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IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 191HISTORICAL PERSPECTIVES

The short-headed gartersnake has had a stormy taxonomic
history. Originally described by Cope in 1892 from

Franklin, Venago County, Pennsylvania, the name brachystoma
was suppressed by Ruthven (1908), who, while noting that he
lacked sufficient specimens to reach any position of certainty,

considered it to be a synonym for Thamnophis butleri (Cope)
1889. Albert G. Smith reviewed the butleri complex in 1945
and decided that two distinct species were recognizable. For the
more eastern of these he resurrected Cope’s name brachystoma.

Conclusions
Application of Fisher’s “t” test to comparable sets of data from
butleri and brachystoma demonstrates conclusively that the two
constitute separate populations. The question as to whether they
be two discrete species, or merely two races of a single species
having discontinuous ranges is a moot point. It is clear that two
races of one single species can exist with definite gaps separating
their geographical ranges. Indeed, if our present concept of the
mechanics of speciation is correct, it is inescapable that such a

The Northwestern Garter Snake (Thamnophis ordinoides; top) and the Western Terrestrial Garter Snake (Thamnophis elegans; bottom) are two
species of garter snakes that share the relatively small eyes of Butler’s Garter Snake. However, their distribution and a suite of other dissenting char-
acters preclude any assumptions of close relationships, suggesting that small eyes evolved independently in these lineages.

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A Statistical Study of Thamnophis 
brachystoma (Cope) with Comments on 

the Kinship of T. butleri (Cope)5

A. J. Barton

5 Extracted from Barton (1956. Proceedings of the Biological Society of
Washington 69: 71–82).

Iguana 14.3 b&w text  7/28/07  9:57 PM  Page 191



condition must sometimes exist. During the long period of time
following the isolation of one segment of a population from oth-
ers of its kind, while the gradual accumulation of changes in its
genetic pattern is developing to the point where they are great
enough to render it a recognizably distinct species, that popula-
tion must of necessity belong to the species from which it has
been isolated. The position of the final point of departure in
such a situation, that point where the isolated population ceases
to be conspecific with the parent stock, depends ultimately upon
a subjective evaluation by the reviewer, colored by his own
species concept. While caution must be exercised in the erection
and continued recognition of species, it seem advisable in the
absence of concrete contrary evidence to allow the present prac-
tice of regarding butleri and brachystoma as distinct species to
continue unchanged.

192 IGUANA  •  VOLUME 14, NUMBER 3  •  SEPTEMBER 2007 BARTON

The Shorthead Garter Snake (Thamnophis brachystoma) is another
species that was historically confused with Butler’s Garter Snake. A. J.
Barton’s short note clearly showed them to be distinct at the species level. 

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Editor’s Remarks

These two perspectives illustrate nicely the ongoing
uncertainty and evolving definition of what consti-

tutes a species (for non-technical reviews, see Powell. 2004.
Species and subspecies: What do they mean and why
should we care? Iguana 11: 108–113 and 2002.
Understanding animal classification. Iguana Times 9:
18–26). At the time of Stejneger’s article (1895), the scien-
tific community was still adjusting to a classification based
on relationships rather than mere similarities in appearance,
although today’s taxonomists still rely extensively on
anatomical features. By the time of Barton’s study (1956),
the transition in philosophy had been completed, only to
be replaced by disputes over varying applications of differ-
ent species concepts. Our understanding of evolution and
the role of DNA was still tentative (the structure of the
molecule had been described only in 1953), and this
remains an ongoing issue. However, the disagreements
regarding the utility and relevance of different concepts of
what a species is, which occasionally descend into lively
debates, mean nothing to the organisms themselves. Still,
the labels serve science and humanity by allowing us to
identify groups of organisms in order to facilitate commu-

nication and to better understand evolutionary relation-
ships and the complexities of nature.

That the subject of the selected pieces is Butler’s
Garter Snake (Thamnophis butleri) is no accident. This
small snake (maximum known total length = 737 mm) not
only serves as an effective illustration of the ever-changing
nature of classification, but, in addition, has recently been
the focus of a political controversy regarding the protected
status of disjunct populations in Wisconsin (see Aprill.
2007. Iguana 14: 94–99). Using modern tools, studies of
the Wisconsin populations may yet reveal them to repre-
sent a species distinct from T. butleri in the rest of the
species’ currently defined range, which extends from cen-
tral Ohio and Indiana north through eastern Michigan and
the extreme southern tip of Ontario. From a biological per-
spective, genetically unique populations deserve the same
consideration by conservationists as recognized species.
However, protection of the latter is certainly easier to jus-
tify to politicians, who may know little and care less about
biology, but do understand the popular appeal of organ-
isms — even snakes — found nowhere else but in their
state.

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