University of Kansas Publications

Museum of Natural History



Volume 17, No. 11, pp. 503-515, 5 figs.

March 20, 1968

Genera of Leptodactylid Frogs in México

BY


JOHN D. LYNCH



University of Kansas

Lawrence

1968

University of Kansas Publications, Museum of Natural History



Editors: E. Raymond Hall, Chairman, Henry S. Fitch,

Frank B. Cross





Volume 17, No. 11, pp. 503-515, 5 figs.

Published March 20, 1968





University of Kansas

Lawrence, Kansas





PRINTED BY

ROBERT R. (BOB) SANDERS, STATE PRINTER

TOPEKA, KANSAS

1968



31-9418

[Pg 505]

Genera of Leptodactylid Frogs in México

BY JOHN D. LYNCH

INTRODUCTION

According to the most recent review of the Mexican amphibian
fauna (Smith and Taylor, 1948), six genera of leptodactylid frogs
occur in México. One other genus, Pleurodema, occurs in Lower
Central America. Smith and Taylor recognized one species of Engystomops,
28 of Eleutherodactylus, three of Leptodactylus, eight of
Microbatrachylus, 12 of Syrrhophus, and five of Tomodactylus. Subsequent
to the publication of their checklist of the Mexican amphibia
(1948), numerous taxonomic changes have been proposed. Many
species of Eleutherodactylus have been added to the fauna, either
through the extension of their recorded ranges into México from
Guatemala or by the recognition of species unknown in 1948,
whereas some nominal species have been synonymized. Microbatrachylus
has been regarded as synonymous with Eleutherodactylus
(Lynch, 1965); four species of Microbatrachylus currently are
regarded as valid (Duellman, 1961, Lynch, 1965). Syrrhophus was
revised in part by Duellman (1958) and Firschein (1954), and a
species of Tomodactylus transferred to Syrrhophus by Dixon (1957),
who redefined Tomodactylus and added more species to the genus.

Since beginning my studies of the Mexican leptodactylids in 1962,
I have become acutely aware of difficulties involved in defining the
genera. A revision of Eleutherodactylus and a review of Syrrhophus
are nearing completion, but prior to their publication it is desirable
to redefine the genera of the Mexican leptodactylids, and in so doing
recognize an heretofore unnamed genus. The definitions of Eleutherodactylus
and Leptodactylus may need to be altered in the future,
since both are widespread in South America and occur in the
West Indies. Their definitions as given here are as precise as
present knowledge permits. Syrrhophus and Tomodactylus are
small assemblages that occur only in southwestern United States,
México, and Guatemala.

Taylor (1952) synonymized Engystomops with Eupemphix which,
although related, should be regarded as generically distinct (Gallardo,
1965). Perhaps the most conservative classification is that of
Myers (1962) who, without published evidence, combined Eleutherodactylus,[Pg 506]
Syrrhophus, and the South American Lithodytes in a
single genus.

The major problem for students working with the Mexican leptodactylids
has not been the separation of Engystomops or Leptodactylus
from other genera but the separation and definition of the
eleutherodactyline frogs currently placed in three genera, Eleutherodactylus,
Syrrhophus, and Tomodactylus. As will be shown in this
paper, these are more conveniently placed in four genera. Once a
fourth genus is recognized, certain phylogenetic problems disappear
and a reasonable zoogeographic interpretation is possible for Middle
American leptodactylid distribution.

ANALYSIS OF CHARACTERS

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.

Glands

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[Pg 507]
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.

Hands and feet

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).

[Pg 508]

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[Pg 509]
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.

Skull

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.

[Pg 510]

Pectoral Girdle

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.

GENERIC ACCOUNTS

Genus Eleutherodactylus Dumeril and Bibron, 1841

Genus Engystomops Jiménez de la Espada, 1872

[Pg 511]

Genus Hylactophryne new genus

Genus Leptodactylus Fitzinger, 1826

[Pg 512]

Genus Syrrhophus Cope, 1878

Genus Tomodactylus Günther, 1900

DISCUSSION

The preceding definitions only slightly alter the present generic
limits of Mexican leptodactylids. Two species, previously regarded
as Eleutherodactylus, are transferred to the new genus Hylactophryne.[Pg 513]
The arrangement of the species of Syrrhophus and Tomodactylus
remains the same as concluded by Dixon (1957), Duellman
(1958), and Firschein (1954) in their reviews of the genera.

Lumbo-inguinal glands are most prominent in the genera Pleurodema
and Tomodactylus. Various nondescript glands are present
in many genera, but none is so well developed as those of Pleurodema
and Tomodactylus.

At least nine leptodactylid genera are either known or thought to
be terrestrial breeders lacking a free-living tadpole stage (Eleutherodactylus,
Euparkerella, Hylactophryne, Niceforonia, Noblella,
Sminthillus, Syrrhophus, Tomodactylus and Trachyphrynus). Niceforonia
and Trachyphrynus, and probably Hylactophryne, are not
closely related to the other genera. Direct development probably
is an adaptation to adverse environmental conditions since many of
the species occur in semi-arid or cold (Andean páramos) areas.
Eleutherodactylus is generally thought to be the stock from which
Euparkerella, Noblella, and Sminthillus evolved (Griffiths, 1959)
and from which Syrrhophus and Tomodactylus are derived (Firschein,
1954).

