Related Biomes
Helmeted Muskox
Helmeted muskox, Bootherium bombifrons
The helmeted muskox, also known as Harlan's muskox or the woodland muskox, is an extinct species of muskox that lived in the U.S. Midwest during the late Pleistocene. This species was native to North America, and evolved at some point during the middle to late Pleistocene in the intermontane valleys of eastern Beringia (Campos et al. 2010). The scientific classification of Bootherium bombifrons has a long and complex history. Until recently, paleontologists thought that at least two different types of helmeted muskoxen were present in late Pleistocene North America. One type had smaller, more slender horns with a rounder cross-section; this form was originally classified as Bos bombifrons, and later as Bootherium bombifrons, based on a specimen recovered from Big Bone Lick, KY in 1809. The second type had larger, heavier horns with an oval cross-section, and it was originally classified as Bootherium cavifrons, and then later as Symbos cavifrons, based on a specimen recovered from Oklahoma in 1852. More recently, it has been demonstrated that these two forms represent the male and female of a single species (McDonald and Ray, 1989), and since Bootherium bombifrons was described first, this classification has been kept for the species. New aDNA research has demonstrated conclusively that the helmeted muskox was genetically different than the extant muskox, Ovibos moschatus (Campos et al. 2010). These findings agree with previous morphological studies, which highlight the differences in body shape and size of the two species as well as the distinct differences in the size and shape of their horns.
Helmeted muskox (Bootherium bombifrons) skeleton on display at the Indiana State Museum in Indianapolis.
Height: unknown
Weight: 423.5 kg (934 lb); Mendoza et al. 2006
Physical Description:
The helmeted muskox was taller and less robust than the tundra muskox, with longer legs, a shorter, lighter, more gracile body, and less protruding eye orbits (Guthrie 1992). It had a long, deep skull, which, in males has a roughly pitted, basined surface between the horn cores. The horn cores were located high on the skull and curved outwards and downwards. The mummified remains of a subadult female, discovered by gold miners in Alaska in the 1940s, provided a unique opportunity to study the preserved soft tissues of this extinct species (Lent 2000; McDonald 1984). These studies demonstrate that Bootherium had a shorter, lighter coat with much shorter, finer guard hairs than are found in the living muskox, and a significantly longer tail, characteristics that indicate less emphasis on body heat conservation.
Bootherium bombifrons have been recovered from a wide range of habitats, including a variety of grasslands, alpine meadows and woodlands, and they have been found in association with a disperse range of animals, including tree squirrels, open-habitat voles, caribou, and extinct stag-moose (Cervalces), suggesting that Bootherium moved between boreal forests and open areas. Compared with the barren, tundra habitats occupied by the extant species of muskox (Ovibos), the nature of the presumed habitats utilized by Bootherium indicates that this animal was adapted to slightly warmer climates than the extant muskox. This is supported by the relatively higher frequency of Bootherium in Beringian sites dated to warmer interglacial periods than those dated to cooler glacial periods.
Based on a number of studies, Bootherium appears to have been a generalist herbivore. A study of preserved plant materials recovered from the molars of six different Bootherium skulls from Alaska, combined with the examination of preserved fecal pellets associated with a 40,000 year old Bootherium skeleton, indicates that this species consumed both grasses and woody plants (Guthrie 1992). In particular, this study revealed that these animals browsed on woody plant bark, various upland grasses, willows, and large amounts of Vaccinium, an ericaceous shrub. This dietary reconstruction is expanded on by a bone chemistry study of Bootherium specimens recovered from Beringian sites, which produced δ13C and δ15N values suggestive of a dietary focus on sedges and lichens (Fox Dobbs et al. 2008). These researchers concluded that Bootherium likely foraged for sedges in wetter lowland areas and browsed on lichens within open tundra habitats.
The longer, more gracile legs of this animal, combined with their shorter pelage, suggest that it was more mobile than the living muskox. Higher mobility would suggest different social interactions, habitat use and responses to threats than their more sedentary cousins (Guthrie 1992). These animals may have been more migratory in their habitat use, seeking better protected landscapes and better sources of food in winter. Higher mobility likely resulted in more frequent encounters with new individuals, which may have affected their social interactions, particularly during the rutting period. The structure of the male's skull and horns suggest that they established dominance during rut by running clashes, as with modern muskox, but that the force of the clash was confined to the horn bos - the flattened, boney plate across the top of the skull, between the horn cores. Furthermore, the morphology of the male horns suggests that they were used primarily for clashing, rather than for defense from predators. Female horns, on the other hand, were likely used for antipredator defense.
Of the fours species of muskox that have inhabited North America, the helmeted muskox appears to have been the most abundant and widely distributed. This animal has been recovered from sites ranging from Alaska and Yukon to Texas, and from California to the Continental shelf off the coast of New Jersey.
As with many other large mammals in North America, the helmeted muskox went extinct during the terminal Pleistocene. One compelling argument put forward for its demise is that climate-driven changes in vegetation during this transitional period created habitat loss for Bootherium across much of its range and forced it into direct competition with better adapted species, such as bison and moose (Guthrie 1992).
Helmeted muskox remains are relatively common throughout the midwestern U.S. In fact, the type specimen for this species was recovered from Big Bone Lick, KY on an expedition sent by Thomas Jefferson in 1807. Remains of this animal have been recovered from numerous sites throughout Indiana, Illinois, Michigan, and to a lesser extent, Missouri, Iowa, Minnesota, and Ohio.
- The common name for this species, helmeted muskox, derives from the helmet-like boney plate that covers the animal's skull.
Campos, P., Sher, A., Mead, J., Tikhonov, A., Buckley, M., Collins, M., Willerslev, E., Gilbert, M. T. P. 2010. Clarification of the taxonomic relationship of the extant and extinct ovibovids, Ovibos, Praeovibos, Euceratherium and Bootherium. Quaternary Science Reviews 29: 2123-2130.
Fox-Dobbs, K, Leonard, J., Koch, P. 2008. Pleistocene megafauna from eastern Beringia: Paleoecological and paleoenvironmental interpretations of stable carbon and nitrogen isotope and radiocarbon records. Palaeogeography, Palaeoclimatology, Palaeoecology 261: 30–46
Guthrie, R. D. 1992. New paleoecological and paleoethological information on the extinct helmeted muskoxen from Alaska. Annalog Zoology Fennici 28: 175- 186.
Lent, P. 2000. Muskoxen and their hunters: a history. University of Oklahoma Press.
McDonald, J. N. 1984: An extinct muskox mummy from near Fairbanks, Alaska: a progress report. Biological Papers. University of Alaska 4: 148- 152.
McDonald, J.N., Ray, C.E. 1989. The autochthonous North American musk oxen Bootherium, Symbos, and Gidleya (Mammalia: Artiodactyla: Bovidae). Smithsonian Contributions to Paleobiology, 66.
M. Mendoza, C., Janis, C. M., Palmqvist, P. 2006. Estimating the body mass of extinct ungulates: a study on the use of multiple regression. Journal of Zoology 270(1):90-101.
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