Posts Tagged ‘Bootherium bombifrons’

The Extinct Helmeted Musk-ox (Bootherium bombifrons) and Appalachian Grassy Balds during the Pleistocene

May 16, 2016

The tops of some mountains in the southern Appalachians are relatively treeless, resembling a man with a bald spot on his head, hence the name Appalachian bald.  There are 2 types of balds–grassy and heath.  Grassy balds are open environments surrounded by forests of red spruce, yellow birch, red oak, chestnut oak, and buckeye.  Heath balds consist of shrubby plants that prefer acid soils including rhododendron, azalea, and blueberry. Peter Weigl theorizes Appalachian balds are relic communities of ancient origin.  He believes harsh climates during Ice Age glacial maximums killed the trees growing at higher elevations in the southern Appalachians.  Prolonged sub-zero temperatures, frequent ice storms, and windy conditions increased tree mortality.  In some areas grass and in others shrubs took advantage of these sunny environments and became the dominant flora.  This attracted herds of megafauna such as mammoths, bison, and horses.  Their trampling and grazing further favored the dominance of grass and shrubs over trees.  Grass can withstand heavy grazing and rapidly grow back in this cool moist climate, while the toxic leaves of heath shrubs protected them from hungry megaherbivores.  Elk and bison continued grazing on the these mountain meadows until colonial times, keeping them open even as the climate became more favorable for tree growth, and then settlers brought their livestock to the balds  inadvertently maintaining these ancient landscapes.  But since the early 20th century when farmers switched to industrial jobs and stopped using the balds for livestock grazing, trees have been encroaching on them.  Some have disappeared completely, while others are in danger of being overgrown in forest.  Ecologists have recognized balds as unique natural communities and are attempting to save them with a combination of mowing and goat grazing.

Heading up towards Round Bald

Modern ecologists are using goats to help maintain grassy balds.  The helmeted musk-ox was closely related to goats.  I believe the helmeted musk-ox was the most important species of megafauna involved in the maintenance of grassy balds during the Pleistocene.

Peter Weigl notes several lines of evidence supporting his belief that southern Appalachian balds are ancient natural communities originating early during the Pleistocene or before.  There are many endemic species of  plants growing on balds that are found nowhere else.  The process of evolution is slow and it’s unlikely so many different species would have evolved so rapidly.  There are also many disjunct species found more commonly in more northerly latitudes.  They are relics surviving in higher cooler elevations but were once more widespread in the region when overall climates were cooler.  This means these plants have been present here throughout many changes in climate.  There’s no evidence of fire in these cool moist higher elevations, and few fire-adapted species of plants live here. This rules out anthropogenic fire as a mechanism in bald creation. Balds were described before Europeans settled here, and even as late as 1790 only 80 settlers lived in the region–not enough people to have cleared so much land.  Relic and endemic species of small mammals, birds, reptiles, and amphibians are also evidence of ancient origin.  Finally, without regular mowing and grazing, these open environments are converting to forest, suggesting a dependence on megafauna presence.

The Canadian blackberry (Rubus canadensis) is native to high elevations in the southern Appalachians, but it has become a problematic plant on grassy balds.  This plant will encroach on grassy areas, completely taking over.  Trees begin to sprout in the brier patches–the first stage of succession leading to the termination of a grassy bald.  Ecologists use goats (Capra aegagrus) to knock back the Canadian blackberry because they readily feed upon the thorny plants.  Goats are closely related to the extinct helmeted musk-ox.  Upon considering this relationship and the coincidental use of goats in bald maintenance, it occurred to me that the helmeted musk-ox may have been the single most important species of megafauna responsible for the existence of Appalachian balds.  Along with caribou (Rangifer tarandus) and flat-headed peccaries (Platygonnus compressus), they were probably the first large mammals to colonize the higher elevations during the harshest climatic phases of the Ice Ages.  Caribou could survive on lichen, while musk-oxen and flat-headed peccaries could subsist on tougher vegetation.  From fossil coprolites scientists know this species of musk-oxen ate woody vegetation during long winters.  They were hardier than bison, horses, and mammoths.  I think these latter 3 species didn’t move to higher elevation balds until warmer phases of climate.  Though they aren’t picky eaters, they prefer lush grasses over thorny blackberry vines.  It was the musk-oxen and perhaps the flat-headed peccary that consumed the thorny vines which would otherwise eventually crowd out grasses here.

Image result for Bootherium bombifrons

Life size model of the helmeted musk-ox.  This species lived as far south as Louisiana.  I’m not sure how accurate this model is.  Helmeted musk-oxen were taller and less wooly than the extant species of musk-ox. 

Rare endemic species such as the Gray’s lily are evidence that Appalachian grassy balds are of ancient origin.

Fossil evidence of the helmeted musk-ox has yet to be found near the present day location of Appalachian balds.  They may never be found here because the most common fossil sites in this region are caves, and musk-oxen probably didn’t venture into caves where they could get ambushed by predators.  However, bones of this species have been dredged from 2 sites off the coast of North Carolina.  Individual musk-oxen bones have turned up on a North Carolina beach and in a stone quarry near the coast as well.  Skeletal evidence of musk-ox as far south as Louisiana and Mississippi has also been reported.  A line drawn on a map between these far separate locations goes right through the southern Appalachians, so it’s a safe assumption their range included this region, and I’m convinced they played an important role in the origin of grassy balds.

