Whatever its exact history, the trend of the time was to envision social evolution as generally culminating in noninjurious agonistic forms. We saw the horn and antler structures of more social ungulate species as devices to hold an opponent, thus converting potentially deadly fights into noninjurious tests of strength. Evolution had transferred the spearheads of early horns and antlers into a multitude of shielding shapes that were now used in ritualized dances of aggression and dominance.
I realize now that the spearheads are still there, mounted on the shield itself. And they are there because they are in active use. I propose that the horns and antlers of most social species consist of two main portions: a defensive apparatus, as defined by Geist (1966), and other structures specifically formed to breach this same defense—to inflict as much damage as possible given the effective defenses. The offensive aspects of horn and antler form are structured to injure a rival by reaching (1) through, such as with the oryx’s long, sharp horns, (2) under, for example, with the long, upward-hooking brow and bez tines of the wapiti, (3) over, such as with the high, upward-reaching antlers of reindeer and caribou, and (4) around, as in the widely hooked horns of steppe bison.
During my sabbatical year in Africa, I watched a fighting gemsbok (Oryx) reach through the horns of a rival and thrust his long rapiers with total energy, obviously intent on skewering the other male, who responded with (sometimes incompletely successful) parries. I examined freshly shot older impala males, just after rut, with deep gouges in their head and neck, their ears in fringes from violent tears. Living in Alaska, I have watched dozens of caribou rutting battles, both in the flesh and on film; these are not just formalized pushing battles but are in deadly earnest. Those long beams reach over and catch an opponent’s strained shoulder and neck muscles between inwardly pointing tines and, like giant claws, dig and scratch, hair tufts flying, with the full weight of the body thrown into every gouge. I think the majority of horned and antlered ungulates that lock head to head have in their armory specially adapted offensive structures used to injure their rivals by breaching his defenses.
This behavior and horn structure I had watched in African antelope and saw afresh in Alaskan ungulates caused me to rethink the image of fighting behavior I had reconstructed for steppe bison. Two important pieces of evidence from Alaskan fossil steppe bison show that the male’s long, widely arching, hooked horn had an offensive role—to cause injury. One was the frequent skull damage seen in Pleistocene bison bulls from a sharp-pointed “instrument,” undoubtedly another bull’s horns, and the second was the unusually thick neck skin noted in Blue Babe, which dispersed the pressure of the pointed horn tip and thus decreased its damage. Steppe bison horns were not horns for clean wrestling, but were used to protect the animal while at the same time allowing him to reach around the opponent’s defenses and stab the dickens out of him.
I propose that steppe bison horns work this way: The broad forward-facing cross section of the horn’s trunk, discussed previously, acted as a defensive blocking device, engaging the corresponding portion of an opponent’s horns, above or below his horns, or in an offset rotation with one above and one below (fig. 6.10). The slightly flattened trunk of the horn reached well out, away from the skull, and would have added leverage to keep an opponent from swinging around to the side. The rough annuli on the forward surface probably assisted the defensive holding process. Occasionally, the broad, telescoped orbits of these bison may also have helped hold an opponent’s head from rotating. The occiput of steppe bison is especially broad from left to right (fig. 6.10), providing more leverage to hold the skull from a lateral twist. The bison’s fighting strategy must have been to keep parallel to his own body the sharp forward-pointing horntips of an opponent. As long as the animals were standing horn to horn on a line, the match was a “draw,” that is, the fight was stalemated. In a serious fight, one bison would try to push the other backward faster than it could retreat and still keep its body in alignment. The greater strength of one bison would thus cause the body of the other to rotate while their heads remained locked and held rigid. This would have protected the body of the advancing bison, while the twisted neck and shoulders of the retreating bison would be within range of the advancing bison’s sharp horns (fig. 6.11).
Fig. 6.10. Pattern of horn engagement. The horn and head structures of Blue Babe and other steppe bison show that their horns engaged well away from the face. This holding structure would have added leverage to keep an opponent from swinging around to the side.
The inward curve of horn tips found among many fossil specimens can be better explained by this strategy than as a hooking device to keep opponents from slipping by. An inward-pointing hook decreases the angle an opponent’s body must rotate before horns can be dug into his neck. When bison had their heads lowered and horns locked in place, the taut neck and shoulder muscles would not be far from the inwardly pointing horn tips (fig. 6.10).
