southern Mexico and northern Central America gives some idea of
relative lengths of time of isolation from related populations. Those
populations inhabiting high mountain environments on either side of the
isthmus are specifically distinct. Some populations inhabiting cloud
forests lower on the mountains are specifically distinct from related
populations on the other side of the isthmus; between others there is
no recognizable differentiation. Even though many populations are
isolated from other populations of the same species in the lowlands of
the isthmus, there is no apparent speciation. This indicates that the
lowland environments and their inhabitants have been isolated from one
another for a shorter time than have the highland environments and
their inhabitants.
ACCOUNTS OF SPECIES
For each species of amphibian known to occur in the lowlands of the
Isthmus of Tehuantepec, localities where one or more specimens were
collected are listed, and variation, ecology, and life histories are
discussed. A total of 2833 specimens has been examined for the purposes
of this study. Individual specimens cited in the text are listed with
catalogue numbers and abbreviations of the name of the museum, as
follows:
AMNH American Museum of Natural History
KU University of Kansas Museum of Natural History
MCZ Museum of Comparative Zoology, Harvard College
UIMNH University of Illinois Museum of Natural History
UMMZ University of Michigan Museum of Zoology
USNM United States National Museum
=Gymnopis mexicanus mexicanus= Dumeril and Bibron
_Oaxaca_: El Barrio (3); Matias Romero; Tehuantepec (2).
_Veracruz_: Cosamaloapan; Cuatotolapam (2).
The two specimens from Cuatotolapam were collected by Ruthven in an
area of mixed savanna and forest. The three specimens (USNM 30535-7)
listed above from El Barrio were collected by Sumichrast; possibly they
came from another locality. The city of Tehuantepec is divided into
seven districts called "barrios." The two specimens listed from
Tehuantepec (MCZ 1604) merely bear the data "Tehuantepec, Mexico." They
may have come from the town, the district, or from anywhere in the
isthmus. The specimen from Matias Romero has 109 primary and 67
secondary annuli, a length of 400 mm., and a diameter of 19 mm.; the
one from Cosamaloapan has 106 primary and 58 secondary annuli, a length
of 397 mm., and a diameter of 19 mm. Data on the other specimens were
recorded by Dunn (1942:475).
=Bolitoglossa occidentalis= Taylor
_Oaxaca_: Rio Sarabia (2); Ubero. _Veracruz_: La Oaxaquena;
14 km. E of Suchil.
The specimens from Oaxaca are only tentatively assigned to
_occidentalis_. All are immature and lack maxillary teeth. Taylor
(1941:147) stated that the maxillary teeth are absent in young
_occidentalis_. One from Rio Sarabia is a male with a body-length of 29
mm. and a tail-length of 22 mm. The dorsum is reddish brown streaked
with dark gray; the venter is dark gray. Two small individuals (one
from Sarabia and one from Ubero) have body-lengths of 19 and 21 mm. and
tail-lengths of 10.5 and 11 mm. In life they were pale yellowish tan
above with a brown triangular mark on the occiput, but with no
middorsal stripe. Both were found in the axils of elephant ear plants
(_Xanthosoma_).
This species has been noted by Goodnight and Goodnight (1956:146) on
the Atlantic lowlands at Palenque, Chiapas, and by Shannon and Werler
(1955:362) at several localities in Los Tuxtlas, Veracruz. I have
collected it at Vista Hermosa on the eastern slopes of the Sierra Madre
Oriental above Tuxtepec in northern Oaxaca. Both _B. occidentalis_ and
_B. rufescens_ have been reported from Palenque, Chiapas (Taylor and
Smith, 1945:547). Reexamination of specimens from northern Chiapas and
Tabasco is needed to verify the sympatric occurrence of these two
similar species.
=Bolitoglossa platydactyla= Tschudi
_Oaxaca_: La Oaxaquena; Tolosita (2). _Veracruz_: Acayucan;
Cuatotolapam; 25 km. ESE of Jesus Carranza; 14 km. E of
Suchil; 2.7 km. N of Tula.
