In México and northern Central America approximately 55 species
of eleutherodactyline frogs (Eleutherodactylus, Syrrhophus, and
Tomodactylus) are known. Four genera can be recognized on the
basis of the nature of inguinal glands, morphology of the hands and
feet, and certain osteological features.
Fig. 1. Tomodactylus angustidigitorum (UMMZ 114305, × 4.5) illustrating
the lumbo-inguinal gland typical of members of the genus. From a kodachrome
by Wm. E. Duellman.
Leptodactylids have a variety of glands that have been used as
generic characters. Smith and Taylor (1948) regarded the so-called
inguinal gland as a generic character in Mexican eleutherodaycty-lines.
Lynch (1965) showed that Eleutherodactylus and Microbatrachylus
cannot be separated by the nature of the gland or the
condition of the prevomers (dentate or not). Syrrhophus and Tomodactylus,
as defined by Smith and Taylor (1948), are not generically
distinct because of overlap in the condition of the prevomers and in
the development of the gland. Firschein (1954) stated that Syrrhophus
differed from Tomodactylus by having an axillary gland,
but it is now known that one species of Syrrhophus lacks the gland.
The inguinal glands of Eleutherodactylus and Syrrhophus, if present,
are diffuse, irregular in outline, and generally not prominent;
in Tomodactylus the gland is higher on the body (a lumbo-inguinal
gland), compact, oval in outline, and prominent (Fig. 1). Axillary
glands occur in most Syrrhophus but are not known in Tomodactylus
or Eleutherodactylus.
The tips of the digits are laterally expanded in most Eleutherodactylus,
Syrrhophus, and Tomodactylus. Two species of Eleutherodactylus
(augusti and tarahumarensis) and two Tomodactylus (angustidigitorum
and grandis) lack any expansion of the digital tips.
All but two of the species of eleutherodactyline frogs (E. augusti
and E. tarahumarensis) have a transverse groove across the tips of
the digits (Fig. 2).
Fig. 2. Palmar views of the hands and lateral views of the tip of the third
digits of Eleutherodactylus alfredi (left, KU 93994, × 5) and Hylactophryne
augusti (right, KU 102594, × 3).
Supernumerary tubercles rarely are present on the feet of Eleutherodactylus,
but are present and numerous in every species of
Syrrhophus, Tomodactylus, and in the members of the augusti group
of Eleutherodactylus (Fig. 3). The tubercles are small and numerous
in Syrrhophus and larger in Tomodactylus and the Eleutherodactylus
augusti group. Most species of Eleutherodactylus have no
plantar supernumerary tubercles; a few species have such tubercles,
which never extend between the metatarsal tubercles as in Syrrhophus
and Tomodactylus.
Fig. 3. Plantar views of feet of Eleutherodactylus alfredi (left, KU 93994,
× 4.5), Syrrhophus pipilans nebulosus (middle, KU 58900, × 7.5), and Hylactophryne
augusti (right, KU 102594, × 3) showing differences in size and
arrangement of supernumerary tubercles.
Tarsal folds and tubercles are lacking in Syrrhophus, Tomodactylus,
and the augusti group of Eleutherodactylus. Several species of
Eleutherodactylus lack tarsal folds and tubercles, but in nearly
every species group, one or more species possess either an inner
tarsal fold, inner tarsal tubercle(s), or outer tarsal tubercles.
The terminal phalanges of Syrrhophus, Tomodactylus, and all
Eleutherodactylus (except the frogs of the augusti group) are distinctly
T-shaped. In the latter, the bones are knob-shaped distally
(Fig. 4). T-shaped terminal phalanges also are present in Lithodytes
and Trachyphrynus but not in other leptodactylid genera. At
least one species of Eupsophus (E. quixensis) has terminal phalanges
that resemble those of the Eleutherodactylus augusti group.
Several species of Eleutherodactylus, Syrrhophus, and Tomodactylus
with slender fingers have T-shaped terminal phalanges although the
terminal dilations proportionately are only scarcely wider than the
finger tips in the Eleutherodactylus augusti group. The presence of
a terminal groove at the tip of the finger is an external indicator of
the T-shaped terminal phalanges.
Fig. 4. Terminal phalanges of four leptodactylid frogs (all × 13.5). (a)
Eleutherodactylus mexicanus, KU 55593; (b) Eupsophus roseus, KU 84731;
(c) Eupsophus quixensis, UIMNH 59643; and (d) Hylactophryne augusti,
KU 56192.
All Mexican eleutherodactyline frogs have quadratojugal-maxillary
articulations, completely roofed skulls in adults, median contact of
the nasals, separated occipital condyles, and large prevomers. The
premaxillae of all species are visible when the skulls are viewed from
directly above. The pterygoid lacks a medioventral flange and does
not meet the palatine. In no species is the anterior arm of the
squamosal in contact with the maxillary. Of the numerous species
examined (30 Eleutherodactylus, four Syrrhophus, and four Tomodactylus),
the species in the Eleutherodactylus augusti group are
unique in having a sphenethmoid with a blunt anterior edge.
All species have large cartilaginous plates in the pectoral girdles;
none possesses a bony style. No divergent modifications of the
clavicle and coracoid bones are known in the family.
