Frozen Fauna of the Mammoth Steppe: The Story of Blue Babe

by Guthrie, R. Dale

  We can compare this picture of Blue Babe with the images of his European contemporary, the B. priscus, drawn by Paleolithic hunters. Of course one must be cautious when using art works to determine actual pelage pattern (Guthrie 1984c), just as a single portrait offers only suggestions, not proof, about details of appearance. But cave pictures of bison are like a set of portraits done by different artists of the same model. Given certain caveats, one can argue that if a general pattern exists, it very likely relates to what was actually seen.

  Although bison are among the most common animal portrayed in Paleolithic art (Leroi-Gourhan 1982), only a few of these drawings and paintings are fully colored (figs. 4.11 and 4.12); most bison are drawn in outline and lack body tones or color. Also, there is a wide variability in the pictures which surely did not correspond to an actual variability in nature. The bison are always positioned laterally in the paintings, and the interior of the body usually has the same color. Among the bison that are fully colored, the body interior is dark reddish, while the periphery, particularly the cervical and posterior thoracic hump, the tail, legs, and face are regularly darkened or painted black. This coloration differs from living bison, but is very similar to Blue Babe’s, at least to the portions for which we have hair.

  Fig. 4.11. Color pattern of steppe bison in Paleolithic art. A dark wedge runs from rump to elbow, and a smaller dark wedge appears at the posterior base of the hump. A dark mane, legs, and head leave a light side panel in the shape of a tobacco pipe. These samples are from (a) Le Portel, (b) Altimira, (c) Niaux, (d) Lascaux, and (e and f) Santamamine.

  Fig. 4.12. Steppe bison in Paleolithic art. (See also those of fig. 4.11.) Further examples from (a) Fontanet, (b and c) Les Trois Frères, (d) Le Portel, (e and f) Niaux, (g) Font-de-Gaume, (h) Lascaux, and (i) Altimera.

  Flerov (1977) discussed hair color and hair length of a two-and-a-half-year-old female Pleistocene bison mummy found on the Indigirka, USSR. Unfortunately, females have different color patterns than males among living American bison, and this dimorphism probably held true for Beringian bison as well. The color patterns Flerov reports are roughly similar to those I have described for Blue Babe except his are lighter in every individual area. The most notable difference is a very light leg coloration (“light yellow ochre”) of Flerov’s female mummy; no living bison has lightly colored legs. This could be the color in life, or the leg hair could have been bleached in a manner I described earlier.

  Flerov (1977) also describes a slightly different pattern of hair length from that of Blue Babe. Unfortunately he does not directly describe the hair length for the young female, but uses her to reconstruct how bulls must have looked. He proposes short pantaloons on the rear of the forelegs; there is no trace of these in Blue Babe. Flerov does describe the “rusty-ochre” and “rusty-cherry” color of the neck and shoulders that I saw on Blue Babe.

  Horns and Hooves

  Unlike most fossil bison skulls found in Alaska, which have poorly preserved sheaths on their horn cores, Blue Babe’s horns were in almost original condition. Horn keratin had undergone some chemical deterioration and was brittle, but the surface remained, appearing as it must have in life. The horns are a deeply pigmented black and show none of the porosity that appears as a white frosting among some living black-horned bovids, including some individual bison. The tip end, or distal half, of the horns is highly polished, and one cannot see the more distal annual growth rings. There is a broken terminal portion on each horn, which is unusual among bison fossils from Alaska; most terminate in unbroken slender sharp points (Guthrie 1980). Despite Blue Babe’s broken tips, the horns still have sharp points, because the lost portion was like a cone pulled from the distal end, exposing the tip of an underlying sharp cone. (Large sharp horns are an important clue to the behavior of steppe bison, which I discuss in chapter 7.) Blue Babe’s horns are much larger than those of any living bison, but fall in the lower size range of steppe bison.

  Hooves

  Blue Babe’s hooves came off during the excavation. They were bagged and frozen, but later, when thawed and dried, the hooves curled, cracked, and came apart. Nonetheless, I have photographs taken of them during the excavation as well as the terminal phalanges that fitted inside the hooves. These differ in no noticeable dimension or shape from living American bison.