Known only from the Gulf lowlands in the isthmian region, this species
has been taken in a variety of habitats within the humid forest area:
under outer leaves of banana plants, under a rock along a stream, under
a log in a plowed field, and on a reed in a pond at night. Three adult
males have an average snout-vent length of 44 mm. and a tail-length of
41 mm. In life the color of the dorsum varied from orange-yellow to
orange-tan, usually being more orange on the tail. The iris was a
reddish orange.
=Bolitoglossa veracrucis= Taylor
_Veracruz_: 35 km. SE of Jesus Carranza (21).
This species is known only from the type series collected at night on a
limestone cliff by Walter W. Dalquest. If this salamander is restricted
to this type of habitat, it should be found in the region of extensive
limestone outcroppings in northern Chiapas and southern Tabasco.
=Rhinophrynus dorsalis= Dumeril and Bibron
_Oaxaca_: Ixtepec; Limon; Salina Cruz (18); Tehuantepec
(57); Tuxtepec (3). _Veracruz_: Amatitlan (3); Cosamaloapan
(5); Novillero (2); San Lorenzo.
This species inhabits the scrub forests of the Pacific coastal plain
and the savannas in southern Veracruz; apparently it does not occur in
rainforest. Consequently, its distribution in the isthmus is
discontinuous.
PLATE 1
[Illustration: FIG. 1. Savanna about 75 kilometers east of
Coatzacoalcos, Veracruz. Photograph by L. C. Stuart.]
[Illustration: FIG. 2. Low scrub forest near Alvarado, Veracruz.
Photograph by L. C. Stuart.]
PLATE 2
[Illustration: FIG. 1. Rainforest near Tolosita, Oaxaca. March, 1956.]
[Illustration: FIG. 2. Rainforest along the Rio Sarabia, Oaxaca. March,
1956.]
PLATE 3
[Illustration: FIG. 1. Transition forest near La Princesa, Oaxaca.
March, 1956.]
[Illustration: FIG. 2. Palm Savanna on the Plains of Chivela, Oaxaca.
March, 1956.]
PLATE 4
[Illustration: FIG. 1. Scrub forest on the Plains of Tehuantepec in dry
season. March, 1956.]
[Illustration: FIG. 2. Scrub forest on the Plains of Tehuantepec in
rainy season. View toward the north. In the distance is the Continental
Divide in the hills of the Isthmus. July, 1958.]
PLATE 5
[Illustration: FIG. 1. Low, dense scrub forest near La Ventosa, Oaxaca.
July, 1958.]
[Illustration: FIG. 2. Temporary pond in scrub forest north of Salina
Cruz, Oaxaca. July 7, 1958. _Rhinophrynus dorsalis_, _Bufo marmoreus_,
and _Diaglena reticulata_ were breeding here the previous night.]
PLATE 6
[Illustration: FIG. 1. Calling male of _Rhinophrynus dorsalis_,
photographed in a pond north of Santa Cruz, Oaxaca, on July 6, 1958.
x 2/3.]
[Illustration: FIG. 2. Color pattern variation in two adults of _Bufo
canaliferus_ from Juchitan, Oaxaca. x 2/3.]
PLATE 7
[Illustration: FIG. 1. Calling male of _Engystomops pustulosus_,
photographed in a pond west of Tehuantepec, Oaxaca, on July 5, 1956.
x 2.]
[Illustration: FIG. 2. Foamy egg mass of _Engystomops pustulosus_ at
the edge of a pond west of Tehuantepec, Oaxaca. July 5, 1956. x 3/8.]
PLATE 8
[Illustration: FIG. 1. Calling male of _Diaglena reticulata_,
photographed at a pond north of Salina Cruz, Oaxaca, on July 6, 1958.
x 1/2.]
[Illustration: FIG. 2. Clasping pair of _Diaglena reticulata_ at the
edge of a pond north of Salina Cruz, Oaxaca, on July 6, 1958. x 1.]
Breeding congregations were found after heavy rains at Tehuantepec on
July 5, 1956, at Cosamaloapan, Novillero, and Amatitlan on July 26,
1956, and at Salina Cruz on July 6, 1958. The call is a long "worrp"
made while the male is floating on the surface of the pond. The small
heads, small limbs, and greatly inflated bodies cause the calling males
to resemble miniature caricature balloons (Pl. 6, fig. 1). Amplexus is
inguinal. These toads are notably wary, even when calling. Often the
beam of a flashlight or the slightest disturbance of the water will
cause the males to stop calling. The body is deflated with one last
nauseous note, and the frog sinks beneath the surface of the water and
swims away with short slow kicks of the hind feet.
