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

by Guthrie, R. Dale

  In other plains ungulate species (e.g., Oryx), where both sexes live most or all of the year in mixed herds, there is little marked sexual dimorphism (Estes 1974). Presumably, this sexual similarity is due to both sexes experiencing similar resource availability (fig. 6.2).

  In some situations (e.g., wildebeest and plains bison) large herds feed so intensively in one area that they keep grasses clipped short like a lawn. Grasses respond to this “mowing” by ungulates and reshoot laterally. The resulting lawn is highly productive and provides quality grazing, but with keen competition from other herd members. The main advantage to herding has to do with predation, not improved forage, although grass “lawns” can be maintained in highly productive condition by large herds and hence benefit individual animals. The antipredator advantages of herd life are usually accompanied by a decrease in forage quality. Ungulates select their food from an array of plants that are not equally desirable. The “cafeteria” selections in any one area differ in quality and digestibility, and less choice vegetation normally dominates. Single animals can afford to take the “cream,” but members of large herds must necessarily duplicate others’ routes and feed on second-choice plants or plant parts.

  Fig. 6.2. Ethology and sexual dimorphism. Competition for resources is the accepted explanation for radical sexual dimorphism in certain ungulate species. In a polygamous social structure, there is a selective premium for large, powerful bulls; dietary resources become the main limit on their body size and social paraphernalia. If males and females live more solitary lives, as do moose, sexual dimorphism is modest. Sexual dimorphism is most pronounced when females live in herds and males live a solitary life or exist in small herds, as do bison.

  American plains bison are flexible in their response to opportunities offered by different environments. Small bison herds are usually nonmigratory with marked fidelity to their home range. On such ranges the sexes live apart for most of the year. On the Great Plains, where bison herds built to enormous numbers, the entire herd was migratory for most of the year and sexes remained in proximity if not in the same subgroups. This phenomenon can be seen today in caribou. Small herds of caribou, numbering in the hundreds, are local and move little, whereas the long-distance migratory herds generally number in the tens of thousands.

  Thus we can look at sexual differences in social organs to learn something about the ecology and social behavior of extinct steppe bison. We know that sexual dimorphism is greatest among herd ungulates when adult males spend most of the growing season apart from the herd, foraging in small groups or solitarily. Today’s American male bison behave in this way. As bulls do not have to share resources with a large herd, they can select better-quality food, thus sustaining large body size.

  Sexual dimorphism in body size of B. priscus was great, greater in fact than that of any other bison species (McDonald 1981). While the mature bulls had a gigantic skull with long robust horns, the females were very gracile horned, with a skull more like that of cattle. Also steppe bison cows did not have heavy protruding eye orbits like males. The extreme sexual dimorphism of the steppe bison (fig. 6.3) suggests that (1) bulls remained separate from cows throughout the growth season, at least, and (2) herds of steppe bison may not have been so large as bison herds on the Great Plains. The Beringian steppe landscape probably favored moderate-sized groups of bison and a class hierarchy in an “open” social system oriented toward frequent display to many individually unrecognized herd members.

  Not only are male-to-female differences important in reconstructing social behavior, but so too are differences between adults and young. American plains bison differ from living European bison with regard to color of the young. The young of American bison (which normally live in large herds) are very light, contrasting with darker adults, while the young of European bison (a species that lives in small groups) are similar in color to their mothers: a medium monotone brown. This pattern conforms to the general rule that highly social species, living in open environments, generally have contrastingly colored young. This is true, for example, of baboons, wildebeest, reindeer, and others. Theoretically, the contrasting color gives the young special social distinction, protecting them from the full brunt of adult aggression. In large groups, individuals are often not known personally and must wear badges of rank, age, and sex.

  Paleolithic art is uninformative on the color of steppe bison calves (fig. 6.4), and we have, as yet, no mummified ones. I would expect, based on other plains-adapted features we have been able to reconstruct, that young steppe bison were light colored, in contrast to the dark adults.