Reference:

Weigl, Peter; and Travis Knowles

“Temperate Mountain Grasslands: A Climate-Herbivore Hypothesis for Origins and Persistence”

Biological Reviews 89 (2) 2013

Musk-oxen are More Closely Related to Goats than They are to Cows

January 29, 2014

In one of the first articles I ever wrote for this blog, I speculated there were 3 species of Pleistocene bovines roaming the area known today as Georgia.  Bison antiquus, a late Pleistocene species of bison, is thought to have evolved from Bison latifrons about 24,000 years BP, yet  a specimen of the latter found in Clark Quarry near Brunswick, Georgia suggested there was a temporal overlap between these 2 species. This specimen  was originally dated to 14,000 BP.  Since I wrote that article, scientists have resubmitted this specimen to radiocarbon dating. and this time it produced a date of 24,000 BP–within the accepted time span this species is thought to have existed.  It’s still one of the more recent specimens of this species, but it is not evidence of temporal  overlap with B. antiquus. There was never more than 1 species of bison living in the region at the same time.

About a month ago, a reader also alerted me to an error I made by classifying the helmeted musk-ox (Bootherium bombifrons) as a bovine.  I wrongly assumed because of its appearance, and the common name ox, that it was closely related to cows. An oxen is a word used for a castrated cow. I should have paid closer attention to my mammalogy books.  Musk-oxen are more closely related to goats and sheep than they are to cattle.  Many laymen likely share my misconception, so I’ve reviewed the literature and will now sort out the bovids.

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Woolly musk-oxen are like a really large goat and are not close kin to cattle.  A species of musk-oxen adapted to temperate climates  lived as far south as Louisiana during the Iice Age.  It was taller, had shorter hair, and a different horn structure than the species  still extant.

Photo: A mountain goat sitting on top of a mountain

Mountain goats are in the same subfamily as muskoxen.

Saiga antelope are also in the same subfamily as musk-oxen.  During the Ice Age saiga antelope lived as far east as Alaska.
The Bovidae family is divided into 2 subfamilies: the caprinae and the bovinae.  Bovids originated in Africa and most species are adapted to warmer climates, but during the Pleistocene a number of species became adapted to the cooler climates of the Ice Ages, and they spread throughout northern Eurasia and across the Bering Landbridge to North America.  None ever made it to South America.
Pleistocene and modern American species in the caprinae subfamily include saiga antelope (Saiga tatarica), shrub oxen (Eucatherium sp.), mountain goats (Oreamnos americanus), Harrington’s mountain goat (Oreamnos harringtoni), bighorn sheep (Ovis Canadensis), dall sheep (Ovis dalli), woolly musk-oxen (Ovibos moschantus), and the helmeted musk-oxen (Bootherium bombifrons)..  The  bovinae species that colonized North America were bison (Bison sp.), and the yak (Bos grunniens), the latter having been restricted to mountains in Alaska during some climate stages of the Pleistocene.
Saiga antelopes still occur on central Asian steppes, but they expanded their range to the grassy mammoth steppe of Alaska during the Last Glacial Maximum.  Shrub oxen were probably the first bovids to colonize North America early during the Pleistocene, and they didn’t become extinct til about 11,000 BP.  Shrub oxen are not known to have occurred east of Iowa.  Harrington’s mountain goat was a sister species of the modern day mountain goat and is also now extinct.
The only species of caprinae that ever colonized southeastern North America was the helmeted musk-ox.  Fossils of this species have been found in Texas, Lousiana, Mississippi, western Tennessee, and Virginia; but notably not in the abundant fossil deposits of Florida. (See https://markgelbart.wordpress.com/2011/07/27/the-south-central-salient-of-the-helmeted-musk-ox-ovibos-cavifrons-or-bootherium-bombifrons/ )  This suggests the southeasternmost range limit was in north or central Georgia or possibly South Carolina’s piedmont.  The helmeted musk-ox expanded its range during the Last Glacial Maximum when grassy desert scrub habitat became a widespread type of environment throughout North America.  Fossil coprolites, originally excreted by helmeted musk-oxen, show these tough animals fed upon green vegetation during summer but could subsist on dry twigs during the long cold Ice Age winters.  Like their goat cousins, they could absorb nutritional value from dead plant material, reminding one of the cartoon stereotype of goats eating the wrappers off tin cans. This amazing animal was able to extract nutrition from cellulose.
Because helmeted musk-oxen were able to survive on dry twigs, I do not believe climate change could have caused their extinction.  There has never been a shortage of dry twigs in North America during any climate phase.  I do believe the replacement of their favored habitat of desert scrub and grassland with forests and woodlands following the end of the Ice Age did cause the range of this species to contract.  This range contraction made them more vulnerable to human overhunting.  Like wooly musk-oxen, the helmeted musk-ox formed defensive circles when confronted with predators.  This was effective against wolves or saber-tooth cats but disastrous against spear-wielding humans who could slaughter an entire herd at once from a safe distance.  R. Dale Guthrie speculated competition with bison caused the extinction of helmeted  musk-oxen, but I reject this hypothesis because these 2 species co-existed for 300,000 years.  I believe bison avoided extinction because they run away from people and migrate long distances and perchance found regions where the population of humans was too low to eat them faster than they could reproduce.