=Bufo canaliferus= Cope
_Oaxaca_: Chivela; Salina Cruz; Santa Efigenia; Tapanatepec
(6); Tehuantepec (10); Zanatepec (4).
This small toad apparently is restricted to the Pacific lowlands from
the Isthmus of Tehuantepec eastward to Guatemala. At Zanatepec on July
13, 1956, males were calling from a flooded field bordered by scrub
forest. The call is a rather loud nasal racket. Living individuals vary
greatly in coloration. Some have yellowish tan flanks and dorsum and an
orange middorsal stripe; others have a pale red dorsum, yellow flanks,
and a cream middorsal stripe (Pl. 6, fig. 2).
=Bufo coccifer= Cope
_Oaxaca_: Juchitan (5); Tehuantepec.
It is with some degree of hesitancy that these toads are referred to
the species _coccifer_. Although these and other specimens from
Guerrero and Michoacan display no striking differences from specimens
from Costa Rica, Nicaragua, and southeastern Guatemala, the ranges of
the populations are separated by a broad hiatus in Chiapas and
Guatemala. Possibly this species has utilized the sub-humid corridor
through northern Central America (Stuart, 1954) and subsequently
disappeared from the corridor in Guatemala and Chiapas. Specimens of a
_coccifer_-like toad collected by Stuart in the vicinity of
Jacaltenango, Departamento Huehuetenango, Guatemala, are much larger
than either the Central American or Mexican specimens of _coccifer_. A
final commitment on the systematic status must await a thorough study
of this group of toads.
Males of this species were calling from a grassy rain-pool in open
scrub forest at the edge of Juchitan on July 6, 1956. The call is a
low "whirrr." The calling males were sitting in the shallow water at
the edge of pond, where they were hidden by the grass. None was
observed in open water, as is characteristic of calling males of _Bufo
canaliferus_ and _marmoreus_.
=Bufo marinus= Linnaeus
_Oaxaca_: Agua Caliente; Guichicovi (3); Mixtequilla;
Tolosita (6); Tehuantepec (37); Tuxtepec; Union Hidalgo.
_Veracruz_: Ciudad Aleman (4); Cosamaloapan; Cuatotolapam
(19); 20 km. SE of Jesus Carranza (4); 38 km. SE of Jesus
Carranza (10); 20 km. NE of Jesus Carranza (4); Novillero.
This large toad is abundant throughout the lowlands of the isthmus. The
loud rattling call of males was heard on rainy nights throughout the
summer. In March, 1956, several adults were found in a small cave back
of a spring at Agua Caliente.
=Bufo marmoreus= Wiegmann
_Oaxaca_: Cerro San Pedro (2); Chivela (5); Escurano (3);
Juchitan; Salina Cruz (101); Santa Lucia (2); 12 km. S of
Santiago Chivela (11); Santo Domingo; Tapanatepec;
Tehuantepec (100); Tequisistlan. _Veracruz_: Alvarado;
Coatzacoalcos.
This toad is abundant on the Pacific lowlands, where it inhabits both
open and dense scrub forest. On the Gulf lowlands its distribution
seems to be limited to xeric coastal habitats. Aside from the specimens
from Alvarado and Coatzacoalcos, it is known in Veracruz only from Boca
del Rio (Langebartel and Smith, 1959:27).
The similarity in size of _Bufo marmoreus_ and _valliceps_ and their
almost completely allopatric ranges suggest that the two species may be
in competition at any one locality. Nevertheless, both were calling
from a small rocky stream south of Santiago Chivela on July 6, 1956.
