American Bison - Buffalo Field Campaign

Phenotype: Observable physical or biochemical
characteristics of an organism. Phenotype
is determined by both genetic makeup and
environmental influences.
Clade: A biological group (taxa) that share features
inherited from a common ancestor.
Holocene: A geological period, which began
approximately 11,550 calendar years B.P. (about
9600 BC) and continues to the present. It has been
identified with MIS 1 and can be considered an
interglacial in the current ice age.
Phylogenetics: The study of evolutionary relatedness
among groups of organisms.
Glacial maximum: The time of maximum extent of
the ice sheets during the last glaciation (the Würm
or Wisconsin glaciation), approximately 20,000
years ago.
Taphonomic processes: The transition of the
remains, parts, or products of organisms in soil, e.g.
the creation of fossil assemblages through burial.
Taxonomy: The science of classification of
organisms. Nomenclature is the system of naming
organisms in relation to their phylogeny.
Bison moved south into the grasslands of central North America
when the ice sheets retreated at the beginning of the Sangamon
Interglacial (MIS 5e) 130,000-75,000 years B.P. (MacDonald
1981), evolving there into a large form, B. latifrons. This giant
bison possessed a horn span of more than two metres and
was abundant in the central continent during the Sangamon
Interglacial. It underwent a gradual reduction in body size and
horn span (Guthrie 1980; van Zyll de Jong 1993). During the
subsequent Wisconsin Glaciation (110,000-12,000 years B.P.;
MIS 2-4 and 5a-d), Beringian and southern populations became
separated as the Laurentide continental ice sheet extended
into western Canada from 20,000-13,000 years B.P. (Burns
1996; Wilson 1996). Geographic separation had profound
biological, taxonomic, and evolutionary effects. Southern bison
evolved into distinctive phenotypes (van Zyll de Jong 1993) and
separate mtDNA clades. All modern American bison now belong
to a single clade that is distinct from Beringean bison, with a
most recent common ancestor between 22,000 and15,000
years B.P. (Shapiro et al. 2004). This interpretation is consistent
6 American Bison: Status Survey and Conservation Guidelines 2010
with complete separation between northern and southern
populations at the time of the last glacial maximum (20,000-
18,000 years B.P.).
Data presented by Shapiro et al. (2004) and Wilson et al. (2008)
support the hypothesis that modern bison are descended
from populations that occurred south of the ice sheet before
the Last Glacial Maximum. Southern bison underwent rapid
in situ evolution during the early Holocene from B. antiquus to
an intermediate form B. occidentalis, then to the modern form
B. bison (Wilson et al. 2008). When the continental ice sheets
began to melt, bison invaded the emerging ice-free corridor
from the south where thawing and melting occurred first.
Colonisation from Beringia was limited (Shapiro et al. 2004).
Overlap between northern and southern bison occurred in the
vicinity of the Peace River in north-eastern British Columbia
where northern bison were present by 11,200-10,200 years B.P.
(Shapiro et al. 2004), and southern forms of bison were present
10,500 years B.P. Molecular research by Shapiro et al. (2004)
indicates that all modern bison are descended from populations
living south of the ice sheet before the Last Glacial Maximum.
The two modern North American subspecies (plains bison and
wood bison) diverged by about 5,000 years ago (Gates et al.
2001; van Zyll de Jong 1986). The wood bison (B.b. athabascae)
was the most recent variant to occur in Alaska, the Yukon and
Northwest Territories and the plains bison (B.b. bison) is the
most recent southern variant of the North American species
(van Zyll de Jong 1993 Stephenson et al. 2001). Small-horned
bison similar to wood bison also occurred in northern Eurasia
during the Holocene (Flerov 1979; Lazarev et al. 1998; van Zyll
de Jong 1986, 1993). Although the European bison (B. bonasus)
is morphologically similar to and readily interbreeds with the
American bison, they form distinctly different clades based on
mtDNA sequences of the 273 bp-long fragment of cytochrome
b gene (Prusak et al. 2004). This is consistent with geographic
separation between these two species starting during the mid-
Pleistocene and before reverse-dispersal occurred from North
America to Siberia.
2.2 Original Range
Previous typologies divide the Holocene range of bison into
“prehistoric” and “historic” periods (van Zyll de Jong 1986).
The distinction between them is not based on objective or
biologically meaningful criteria, and provides an artificial and
confusing temporal dichotomy that persists despite well-
informed arguments to the contrary (Stephenson et al. 2001).
A preferred and more accurate alternative is to refer to the
previous range of bison as “original” range, thereby avoiding
the necessity to distinguish between written records and
other sources including zooarchaeological evidence and orally
transmitted knowledge (Gates et al. 2001).