When two bulls with the same-sized and -shaped horns twist symmetrically, their horns contact each other’s neck at the same time and to the same degree. If one animal has a significantly longer outward reach of the horn trunk, or a longer forward-pointing horn tip, it will cause proportionally greater damage (fig. 6.11). This is probably one of the selective forces that created the long and sharply pointed hooked horns in steppe bison.
Fig. 6.11. Horn shape and defense breaching strategy. The widely arching sharp horns of steppe bison were curved so that they could reach through an opponent’s defense and puncture the opponent’s neck or shoulder. The scapula shown, UA-V-54803, was punctured all the way through by a horn stab and has healed.
I propose that evidence of horn shape, preserved skeletal wounds on fossil steppe bison skulls, and Blue Babe’s thick protective head and neck skin suggest that the hooked shape of steppe bison horns functioned as a breaching device. Once locked with the opponent’s horns, this form allowed the stronger bison with the larger horns to ultimately breach or circumvent his opponent’s holding defenses by reaching around and stabbing into his body.
For steppe bison the initial display of social stature would have been concentrated more toward the anterior body than it is now in European bison. The length of the tail characterizes this difference: Blue Babe’s tail is only half the length of the European bison’s, both living (B. bonasus) and extinct (judging from cave art). A long tail can be used to express emotion if the opponent is watching the entire body. Among the European B. priscus, the height of the neural spines, hence hump, was larger and extended more posteriorly than that in B. bison (Poplin 1984). Also, this posterior hump had contrastingly colored hair (Geist 1971b; Guthrie 1980). As I showed in the last chapter, Alaskan steppe bison were similar to European Pleistocene bison in hump shape. Likewise, the beard was relatively short, but the ventral mane running down onto the sternum was moderately well developed. Yet display paraphernalia of steppe bison in Paleolithic art are not as cephalized as in plains bison. The latter has an enlarged head bonnet and elongated beard. Foreleg pantaloons also add mass to the anterior end of plains bison, B. bison bison, as part of their exceptionally developed anterior display. Plains bison swing these pantaloons in their threat displays, exaggerating the movements of the forelegs (Petersburg 1973; Lott 1974).
Fig. 6.12. Steppe bison horns as an antipredator device. African buffalo and muskoxen have a sharp hook on their horns which seems to be used primarily against predators and has little or no role in interactions within the species, unlike bison.
Compared to living plains bison, the focus of display among steppe bison was subtly more posterior. The darker peripheral coloration of Alaskan steppe bison would have focused an opponent’s attention toward the center of the body, but perhaps farther forward than with Pleistocene and Holocene European bison. However, unlike all living bison, Pleistocene bison had massive horns, which no doubt formed a central part of their social display.
Unlike Holocene bison, which had no predator larger than wolves, steppe b
ison faced lions (Panthera leo) and other large predators. Their horns, therefore, were not only a social organ, but also a major antipredator defense. Like musk-oxen (Ovibos moschatus) and African buffalo (Syncerus cafer), steppe bison had horns with sharply hooked tips, propelled by massive neck and shoulder muscles; the horns were potentially lethal to even the largest predator (fig. 6.12). The fact that a lion killed Blue Babe is further testament to the different environmental pressures experienced by Pleistocene and living bison.
7
STEPPE BISON ECOLOGY AND PHYLOGENY
The Character of Steppe Bison
Steppe bison such as Blue Babe were one of the most common large mammals across the north during the Pleistocene. From western Europe to the Yukon Territory, for over a hundred thousand years, bison, mammoths, horses, reindeer, and others occupied a biome of locally diverse habitats. Soviet scientists refer to these animals as the “mammoth fauna” (Flerov 1977; Vereshchagin 1959; Sher 1971). I have expanded this designation and used the name Mammoth Steppe (Guthrie 1980, 1982, 1985), including both plants and animals in my discussions. I think Mammoth Steppe fairly describes the continued presence of these key grazing species over a truly vast geographic range and chronologic depth.