On the night of July 6, 1958, an estimated 400 toads of this species
made up a breeding congregation near Salina Cruz. The site was a
shallow muddy pond about 20 x 40 meters located in an area cleared of
scrub forest; the banks of the pond were devoid of vegetation (Pl. 5,
fig. 2). Breeding in the same pond were _Rhinophrynus dorsalis_ and
_Diaglena reticulata_. The following morning no more than a dozen
_Bufo_ were found in the pond, but several individuals were found
beneath debris and in small burrows near the pond. On July 7, 1958,
large numbers of tadpoles and recently metamorphosed young were in a
shallow grassy pool just east of Salina Cruz.
Taylor (1943b:347) referred certain specimens from Tehuantepec to _Bufo
perplexus_, a species closely related to _Bufo marmoreus_. Evidence to
be presented elsewhere shows that _perplexus_ does not occur in the
isthmus.
=Bufo valliceps valliceps= Wiegmann
_Oaxaca_: Guichicovi (2); Matias Romero; 32 km. N of Matias
Romero (2); Nueva Raza; Rio Sarabia (3); Santa Maria
Chimalapa (14); Santiago Chivela; 12 km. S of Santiago
Chivela (5); Santo Domingo (5); Tolosita (7). _Veracruz_:
Acayucan (3); Alvarado; Amatitlan; Ayentes; Cosamaloapan
(3); Cosoleacaque (6); Cuatotolapam (14); Hueyapan; 20 km.
ENE of Jesus Carranza (6); 20 km. S of Jesus Carranza; 25
km. SE of Jesus Carranza (23); 35 km. SE of Jesus Carranza;
60 km. SW of Jesus Carranza (5); La Oaxaquena (4); Novillero
(4); San Lorenzo (5).
Individuals were found in both wet and dry seasons. In the dry season
they were most frequently found in rainforest, whereas in the rainy
season breeding congregations were found in savannas as well. This toad
occurs throughout the Gulf lowlands and on the Pacific slopes and in
the Grijalva Valley of Chiapas and Guatemala, but not on the Pacific
lowlands of the isthmus.
I have not been able to recognize individuals referrable to the race
_macrocristatus_. Firschein and Smith (1957:219) described
_macrocristatus_ from the mountains of eastern Oaxaca and referred to
it specimens from the Gulf lowlands of northern Chiapas. None of the
present material shows the hypertrophied cranial crests supposedly
characteristic of _macroaristatus_, nor do specimens from the isthmus
resemble the population in the Grijalva Valley being described by L. C.
Stuart, who will discuss the variation in, and the validity of, the
named populations of _valliceps_.
Five specimens from San Lorenzo, Veracruz (USNM 123516-20), were
identified as _Bufo cristatus_ by Smith (1947:408). Firschein (1950:83)
redefined the _cristatus_ group of _Bufo_ and assigned these specimens
to _valliceps_.
=Eleutherodactylus alfredi= Boulenger
_Oaxaca_: Tolosita (2). _Veracruz_: 35 km. SE of Jesus
Carranza (6).
These specimens were collected in rainforest. Shreve (1957:247) pointed
out the close resemblance between _E. alfredi_ and _E. conspicuus_ from
Piedras Negras, Guatemala, and treated them as subspecies. Examination
of the specimens from the isthmus, together with seven from central
Veracruz and one from Teapa, Tabasco, suggests an even closer
relationship. _Eleutherodactylus conspicuus_ was diagnosed by Taylor
and Smith (1945:567) as differing from _alfredi_ "in lacking a tarsal
fold, in having shorter hind legs with the tibiotarsal articulation
reaching only to the nostril instead of beyond the tip of the snout;
the vomerine teeth barely reach the posterior level of the choanae."
The specimen from Teapa has the vomerine teeth reaching to the
posterior edge of the choanae; in the eight specimens from the isthmus
the teeth reach the posterior edge of the choanae in two and to the
middle of the choanae in six; in seven specimens from central Veracruz
the teeth reach the posterior edge of the choanae in two and to the
middle in five. The tibiotarsal articulation extends beyond the tip of
the snout in the specimen from Teapa and in two from central Veracruz;
in three specimens from the isthmus and in one from central Veracruz it
extends only to the nostril; in the others it extends to the snout. The
tarsal fold is absent in the specimen from Teapa, in three from the
isthmus, and in all those from central Veracruz; it is weakly present
in the others.