  The size and shape of Blue Babe’s horns can also tell us about steppe bison behavior. Clutton-Brock and Harvey (1976) have proposed an association between larger horns (fighting and display paraphernalia) and environments where bulls can accumulate more females. Since extant bison have much smaller horns than steppe bison, their reproductive behaviors are probably different as well. I have used morphological features of fossil Beringian steppe bison to reconstruct their fighting behavior (Guthrie 1980): (1) Wound damage on the frontals indicates the animals received sharp forceful blows. (2) Moderately developed shock-absorbant front sinuses also indicate the use of frontal concussion blows. (3) The complex oval pattern on the horns of adult bulls makes it experimentally difficult to articulate the horns simply and smoothly with those of an opponent. (4) The rarity of broken horn tips in older males, compared with this occurrence in living bison, is striking. Most horn tips of older Beringian bison bulls are gracile and sharp. (5) Antitorsion fluting or louvering between horn sheath and core suggests substantial torsion in horn engagement during fighting. And (6) construction of thoracic suspension of the head points to an ability to exert great (lift) force upward.

  Fig. 6.3. Sexual dimorphism. Size and shape differences between sexes of plains ungulates are associated with the degree of separation of males and females throughout the year. Sexual dimorphism in skull size in steppe bison was extreme, suggesting that male and female steppe bison lived quite separately.

  Fig. 6.4. Calf-adult coat color differences. The young of ungulates living in large herds on open plains are usually distinctly colored; for example, plains bison calves are light reddish in contrast to the much darker adults. European bison in less open situations have young that are almost the same shade as adults. The color of young steppe bison is unknown.

  In early bison the horns were deflected backward or outward; eye orbits were telescoped, and the frontal sinuses were expanded. As bison evolved, these trends continued to increase in an irregular fashion. The element that links these changes in skull and horn morphology and makes them intelligible is a shift in fighting—from a more cattlelike, pushing of foreheads to the sharp impact of forehead clashing (fig. 6.5).

  Other ungulates have shifted to a clashing form of fighting; using the horn base as the contact surface. Sheep (Ovis) and goats (Capra) catch the leading edge of an opponent’s horns in the V of the inner horn crotch. In African buffalo (Syncerus) and musk-oxen (Ovibos) a flattened horn bos evolved as a catching or butting plate. Unlike the above animals, bison use the frontal bone as a clashing platform.

  Cattle engage their frontals and then push one another (Haféz 1975), while horns are interlocked. In the bison line this pushing or punching must have graded into violent butting and later into clashing. The horn cores, covered by a relatively thin horny sheath ending in a sharp tip, were adapted for “hooking” in the bovines. They were thus relatively fragile and susceptible to damage. The shift toward a more violent butting-clashing confrontation was apparently accompanied by a backward movement of the horns, moving them out of the way of the clashing plane.

  Associated with the above changes, the frontal sinus in bison expanded to a large-domed pneumatic cavity separated from the brain encasement by an elaborate strut complex (fig. 6.6). This cavity extended into both horn cores which are also hollow. The double wall separated by struts seems to have served as a bumper—a device to dis
perse and dampen the opponent’s blow away from the brain tissue (Schaffer and Reed 1972).

  In an earlier study (Guthrie 1980), I concluded that steppe bison displayed more and fought less violently than living plains bison and that horn size was a significant aspect of that display. Unlike the horns of living bison, those of steppe bison continued to grow longer even into old age, more like those of wild mountain sheep. Steppe bison horns are oriented forward. Horns of American plains bison are shorter and point upward. The smaller hair bonnet and the more forward-oriented long sharp horns suggest that the steppe bison “must have engaged from a close distance, with the horns slightly occluded diagonally but most of the pressure carried on the frontals, each trying to lift upward” (Guthrie 1980: 60).

  Fig. 6.5. Fighting style and anatomy. Bison and cattle are at opposite ends of bovine environmental adaptations and morphology. They fight in quite different ways: cattle hook and push; bison clash and push upward, lowering their hindquarters as a counterweight and using the shoulders as a fulcrum.