Mammoths (Mammuthus), horses (Equus), and bison (Bison) were the “big three” of the Mammoth Steppe (Guthrie 1982). We know that each of these species was a grazing specialist, but how and why they were such a successful team is not completely clear. Vereshchagin and Baryshnikov (1982) and I (Guthrie 1982) have proposed theoretical specializations that would have accommodated this association. We know from contemporary studies that large bovines, equids, and proboscidians tolerate different degrees of fiber in their diets. This was undoubtedly true of Pleistocene bison, horses, and mammoths, and it is likely that other specializations existed as well. Perhaps each species retained specializations that let them tolerate the others’ presence despite changes with time and geography. This would not necessarily exclude evolutionary change in themselves or in other species in the community. If fact, all underwent marked evolutionary changes, particularly in the latter part of the Pleistocene. Horses increased and then diminished in size, from giants to petite ponies (Sher 1971). Mammoths also changed, particularly with regard to cheek-tooth complexity (Sher 1971), to the extent that some paleontologists have wanted to give the later mammoth separate generic stature. Bison changed too. Bison fossils record changes in horn core size and shape and subsequent cranial effects (Guthrie 1980).
The large-horned steppe bison found in western Beringia (Flerov 1977, 1979; Sher 1971; Vereshchagin and Baryshnikov 1982) and eastern Beringia (Guthrie 1970, 1980) are interpreted as chronological representatives of the same species. McDonald (1981) separated Beringian fossil bison into two phylogenetically separate species and proposed that these alternated in appearance during interglacials and glacials throughout the Pleistocene. But this seems to be a misinterpretation of the data (Walker and Boyce 1984). Rather, Beringian fossil bison seem to be one variable species; such variation within a species is comparable to that found today among reindeer-caribou (Rangifer tarandus). Morphological differences between northern steppe bison and bison farther south, as well as changes in steppe bison over time, probably represent adaptive tuning within the context of the far north and events there. At least this would be a logical start in accounting for changes within Bison priscus—its similarity to and differences from other bison. I use these different specific names for bison groups, knowing that in reality they are all closely related and are better thought of as one species complex.
We know that during much of the last hundred thousand years Beringia has been herbaceous steppe (Hopkins et al. 1982). Such conditions would have favored grazing species. During most of this time we can document the presence of bison in Alaska and, in fact, know that bison were the dominant large mammal (Guthrie 1968). A comparison of equids, proboscidians, and bison remains from central Alaska showed that bison were overall the most numerus and especially predominated in the uplands (Guthrie 1968). My observations since that time have supported those earlier studies. Among the large numbers of Pleistocene bones collected at Pearl Creek, where Blue Babe was found, over 80% are from bison. These include stratigraphically dated bison bones from the interstadial and undated fossils emerging from all other parts of the section.
In Alaska, dozens of male steppe bison skulls have been collected which still have the entire horny sheath attached to the horn cores. At least the proximal annuli are very marked, unlike many living bison, and some sense can be gained as to life expectancy and perhaps maximum life span. I have plotted age against length around the outside horn curve (fig. 7.1). Although the sample is too small for a precise look at survivorship, we can conclude that steppe bison had a life expectancy similar to that of American plains bison.
Fig. 7.1. Cumulative length of male Alaskan steppe bison horns. Bison horns grow only during the summer, leaving an annulus, a construction between the segments of summer growth. Among bovids the first summer’s segment is often worn away, so this was not measured. The cumulative lengths of horns from eight Alaskan fossil steppe bison are shown for comparison with Blue Babe. The first three annular rings are not visible in Blue Babe’s horns, but the plots of later annuli show its growth rate is in the lower range of this sample. These plots show that maximum horn length is reached at 8 or 9 years (Blue Babe’s age). Variations in individual horn lengths seem to depend mainly on growth rate of the early segments.