  Flerov (1977) proposed that the hooves of Beringian Pleistocene bison were considerably larger than those of living species, although Vereshchagin and Baryshnikov (1984) disagreed. Flerov shows the forehoof of an old European bison bull, Bison bonasus, and compares it with a two-and-a-half-year-old Pleistocene cow. The cow has hooves the exact appropriate size and shape for an American bison of that age (Murie 1954), but Flerov’s illustration of the foot of the European bison bull does not fit my photographs of B. bonasus feet. Either Flerov mistakenly used a hind foot of a European bison (which has the same size and shape as the one shown by Flerov), or the European bison he used had dramatically different-shaped hooves than ones I have examined. From a search of many slides of European bison the latter does not seem to be the case.

  I think that in fact the slightly overlapping, inward-curved hooves Flerov describes (1977) as being adaptive for swampy environments, are simply late winter hooves showing lack of wear, as occurs in winter among living bison. Bison on snow-covered ground do not wear down their hooves, nor do they regularly use their hooves as horses do to dig through snow for food. I have seen musk-oxen (Ovibos moschatus) with similar, and even more extreme, overlapping hooves in the spring. Hoof shape and size are very important in understanding an animal’s adaptation to different substrates; they are discussed in chapters 8 and 9.

  Skin Thickness

  Although skin thickness is not directly related to Blue Babe’s appearance, it tells part of the story of how behavior affects external anatomy. Geist (1971a) noted that patterns of skin thickness vary considerably from one ungulate species to another and, further, that skin thickness is correlated with mode of combat. Geist compared sheep (Ovis canadensis) with Rocky Mountain goats (Oreamnos americanus) and found that while sheep have thick skin around the head and thin skin on the posterior of the body, this pattern is reversed in Rocky Mountain goats. Their face and shoulder skin is thin, while the skin on their flanks and posterior is thickest. Sheep are head clashers, and occasionally their horns slip onto the forward part of the opponent’s body. Rocky Mountain goats fight standing side by side, facing opposite directions, and dig their sharp horns into one another’s flanks. For both sheep and goats, thick skin thus acts as defensive armor, decreasing the damage of an opponent’s blow.

  Fig. 4.13. Skin thickness. Presumably the thick skin, especially around the head and neck, was a defensive armor against an opponent’s sharp horns. The thinner torso and leg skin allowed supple movement. (Thickness shown in millimeters.)

  Even when the mummy’s neck and head were first exposed during the excavation, it was obvious that skin in this area was unusually thick. I have plotted skin thickness in figure 4.13. Skin around the distal part of the legs is 3–4 mm thick, and over the lateral part of the body skin averages 6 mm. Along the dorsal surface, over the sacrum and lumbar area, it is thicker, ranging between 8 and 16 mm. Skin on Blue Babe’s head is by far the thickest, 22 mm—measuring nearly one inch.

  Age

  Much of Blue Babe’s appearance would have been determined by his sex and age. We know from horn size and the presence of male genitals that Blue Babe was a male. I used several methods to determine Blue Babe’s age because age at death is so critical to other elements in the analysis. For instance age is the key to estimating rates of tooth wear, which, in turn, has important ecological repercussions.

  Determining the age of a mummy is rather easy, like finding a freshly killed bison. However, aging techniques are approximations. Northern mammals have an obligate period of dormancy during winter. All northern ungulates will not grow—cannot grow—even when ample food is present; they “turn off” growth for the winte
r. The horns and teeth leave an annulus of this period of dormancy, so the growth segments represent summer only. Thus on the basis of tooth and horn aging, it would probably have more meaning to speak in terms of an animal being so many summers old.

  There are five well-delimited growth zones (including the last, which makes up the proximal edge of the horn base) near the base, but annuli in the middle and distal parts of the horn are obscured, a common phenomenon even among living bison (Fuller 1959). Listed from the base distally these growth segments measure, on their dorsal surfaces, 22, 26, 35, and 46 mm, and a long 430 mm from the last segment until the distal tip. The tip is “broomed” somewhat, so there was an additional missing length beyond this. Judging from those measurements, and comparisons with horn sheaths of other Pleistocene bison, I estimated Blue Babe’s age to be 8 or 9 years. The large horns with their annuli are probably the best evidence that the bison is in the 8-year range. They assure us that Blue Babe is not a young six-year-old; nor is he a ten-year-old.