The present distribution of Hylactophryne (isolated on the Mexican
Plateau) and its digital form (like that of Papuan and many
primitive South American leptodactylids) suggest that the genus
was isolated in México throughout the Tertiary, whereas the other
Central American genera are either post-Pliocene derivatives of
Eleutherodactylus or invaders of Central America from South America
since the mid-Pliocene land bridge was formed (Lloyd, 1963).

Piatt (1934) presented arguments against assigning Eleutherodactylus
latrans to the genus Lithodytes and concluded that it was a
"true" Eleutherodactylus. Contrary to his arguments, latrans
(= augusti of Zweifel) and E. tarahumarensis Taylor differ from
all other Eleutherodactylus (and Syrrhophus and Tomodactylus)
in the nature of the tips of the digits (external and skeletal). The
digits of Hylactophryne are like those of Eupsophus. My study of
nearly all genera of leptodactylids indicates that Noble (1925) was
correct in suggesting that Borborocoetes (= Eupsophus) is a close
relative of Eleutherodactylus latrans, although Noble's arguments
were based in part upon false evidence concerning the breeding
habits of E. latrans, then thought to have a free-living tadpole.

Kellogg (1932) and Piatt (1934) argued that the terminal phalanges
of E. latrans were typically eleutherodactyline. The variation
of this character in Eupsophus (see Fig. 4) ranges from
knobbed to bifurcate or Y-shaped (T-shaped in Eleutherodactylus,[Pg 514]
Syrrhophus and Tomodactylus) and encompasses the nature of the
character represented in Hylactophryne. Eupsophus differs from
Hylactophryne in possessing a frontoparietal fontanelle, in generally
having a maxillary-quadratojugal gap, and in having a free swimming
tadpole stage.

Fig. 5. Outline drawings of Leptodactylus melanonotus (left, KU 65704, × 2)
and Eleutherodactylus alfredi (right, KU 93994, × 2).

KEY TO MEXICAN LEPTODACTYLID GENERA

[Pg 515]

LITERATURE CITED

Dixon, J. R.

1957. Geographic variation and distribution of the genus Tomodactylus
in Mexico. Texas Jour. Sci., 9:379-409, December.

Duellman, W. E.

1958. A review of the frogs of the genus Syrrhophus in western Mexico.
Occas. Papers Mus. Zool. Univ. Michigan, 594:1-15, June 6.

1961. The amphibians and reptiles of Michoacan, Mexico. Univ. Kansas
Publ. Mus. Nat. Hist., 15:1-148, December 20.

Firschein, I. L.

1954. Definition of some little understood members of the leptodactylid
genus Syrrhophus, with a description of a new species. Copeia,
1:48-58, February 19.

Gallardo, J. M.

1965. A proposito de los Leptodactylidae (Amphibia Anura). Papeis
Avulsos, 17:77-87, January 30.

Gorham, S. W.

1963. The comparative number of species of amphibians in Canada and
other countries. III. Summary of species of anurans. Canadian
Field-Nat., 77:13-48, March.

Griffiths, I.

1959. The phylogeny of Sminthillus limbatus and the status of the
Brachycephalidae (Amphibia Salientia). Proc. Zool. Soc. London,
132:457-87, May.

Kellogg, R.

1932. Mexican tailless amphibians in the United States National Museum.
Bull. U. S. Natl. Mus., 160:224 pp., March 31.

Lloyd, J. J.

1963. Tectonic history of the south Central-American orogen, in Childs
and Beebe eds., Backbone of the Americas. Amer. Assoc. Petroleum
Geol., pp. 88-100.

Lynch, J. D.

1965. A review of the eleutherodactylid frog genus Microbatrachylus
(Leptodactylidae). Nat. Hist. Misc., 182:1-12, December 15.

Myers, G. S.

1962. The American leptodactylid frog genus Eleutherodactylus, Hylodes
(= Elosia), and Caudiverbera (= Calytocephalus). Copeia,
1:195-202, April 11.

Noble, G. K.

1925. An outline of the relation of the ontogeny to phylogeny within the
Amphibia. I. Amer. Mus. Nov., 165:1-17, April 16.

Piatt, J.

1934. The systematic status of Eleutherodactylus latrans (Cope). Amer.
Midl. Nat., 15:89-91, February 15.

Smith, H. M. and Taylor, E. H.

1948. An annotated checklist and key to the Amphibia of Mexico. Bull.
U. S. Natl. Mus., 194:1-118. June 7.

[Pg 516]

Taylor, E. H.

1952. A review of the frogs and toads of Costa Rica. Univ. Kansas Sci.
Bull., 35:577-942, July 1.

Zweifel, R. G.

1956. A survey of the frogs of the augusti group, genus Eleutherodactylus.
Amer. Mus. Novitates, 1813:1-35, December 23.

Transmitted July 11, 1967.

31-9418

Transcriber's Notes

Illustrations have been moved to avoid breaking up paragraphs of text.

Page 507: Changed know to known (are not know in Tomodactylus).

Page 507: Added closing parenthesis in Fig. 2 caption after × 3.

Page 509: Changed compeltely to completely (compeltely roofed skulls).

Page 512: Veracruuz may be a typo for Veracruz (Sinaloa to Veracruuz).

Page 514: Changed two occurrences of Hylatophryne to Hylactophryne.