|Abstract or Summary
- Dicamptodon is the single, extant genus of the
ambystomatid subfamily Dicamptodontinae. Two species, D.
ensatus (Eschscholtz) and D. copei Nussbaum are recognized.
D. ensatus is found in the forested, mountain regions of
northwestern California and western Oregon, in the Willapa
Hills and Cascade Mountains of Washington, in extreme
southwestern British Columbia, and in the northern and
central Rocky Mountains of Idaho. D. copei is found in
the Olympic Mountains, Willapa Hills and southwestern
Cascades of Washington; and in the vicinity of the
Columbia River Gorge in extreme northwestern Oregon. The
two species are sympatric in the Columbia River Gorge,
southern Willapa Hills, and southwestern Cascades of
The two species differ, among other characters, in
blood serum proteins, sensitivity to thyroxine, mode of
life history, body size, relative head size, limb length,
tail height, tooth number, gill raker number, color, and
degree of ossification of skeletal elements.
Geographic variation is prominent in D. ensatus.
Multivariate analysis of morphometric characters of larval
populations discriminates three groups: a Rocky Mountain
Group, a Cascade and Oregon Coast Range Group, and a
Californian Group. The first two groups seem to be more
similar to each other than either is to the Californian
Group. The Californian Group can be divided into a
southern subgroup and a northern subgroup; and the northern
subgroup can be further separated into a coastal subgroup
and an interior highlands subgroup. These groups are all
more-or-less verified by analysis of color of larvae and
adults, and morphometric characters of adults.
These groups correspond geographically with major
features of topography in the Pacific Northwest. The
California Group is confined south of the geologically
old and complex Klamath-Siskiyou Mountains. The southern
Californian subgroup is found south of the "North Coast
Divide", and the northern subgroup is found north of this Divide in an area of northwestern drainage. The interior
highlands subgroup of the northern Californian subgroup
is found in the higher, summer-dry mountains of northern
California where the substrate is complex and of a
different origin than the coastal substrate. Strong
morphoclines occur across the Klamath-Siskiyou Region
into southwestern Oregon. The Rocky Mountain Group is
separated from the Cascade and Oregon Coast Range Group
by the broad, arid Columbia Plateau.
Variation is slight over the relatively small range
of D. copei, and what variation exists seems to be a
function of geographic distance.
The dicamptodontines have been an evolutionarily
conservative group confined to the humid temperate,
Arcto-Tertiary environments of western North America
throughout their Cretaceous and Tertiary history. A
remnant of the once wide-spread, ancestral habitat occurs
today in the humid fog belt of northwestern California
and southwestern Oregon. D. ensatus living in this area
today exhibit the most primitive features of all living
Dicamptodon. These include: large heads, long limbs and
tails, many teeth and gill rakers, propensity to
transform, and perhaps the habit of vocalizing as a
terrestrial, defensive adaptation.
D. copei is viewed as a relatively recent derivitive
of an ensatus-like ancestor. This ancestor is believed to
have had a propensity for neoteny and body attenuation
associated with life in the extreme climatic, physical,
and biotic environments imposed by Pleistocene glaciation.
Isolation in western Washington during a glacial maximum
allowed these tendencies, along with small body size, to
be selected for, unhampered by gene flow from outside
populations. It is thought that the ensatus-like
ancestor of D. copei was more similar to recent northern
populations of D. ensatus than to recent Californian
populations of D. ensatus. Californian populations
were relatively unaffected by Pleistocene climatic
extremes, as they passed this period in the milder,
ancestral environment of southern, coastal latitudes.
During the last glacial maximum, the Rocky Mountain
populations were probably continuous with populations on
the lower eastern slopes of the Washington Cascades, via
a connecting, wet, forested parkland, which existed south
of the Cordilleran ice sheet in north-central Washington.
This parkland was broken up after the ice retreated, during
the Altithermal interval, about 7-4,000 years ago, and it was at this time that the Rocky Mountain Group became
Postglacial readjustments in the ranges of D. copei
and D. ensatus account for their current narrow zone of
Subspecies of D. ensatus and D. copei are not