  Teeth cementum annuli can also be informative, but they too are approximate. When the bison was excavated the incisors fell out and were preserved. The first incisor (I1) was sent to a commercial tooth-sectioning laboratory in Montana. While not necessarily the best indicator tooth in bison, the first incisor was available before the bison had been rethawed and necropsied. This tooth erupts at about 2 years of age (Fuller 1959); bison do not normally lay down root annuli on the incisors until about 4 years of age (Navokowski 1965). The lab read the first incisor’s annuli as four; thus the annuli reading would make the bison about 8 years old.

  Among populations with the same rate of tooth wear, stage of wear can be a rough indicator of age. Fuller’s sample of 1,800 bison from Wood Buffalo Park showed that at age 8 the lower canine has more than 2 mm of wear. That tooth in Blue Babe appears to have at least 2 mm of wear, but not much more, which would place it at about 8 years of age according to Fuller’s sample.

  Skinner and Kaisen (1947) constructed wear stages of 1,322 mandibles from interior Alaskan Pleistocene sediments, including some from Pearl Creek. Blue Babe corresponds to S-2 in their diagram. At that stage the enamel of the first lower molar (Ml) is worn about halfway down its vertical height. Their measurements and mine on Alaskan material indicate that a bison from age 14 to 16 shows complete wear of the Ml enamel. Also their increase in mortality due to senility begins with age class S-3, which is to say that death from aging debilitation begins in bison at around 10 years of age. So age estimation (just prior to S-3) also points to the 7- to 9-year range.

  Epiphyses, which usually fuse in an age-related sequence, have been mapped for European bison (Bison bonasus) by Duffield (1973). He found that vertebral epiphyses fuse during the seventh year; during the eighth year those of the pelvis, ribs, and scapula fuse. All of the epiphyses of this mummy seem to be well fused, again suggesting it is at least 8 or 9 years old.

  At 8 to 9 years old Blue Babe would have been at his prime, having reached his maximum body size, social station, and fullest pelage development. In fact, his age is probably one notch past that point, just past the break in slope of the mortality curve, when older males begin to be lost from the population. In short, Blue Babe is a fine specimen of his ilk.

  5

  TRACKING DOWN BLUE BABE’S MISSING HUMP

  Hump shape may sound like an esoteric issue, but dorsal contours of different species relate in important ways to their behavior and ecology. Living bison and fossil Eurasian steppe bison all have subtly different hump shapes; I propose that this is because humps are a structural adaptation to the environments in which different bison groups live or lived. For this reason, I think that the hump shape of the Alaskan Pleistocene bison is significant and that it can be compared with humps of other bison for clues to behavior, locomotion, diet, and a whole suite of biological features. What sort of hump Blue Babe had is important.

  I was unable to reconstruct hump contour directly from the mummy because critical thoracic vertebrae were missing. There are, nevertheless, hundreds of fossil bison vertebrae from Alaskan deposits, and, although few of these have been dated, we know most bones are from the latest Pleistocene, well within radiocarbon-dating range (see dates listed for Alaskan Pleistocene bison in chapter 10). Because there was only one phylogenetic line of bison in Alaska during the late Pleistocene (Guthrie 1970, 1980), I argue that vertebrae and other postcranial material should be relatively similar, which is not to say that Pleistocene bison did not evolve. One would expect differences between bison living tens of thousands of years apart, but bison seem to exhibit a continuity of body shape within the late Pleistocene throughout Eurasia. Working on that assumption, I used bison vertebrae from other Alaskan late Pleistocene deposits to reconstruct Blue Babe’s hump profile. And although there were sexual and individual variations, the fossil bison vertebrae I examined followed a similar pattern.

