and tigers cannot use their regular neck bite to kill these animals; instead lions actually kill bovines by strangulation. Using claws for a secure hold, a lion will throw a buffalo down and clamp the buffalo’s entire nose and mouth in a firm bite (fig. 3.8) or clamp the trachea closed (fig. 3.9). The lion must hold the buffalo this way until it suffocates (Schaller 1972). Evidence was mounting. Incredible as the idea first seemed, Blue Babe apparently was killed and then partially eaten by one or several lions.
Frozen Fauna of the Mammoth Steppe: The Story of Blue Babe Page 9
