These grazing beasts of North America are some of the most imposing and majestic animals in nature. Researchers stated that it had survived for over two million years before the first humans appeared on the planet. The iconic Bison which was voted as the national mammal of the United States of America has evolved over the years. This is the fascinating story of the evolution of the largest land mammals in North America.
Scientists state that the bovine family (called Bovini) was divided into two groups about 10 million years ago. These were the buffalos (specifically called the Syncerus and Bubalus), and the other group contained taurine cattle and Bison.
Over time, the family that contained the taurine cattle and Bison appeared to mingle with other species, but the evolution continued. This crossbreeding is believed to have led to the line that gave rise to the yak, which has a relationship with the Bison.
In 2003, researchers looking into the deoxyribonucleic acid (better known as DNA) extracted from mitochondria concluded that there were four unique lines in the Bovini tribe, and these were listed as follow:
- Yak and American Bison
- Zebu and taurine cattle
- European Bison
- Tembadau, gayal, and gaur
But a more in-depth study of the Y chromosome showed a clear link between the American Bison and its European counterpart. The Bison group broke away from the line that led to cattle (Bos primigenius) during the Plio-Pleistocene period around five million years ago in an area that is now South Asia.
Six extinct species and two extant ones have been listed. Out of the six species that went into extinction, five did so during the Quaternary extinction event. Three of these five species include Bison occidentalis, Bison latifrons (this was the most extensive and heaviest bison species to have inhabited North America where it existed for around 200,000 years), and Bison antiquus, all endemic to North America.
A fourth species called the Bison priscus (also known as steppe bison) was found in places like East Asia, Central Asia, and Western Europe. The fifth lived in the forests of Eurasia and was called Bison schoetensacki (the woodland bison).
A sixth species, Bison palaeosinensis, which was evolving in South Asia in the Early Pleistocene era is believed to be the Bison Priscus’s evolutionary ancestor and all the Bison lines that followed. The Bison Priscus (steppe bison) evolved from Bison palaeosinensis in the Early Pleistocene era, and some fossils show how it appeared two million years ago.
Steppe bison fanned out in various parts of Eurasia, leading to more lines. It would become extinct in Siberia around 6000 BCE and at about 5400 BCE in Alaska. There have been several ancient cave paintings of the Bison in southern France and Spain, and they all depicted the extinct steppe bison.
It is believed that the modern European Bison evolved from the steppe bison. There is no clear fossil evidence linking the European Bison with the steppe bison but researchers are still trying to work out the precise evolution lines.
At a point down the evolutionary tree, steppe bison became involved in crossbreeding with the ancestors of what is now the yak of today. After this crossbreeding, the population of steppe bison crossed the Bering Land Bridge and reached the North American continent.
Evidence sourced by researchers is clear regarding the crossings of the Bison to and from Asia around half a million years ago, and it is believed this continued until about 220,000 years ago. The steppe bison kept fanning out across different parts of North America and Eurasia, where it existed until about 10,000 years ago.
Bison antiques would later become a replacement of the Bison latifrons. This happened in North America about 250,000 years ago. It eventually evolved into Bison occidentalis and later the relatively smaller Bison bison (which is the modern American Bison) around 10,000 years ago. Even though the European and American bison share similarities, they are some behavioral and physical differences. The Bison has remained resilient after its survival for well over two million years.