  Girders and Gallops

  Most morphological, evolutionary, and systematic studies of bison are based on male skulls (e.g., Skinner and Kaisen 1947; Guthrie 1970; McDonald 1981). Thoracic vertebrae needed to reconstruct dorsal contours are among the most poorly preserved elements of fossil skeletons. Thoracic vertebrae are not conservative characters, and, taken singly, they are not very diagnostic. As a result, biologists and paleontologists have given hump shape little thought. Dorsal contour is actually the net outcome of a suite of physical features, including manes, bulging muscles, and connective tissue humps. But neural processes, or spines on vertebrae, are the key factor. Relative to body size, these rise higher in bison than in any other mammal, making a bison skeleton appear almost like the Permian reptile Dimetrodon.

  Functionally, an ungulate’s neural spines are comparable to the uprights in a suspension bridge. As in the Golden Gate Bridge in San Francisco Bay, truss members reaching skyward are attached to cables (tendons in the case of neural spines), which carry the long span between piers (legs) that reach to the bottom of the bay (fig. 5.1).

  In mammals this structure of uprights and cables does something more than provide a stationary support. Muscles combine with bones and tendons so that half the body can be cantilevered without leg support from the other end, like a cantilever bridge. This is exactly what happens in the gallop; the body is supported alternately from first the pectoral (front) end and then from the pelvic (rear) end. Although little is known about hump function, I can begin with the hypothesis that the most important role of shoulder humps is increasing the efficiency of the gallop. This role can be seen (1) as a cantilever for a phase of the gallop, (2) as a girder to aid in the length of foreleg stride, and, probably most important, (3) as a structure to add leverage, allowing an efficient use of the stretch tendon of the neck.

  At this point, to appreciate the function of hump shape we must approach it in a roundabout way, taking a close look at the physical demands of different gaits. The walk of a quadruped is analogous to two people walking in tandem, carrying a short pole across their shoulders, “out of step” with each other. A trot can be pictured as these same two people running, still out of step with one another. The advantage of a walk or trot is its efficiency. The body is always directly supported on both ends (anterior and posterior) and from alternate sides at the same time, so it does not tend to fall left or right. Because of the energetic efficiency of a trot, most quadrupeds use that gait at moderate speeds. Unlike an upright biped, a walking quadruped has to step twice over the same ground, once with the fore feet and once with the hind feet, which makes the gait easy to model with two bipeds walking in tandem. The main disadvantage of a walk or trot is that each stride, hind and front, must be the same length, just as two people carrying a pole on their shoulders should walk in cadence and have the same stride length. A quadruped’s hind foot cannot overstep the front foot in a walk or trot.

  Fig. 5.1. Hump engineering. The construction and action of neural spines have been likened to the upright trusses of a suspension bridge, but during the gallop they are, in
fact, part of a cantilever system. Weight is supported from below by forequarters or hindquarters, while the alternate end is held aloft by a cantilever effect. A strongly developed hump thus contributes to an efficient gallop, as seen in black wildebeest (pictured here) and bison.

  Camels and giraffes have developed a gait that avoids this problem but produces others. Instead of moving front and hind limbs out of step, they stride in step in a pace or rack. The problem with this gait is that the entire weight of the body is alternately thrown left and right, which is why camel riding can make a person seasick. The special build of a camel’s legs and its broad feet are accommodations to this inherent instability.

  Trotting is energetically efficient but has an inherent maximum speed limit. A trot cannot make full use of the flexible forelimb’s potentially greater stride length. As a trotting animal gains speed, the stretch of the front leg is limited by the stride length of the hind limb. Unlike the more freely attached forelegs, rear legs have a fixed radius, being securely anchored in the pelvic girdle. To gain greater speed an animal must shift into a canter or gallop.

  While a walk or trot can be modeled by two bipeds with a pole, and we can see that a walking or trotting quadruped does twice the work as two bipeds, it is not easy to model a gallop. To gallop our bipeds would have to alternately throw and pull each other forward by the pole while running. A gallop enables a small quadrupedal squirrel weighing a half kilogram to outrun an 80 kilogram bipedal human. A canter or gallop loses the support efficiency of a walk or a slow trot where the nonsupporting leg has only to move forward to catch the body as it falls. Canters and gallops are energetically more costly, in theory, because they have a greater vertical component, that is, the body is thrown into space, unsuspended, for substantial periods of the gait. However, a gallop has a different kind of efficiency because the hind and fore limbs do not duplicate each others’ work.