SPHENOPHRYNE - American Museum of Natural History

94 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 253
paucity of the description and poor condition
of the juvenile holotype, Microbatrachus
pusillus cannot be identified with any known
BODY FORM AND PROPORTIONS
SEXUAL DIMORPHISM: Typically the sexes
cannot be distinguished externally. The male
subgular vocal sac is not evident except
when the frog is calling. The only male external
secondary sexual character, found in a
some species of Austrochaperina, is a tendency
for an elongation of the snout that is
paler than the dorsal surface of the head. Females
grow slightly larger than males. In 25
species the largest males average 90% of the
SVL of the largest females, (range 81–
100%). In only one species with an adequate
sample (i.e. Liophryne allisoni) are the largest
male and female of equal size.
HANDS AND FEET: Hands range in size
from about 19% to 27% of SVL. Smaller
hands appear to be associated with secretive
or burrowing habits, whereas scansorial species
are at the high end of the range.
Relative sizes of feet in different species
range more widely than do those of hands,
from about 33% to 51% of SVL. As would
be expected, the burrowing and litter-dwelling
species fall at the lower end of the range,
roughly 40% of SVL, whereas species
known to be active on the forest floor have
the relatively longest feet. The lengths, both
relative and absolute, of the tibia and foot
(and presumably other leg segments not measured)
are typically similar, but some exceptions
are notable.
The relative finger lengths are the same in
all species: 3 4 2 1. The first finger
is typically long; only in Sphenophryne cornuta
is it conspicuously reduced (fig. 52).
The toe lengths of all species show no variation
from the presumably primitive order 4
3 5 2 1, and most are webless.
Only one species, Austrochaperina palmipes,
has moderately webbed toes (fig. 56D), while
one other, A. basipalmata, has basal webbing
(fig. 56C). A slight trace of webbing appears
in some A. derongo.
The fingertips and toe tips may be narrow
MORPHOLOGY
genus and species, and that future taxonomic
stability will be enhanced if the name is set
aside as a nomen dubium.
and rounded with no trace of expansion or
of terminal grooves, or they may be broadened
into adhesive organs up to more than
twice the width of the penultimate phalanx
and with a prominent terminal groove, or any
degree in between (figs. 49, 51). Intermediate
conditions include discs present on toes but
not on fingers, but never the reverse, or discs
on toes and longer fingers only. The adhesive
pad cells of one species, Austrochaperina derongo
(fig. 50), are perhaps more similar to
the cuboidal cells of terrestrial Liophryne
rhododactyla (Green and Simon, 1986: fig.
8) than to those of scansorial Cophixalus riparius
(Green and Simon, 1986: fig. 9).
Most species have discs on fingers and
toes, typically with those of the toes being
distinctly larger. For comparative purposes I
use the discs on the third finger and fourth
toe, which normally are the largest. Two species,
S. cornuta and A. palmipes, have the
largest finger discs. In S. cornuta the finger
disc is markedly wider than the toe disc by
about 1.2. The finger disc of A. palmipes
is virtually the same size (relative to body
size) as that of S. cornuta, but in contrast the
toe disc is also large, usually almost equal to
the finger disc.
There is a clear correlation between the
state of the digital tips and habits. The species
with the largest discs (and most pronounced
T-shaped terminal phalanges; see
Osteology) are, so far as their habits are
known, scansorial: S. cornuta climbs into
shrubs or low into trees when active at night;
A. basipalmata, A. palmipes, A. rivularis,
and A. macrorhyncha are riparian forms with
need for adaptation to traversing slick, sometimes
steep rock surfaces. Those species with
small to intermediate degrees of expansion
are terrestrial, active on and within the leaf
litter and in some cases doing limited climbing.
The narrow, rounded tips seen in Oxydactyla
alpestris and O. stenodactyla are associated
with a burrowing mode of life.
Most species have subarticular elevations