  Fig. 6.6. Cranial shock absorbers. Bison fight with their heads, clashing frontals against frontals, in violent concussions which create a dangerous shock to the brain. Bison skulls have a structure that reduces this shock by smoothing the transmission wave and by carrying the blow away from the brain. An intricate network of struts separates the inner and outer walls of the skull. Though appearing to be rigid, these flex on impact, absorbing some of the peak of the shock wave. The above drawing is taken from a naturally broken fossil steppe bison skull from the Fairbanks area. The brain is small, lying behind the convoluted olfactory “chestnut-appearing” structures in the lower medial portion of the skull.

  Soft tissue on the bison mummy supports information I collected from skeletons of other Beringian bison bulls which suggested that they fought frequently. Ubiquitous damage on the frontals and the antitorsion fluting (fig. 6.7) of the horn sheaths and cores suggest that Beringian bison engaged with considerable force (Guthrie 1980). However, the flattened-oval shape of the horn cross section and the frequency of sharp horn tips indicate a fighting mode unlike American plains bison.

  Modern plains bison bulls run full speed toward an opponent, clashing heads, with contact primarily on the parietals. The horns of American plains bison are blunted and broomed, and the large bonnet of hair serves as a shock-absorbing cushion for the head-on clash, which is followed by a head-to-head pushing contest.

  Fig. 6.7. Horns used in pushing versus clashing. The outer horns of steppe bison were supported by long, bony inner cores with deep flutes. This fluting helped bind the horn, locking it against twisting free during combat, and it suggests that a part of the steppe bison’s fighting technique was to engage horns, twisting and pushing the opponent in a bout of strength. The thick and heavy horns of sheep, African buffalo, and musk-oxen are used to absorb some of the clashing force of an opponent’s charge; in contrast, bison horns are relatively thin.

  The basic Bovini threat posture is a high head with chin pulled down (Sinclair 1977). Basic fighting technique is a head-to-head pushing contest. Among the Bovini, American plains bison and African buffalo are unique in that they clash. The former uses a clash prior to the pushing contest and the latter just clashes, like sheep; the pushing phase has been eliminated (Sinclair 1977). From clues present on steppe bison fossils, both bones and mummies, we know that they clashed, probably as a prefix to a typical Bovini head-push fight. This behavior has ties to the living bison of the American Great Plains and not to European bison, which have a poorly defined clash at best (Flerov 1977).

  The development of a full-blown, noninjurious head clash in American plains bison shifted emphasis from large horns to the upper forehead area (parietals) and led to the development of a padded-hair-bonnet clashing organ. Large horns of Pleistocene bison served to catch and hold an opponent while both pushed. The width of these sweeping horns essentially guaranteed protection from an aggressor slipping by to gore an opponent. By contrast, the short horns of plains bison allow an opponent to slip by, and wounds on the fore quarters after the rut are frequent (Petersburg 1973). I suggest that the forequarters of American plains bison have such a heavy coat of curly hair to act as a protective mantle.

  The shock-absorbing hair bonnet (fig. 6.8) in American plains bison is more appropriate for concussion, whereas thick skin on the face of the Alaskan bison mummy acts as a protective shield against horn puncture (fig. 6.9). These traits are correlated with horn size and shape differences in the two species, but they are more a difference of degree than of kind. Although Blue Babe did have facial hair padding, it was not as well developed as that of plains bison; likewise, while plains bison have thick skin on the face (Petersburg 1973), it is not as thick as Blue Babe’s. Beneath the facial skin of American bison is a thick layer of elastic connective tissue attached to the skull surface; no such material was found in Blue Babe.

