SPHENOPHRYNE - American Museum of Natural History

2000 ZWEIFEL: PARTITION OF SPHENOPHRYNE
109
Fig. 66. Dorsal (upper) and ventral views of
skull of Sphenophryne cornuta, AMNH A92804;
scale bar measures 5 mm.
of Liophryne allisoni (fig. 70). Although ventromedial
thickening of the hyoid and the
protruding process evidently are not pertinent
at the level of specific and generic inquiry
here, this morphology may prove to be an
apomorphic state for the Microhylidae.
APPENDAGES
TERMINAL PHALANGES: The tips of the
bones may bear T-shaped expansions whose
span is more than twice the width of the base
of the bone, or at the other extreme the tip
may be bluntly rounded with only a slight
subterminal constriction, its width less than
that of the base. The relative breadths of the
fleshy terminal disc and that of the phalangeal
‘‘T’’ are closely correlated. The terminal
discs are discussed further under Body Form
and Proportions. The terminal phalanx of the
third finger, which generally shows the greatest
expansion of any of the hand’s digits, illustrates
the range of variation (fig. 71).
Among specimens of 20 species (one examined
by dissection), the span of the tip relative
to the length of the phalanx or to the
width of its base falls into one of three discrete
groups: (1) tip span/length of 0.24 and
0.32 in Oxydactyla alpestris and O. stenodactyla
(species with narrow, discless fingers);
(2) of 0.54–0.82 in 13 species known
or suspected to be litter-dwelling or surface
active species; and (3) of 1.09–1.36 in five
species of scansorial (Sphenophryne cornuta),
riparian (Austrochaperina palmipes, A.
rivularis, A. derongo, and A. basipalmata)
habits.
AXIAL SKELETON
PRESACRAL VERTEBRAE: There are invariably
eight nonimbricate presacrals, as described
for the Australian species (Zweifel,
1985b: 355). Variations in the transverse processes
include relative lengths and angular
orientation among vertebrae. For example, I
find relatively long processes on vertebrae 2–
4 and a strong anterior orientation to those
on vertebrae 7 and 8 in Austrochaperina derongo,
A. rivularis, A. pluvialis, and A. palmipes,
whereas in Oxydactyla stenodactyla
the processes are more similar in length and
more nearly at a right angle to the column.
Morphologies of the other species do not indicate
that a classification of discrete types is
possible.
SACRAL VERTEBRAE: The sacral vertebrae
are slightly to moderately expanded in most
species discussed here, more so in one or two
(figs. 72, 73). As an index of expansion I use
the ratio of broadest diapophyseal measurement
(anterior–posterior) to the span between
ends of left and right diapophyses, excluding
terminal cartilaginous extensions; a larger
number implies broader diapophyses.
Among 37 specimens of 19 species, including
three Australian endemics, this ratio