A Brief Look at the Evolution of Bison by Kathleen O’Neal Gear and W. Michael Gear

Below is a slightly more herbivores also increased. The Europe—like the Altamira cave detailed analysis of the more specialized and efficient site in Spain. evolutionary history of bison grazers and browsers became The Old World bison than the sketch we provided in larger-bodied, and developed population split into two our bison genetics article. more body hair and horns in groups: 1. A rare short-horned both sexes, perhaps to fight woodland wisent, Bison THE BOS FAMILY predators, or for sexual schoetensacki, and the large selection, probably both. Bison steppe wisent that we are all Bison and cattle have a evolved further north than any familiar with, Bison priscus. common ancestry that begins other Bovini genus and was B. priscus first reached around nine million years ago in obviously best adapted to the North America during the Europe with the appearance of colder temperatures of the late Mindel-Riss epoch, a global an animal called Parabos Pliocene and early Pleistocene. warming period that lasted from (Mammalia – Artiodactyla – Bos and Bison split 380,000 years ago to around Bovidae). The oldest Parabos approximately 2 million years 200,000 years ago. B. Priscus fossils are found in Spain, but ago. As the Pleistocene crossed the land bridge that there are also sites containing glaciers advanced around the connected Asia and North Parabos in Romania, America, known as Italy, Moldova, and the The reason Parabos is of interest to Beringia, and entered most recent evidence is what is today Alaska. found in Hungary, us is that around 4 million years ago B. Priscus survived in indicating that Parabos in China, it gave rise to Proleptobos, Alaska, Beringia, and survived until about 1.8 an animal that is the direct ancestor of parts of Canada until million years ago. around 12,000 years The reason Parabos is both Bos and Bison. ago, as documented of interest to us is that at the Old Crow around 4 million years ago in world (at its peak, about 30% of archaeological site in the China, it gave rise to the earth’s surface was covered Yukon. Proleptobos, an animal that is by glaciers), Bison adapted to There were two migrations the direct ancestor of both Bos the dramatically changing of B. Priscus from Beringia into and Bison. environments. Bison were North America. The first Bos-Bison branches from confined to the temperate zones during the Mindel-Riss period Proleptobos-Leptobos around of east Asia until after the gave rise to the giant-horned 2.2 million years ago and begins Donau glaciation, around bison, Bison latifrons. The rapidly radiating across Europe 550,000 years ago. By 450,000 second migration of B. Priscus and Asia. The climate was years ago they had spread into occurred during the late deteriorating, heading into the southeastern and central Sangamonian, another warm Pleistocene Ice Age, which Europe, and by the late Wurm period, around 130,000 years began about 1.8 million years glaciation (15,000 years ago) ago, and gave rise to Bison ago. As the forage quality they’d become common fossils, bison. B. latifrons survived diminished with the increasing as well as showing up in cave until around 21,000 years ago, cold, competition among large paintings throughout much of as dated from the Rainbow

1 © August, 2010, Kathleen O’Neal Gear and W. Michael Gear, all rights reserved Reprinted and posted online with written permission of the author

Ranch site in Idaho. Its Sheet and the Laurentide Ice 136,000 years ago because that extinction probably resulted Sheet, that finally met at the clade included all bison in from competition with B. bison Rocky Mountains and closed Shapiro’s study, many of which and from genetic swamping. the ice-free corridor, isolating were not modern bison but In an article in the journal, the bison south of the ice sheets. prehistoric species of bison. SCIENCE, entitled, “Rise and By 18,000 years ago bison in The best way to visualize this is Fall of the Beringian Steppe central North America were to imagine a family tree with Bison,” Beth Shapiro, et. al., sparse. The ice-free corridor many branches. The large using mitrochondrial DNA, opened again, as the glaciers branch that contains the discovered that the most recent melted back, around 14,000 ancestor from 136,000 years common ancestor (MRCA) of years ago, allowing bison to ago has smaller limbs growing all bison in their study lived move freely from Beringia into from it, one of which contains around 136, 000 years ago, North America until around the ancestor of all modern bison which “suggests that late 11,000 years ago, when dense and dates to between 22,000 to Pleistocene bison from the Ural spruce forests across Alberta 15,000 years ago. Mountains to northern China started to crowd out grasslands, Around 4,000 to 5,000 years are descendants of one or more and the development of ago, the Plains Bison, Bison dispersals from North peatland across western and bison bison, and the Wood America.” The article goes on northwestern Canada created Bison, Bison bison athabascae to say that several North new barriers to travel. evolved. Plains bison seem to American bison maternal Two subspecies evolved have evolved from B. bison lineages fall within the from Bison bison. 1. Bison antiquus. Wood Bison are more European clade (a clade is a bison antiquus and, 2. Bison difficult to access. Some branch on the family tree), bison occidentalis. Both researchers say that B b. which means that the traffic subspecies are found in the athabascae descends from B. b. didn’t just move one way. Great Bison Belt that extended occidentalis. Others say that Bison wandered back and forth from Alberta to Texas, and were Wood bison descended directly across Beringia from North hunted extensively by from B. b. bison. More research America to Asia for thousands PaleoIndian peoples, needs to be done to clarify this of years. particularly the Clovis and issue. Despite being a little From about 60,000 to 25,000 Folsom cultures. dated, the best article on this is years ago, bison were widely One of the most important found in the journal, GENOME distributed across Beringia and points that Shapiro, et. al., make (42: 483-496, 1999), and moved down an ice-free in their article is that “modern written by G.A Wilson and C. corridor along the face of the bison are descended from Strobeck, “Genetic Variation Rocky Mountains into central populations that were south of within and relatedness among North America. However, the ice before the LGM (the wood and plains bison between 22,000 to 18,000 years Last Glacial Maximum, 18,000 populations.” ago, the Ice Age reached its years ago), and that…all In the future, good DNA glacial maximum. At its worst, modern bison belong to a clade research will fill in more of the 18,000 years ago, three miles of distinct from Beringian bison. gaps in this family tree and ice covered Hudson Bay in This clade has a MRCA (most we’ll have a clearer idea of the Canada and the ice sheets crept recent common ancestor) details that led to the as far south as Illinois and Iowa. between 22 and 15 ky B.P.” development of modern bison. There were two massive This MRCA is different glaciers, the Cordilleran Ice from the ancestor that dates to 2 © August, 2010, Kathleen O’Neal Gear and W. Michael Gear, all rights reserved Reprinted and posted online with written permission of the author