  The mummy’s extremely thick frontal skin supports the idea that this was the area of primary contact; thick dermis acted as a shock absorber, dispersing energy over a wider area, and limited penetration of an opponent’s sharp horns. Another peculiar pattern in Blue Babe’s skin over the frontals is a network of ridges and folds (fig. 6.9). These also must have functioned as a unique shock absorber. Yet despite such heavy armor, some horn tips occasionally penetrated the skin and underlying skull roof. We know this because many bison skulls from Pleistocene sediments near Fairbanks have puncture wounds with healed bone growth on the periphery. Fighting between Beringian bison probably began with a hard punch from a standing position, followed by a pushing contest in which each bull tried to reach his opponent’s most vulnerable spots with his sharp horns.

  Fig. 6.8. Bonnet and horn variations related to fighting mode. Living bison species differ in their fighting style. Plains bison run at each other and clash head to head with great impact. European wisent are more like cattle, hooking horns and pushing from a fixed position. Steppe bison, like Blue Babe, probably used neither tactic; instead, their cranial anatomy and healed head wounds suggest clashing from a shorter distance, then pushing and wrestling for advantage.

  Fig. 6.9. Defensive skin armor over frontals. Blue Babe had strange folds in his thick forehead skin. (Right) A diagrammatic section of these folds shows the flat base on the dermis. These folds are not known to occur in living bison. American bison bulls (B. bison) have a thick, almost gelatinous, layer of connective tissue beneath the dermis in this area and farther out into the orbits and nasals.

  In the course of working with Blue Babe and other steppe bison fossils I have developed what I believe is a significant new insight about antler and horn use; this new theory applies not only to steppe bison but to the majority of antlered and horned ungulates. Our current understanding of horn and antler use has developed from models first proposed by Walther (1966) and Geist (1966), which seem fundamentally correct. Walther and Geist focused on the ritualized behavior that occurs prior to fighting, tracking through comparative ethology, and the evolutionary origins and forms of horn and antler displays. This emphasis on ritualization and displays influences their models of actual combat activity by deemphasizing its bloody nature and the damage-producing design of antler and horn weaponry.

  Walther and Geist proposed that early ungulate groups had stiletto horns and antlers and mainly attacked the opponent’s flanks, while standing facing opposite directions. The goal of fighting among these ungulates was apparently inflicting lethal abdominal punctures or debilitating damage of locomotor muscles. From this early stage, ungulates began to limit injury by catching and holding an opponent’s horns with their own, preventing access to more vulnerable body parts. Horns and antlers took on a more defensive design: lugs, hooks, and forks developed to more easily lock onto the other’s offensive weaponry. Geist (1966) proposed that the long arching hook of a bison’s horn is one of the first steps in this stage; the shape evolved to hook an opponent as it tried to get by the defensively padded head.

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sp; Once the level of defense reaches the point where rivals can seldom get by the more elaborately shielding horns or antlers to strike, fighting takes on a new form. Geist, Walther, and others argued that very social ungulates, instead of attempting to injure an opponent, first use ritualized displays to convince a rival of its lower rank; then, if equally matched, noninjurious but sometimes painful tests of skill and strength ensue. These formalized fights involve pushing or wrestling contests with locked horns or antlers; other phylogenetic lines have evolved a head-clashing technique. But all these fights accomplish the same thing: nondamaging combat which settles hierarchy disputes. Until recently this has also been my view, but now I think the emphasis on conventionalized combat formality is somewhat askew.

  The skew is consistent with the pervading mood of the late 1960s when our understanding of ritualized behavior in ethology first blossomed. Social signals, or expressive behaviors, as Walther called them, were seen as a means of ritualizing or conventionalizing agonistic behavior. This new awareness of formalized conventions for aggression largely supplanted the previous image of “nature red in tooth and claw.” Although theoretically independent from it, this ethological understanding emerged concurrently with the now discredited, but then popular, “epidectic display” (Wynne-Edwards 1962; proposal that many behaviors consisted of a rechanneling of violent, individually oriented competition toward ritualized resolution, for the best interests of the group). It is not too farfetched also to see ethological thinking of that time in the context of the counterculture peace movement in the United States. Remember, ecologists and ethologists (such as Paul Erhlich and Desmond Morris) played a prominent role in the newly developing generational Zeitgeist.