Diet of Steppe Bison
We can determine what Blue Babe ate, or more generally, what steppe bison ate, by looking at diets of extant bison and examining the anatomy of fossil bison. Extant bison are eclectic foragers. Yet despite this apparent versatility, bison are actually adaptive specialists and prefer low-growth herbs, particularly grasses (Guthrie 1980, 1982). I think this was also true for steppe bison (Bison priscus). Vereshchagin and Baryshnikov (1982) have argued on the basis of hypsodont molars and cochleariform incisors that the steppe bison was a grazer. Gut contents of a steppe bison mummy from the Siberian Kolyma Basin were analyzed, along with pollen from surrounding sediments, by Korobkov and Filin (1982). All plant macrofossils they found in the gut were grasses, and pollen showed a predominance of Graminae, Compositae, Chenopodiaceae, and Cruciferae. Anatomically and physiologically modern bison are grazing specialists (Hofman and Stewart 1972). They consume some forbs and woody browse, but browse seems to be their lowest choice (Soper 1941). Grass comprises 80% to 90% of the diet of American plains bison studied under natural conditions (Meagher 1971, Peden et al. 1974; Hansen 1976; Hubbard and Hansen 1976; Hansen, Clark, and Lawhorn 1977; Olsen and Hansen 1977; Vavra and Sneva 1978; Van Vuren 1984). However, at the margins of their range or on poor range they can subsist on other plants. For example, bison in Wood Buffalo Park rely on sedges. European bison now confined to atypical dense woodland habitats consume a lot of browse (Borowski, Kra, and Milkowski 1967).
Bison, which were introduced to Alaska in the 1930s, provide an interesting sample. There are several populations; all are confined to windswept riverine areas within or adjacent to mountain passes where wind keeps snow cover to a minimum depth, allowing the bison to reach winter food. Campbell and Hinkes (1983) found that the Fairwell bison eat grasses and sedges through the winter (browse contributed to just over 1% of the bison’s diet). Bison in the Delta herd take some browse and Equisetum but mainly eat riverbar grasses and farmer’s barley (Gipson and McKendrick 1981). Two smaller herds at Chitna and the Copper River are on very poor range (Miquelle 1985). There are about fifty bison in the Chitna herd, and they consume considerable summer browse, about 50% willow and 50% graminoids (based on five fecal droppings that were analyzed). The winter diet was about 75% browse and the rest graminoids (from a sample of four droppings).
I use this dietary information (see table 1) from living northern bison to address two issues. The first is an argument used by some ecologists—that if bison can survive today in A
laskan boreal forests on browse, their presence in the fossil record cannot be taken to indicate a steppe environment (Colinvaux and West 1984). However, steppe bison are only part of a large community of grazers. The inability of reintroduced bison to spread from small special habitats argues, if anything, against their adaptive ability to cope in the north without widespread graminoids. I return to this point later in the context of arguments against the Mammoth Steppe.
During the time I’ve spent thinking about Blue Babe and writing this book, I’ve also been working on several other projects which turned out to be relevant to the Blue Babe study. In one of these I investigated the diets of Mammoth Steppe fauna by picking small plant fragments from the infundibula of teeth in fossil skulls (fig. 7.2). In part this work was a response to proposals that the dominant Mammoth Steppe animals—bison, horses, mammoths, saigas, and others—were not grazers at all but simply ate sedges or willow as moose, caribou, and musk-oxen do today. Fossil steppe bison skulls were especially numerous from the Fairbanks mining district, and I was able to get plant fragments from these bison as well as from other fossil herbivore teeth. Plant fragments taken from the molars were sent to one of two laboratories that now do most histological plant identifications for range managers and wildlife biologists. Biologists and range managers rely on these two labs to identify plant fragments in fecal samples. The waxy cuticles covering the plant epidermis are especially resistant to digestive enzymes and acids, and these cuticles pass through the gut undamaged. Except for a slight etching, the cuticles can be readily identified in the lab. Plant cuticles carry an imprint of the underlying epidermal cell pattern. This pattern is characteristic of each plant group, even more so than pollen coats. In fact, pollen is undiagnostic for many plant groups, especially grasses and dicot forbs, whereas cuticles are quite diagnostic. An animal’s diet can thus be approximated by this kind of laboratory look at plant remains in their feces. This approach is less laborious than trying to follow an animal at close range, observing every bite; often observations are simply impossible. It is difficult to get close enough to wild animals, and even when rather tame they can be difficult to study. For example, many deer feed mainly at night.
Frozen Fauna of the Mammoth Steppe: The Story of Blue Babe Page 17