In the light of this evidence there seems to be little justification in
recognizing two species or even two subspecies in this group.
Consequently, _Eleutherodactylus conspicuus_ Taylor and Smith (1945) is
here placed in the synonymy of _Eleutherodactylus alfredi_ Boulenger
(1898), a species with a range extending from Cuautlapan and Potrero
Viejo in central Veracruz southward and eastward in forested habitats
to western El Peten, Guatemala.
=Eleutherodactylus natator= Taylor
_Veracruz_: 35 km. SE of Jesus Carranza (3); 38 km. S of
Jesus Carranza; 55 km. SE of Jesus Carranza.
The snout-vent length is 42.0 mm. in a male and averages 59.5 mm. in
three adult females. The tarsal fold is low and extends about half the
length of the tarsus; the first and second fingers are subequal in
length; the tibiotarsal articulation extends beyond the tip of the
snout. The patches of vomerine teeth lie between the posterior margins
of the choanae. The throat and belly are immaculate, and the soles of
the feet are dark. In the isthmus this species can be distinguished
from _Eleutherodactylus rugulosus_ by less rugose skin on the dorsum
and absence of dark ventral mottling.
The specimens reported here extend the known range of _natator_
eastward from Camotlan, Oaxaca; northward in Veracruz the species
inhabits foothills as far north as Huatusco.
=Eleutherodactylus rhodopis= Cope
_Oaxaca_: 30 km. N of Matias Romero; Rio Sarabia (5);
Tapanatepec (87); Tolosita (6); between Zanatepec and
Tapanatepec. _Veracruz_: 25 km. SE of Jesus Carranza; 35 km.
SE of Jesus Carranza (2); 22 km. SSW of Jesus Carranza; 20
km. ENE of Jesus Carranza (7); Minatitlan; Tapalapan (5).
For the purposes of the present study I am not recognizing
_Eleutherodactylus beati_, _E. dorsoconcolor_, and _E. venustus_ as
specifically, or even subspecifically distinct from the earlier named
_E. rhodopis_. Probably these are mere color varieties of a single
species.
In the dry season frogs of this species were in humid forests, where
they were most frequently found along small streams and in ravines. The
species is widespread in the Gulf lowlands, but does not occur on the
Plains of Tehuantepec. It does inhabit the Pacific slopes on the
foothills of the Sierra Madre de Chiapas, the western part of which
extends into eastern Oaxaca near Tapanatepec.
=Eleutherodactylus rugulosus= Cope
_Oaxaca_: La Princesa (30); Modelo; Santa Lucia (10);
Tapanatepec (26); Tehuantepec (6); Tres Cruces (8).
_Veracruz_: Tapalapan (5).
In addition to the specimens from the lowlands of the isthmus, for the
purposes of the following discussion, I have included data on two
specimens from the southern slopes of the Sierra del Sur in Oaxaca
(Mirador and Chacalapa) and on several specimens from Los Tuxtlas in
Veracruz (Los Chaneques, 67; Salto de Eyipantla, 35; and San Andres
Tuxtla, 11).
Frogs of the _Eleutherodactylus rugulosus_ complex occur from southern
Veracruz and Sinaloa southward through Central America. Taylor
(1940:401) described _E. vocalis_ from Hacienda El Sabino, Michoacan;
Taylor and Smith (1945:580) described _E. avocalis_ from Tres Cruces,
Oaxaca. These have been considered as species distinct from
_rugulosus_, which is known to occur in Veracruz, Guerrero, and Chiapas
southward into Central America. Although the large number of specimens
collected in the isthmus does not aid in defining the ranges of the
taxa involved, these specimens do give some idea of the variation in
certain characters in a given population.
In specimens from Los Tuxtlas the tarsal fold is well-developed and
extends two-thirds to three-fourths the length of the tarsus; the
tibiotarsal articulation reaches the nostril and sometimes slightly
beyond the tip of the snout. In males the tympanum is nearly equal to
the diameter of the eye; in females it is about one-half the diameter
of the eye. The posterior surfaces of the thighs are dark brown or
black with whitish or cream-colored spots, flecks, or irregular
mottling. The tarsal fold is dark; the throat is pale in some
individuals, but in most is mottled with dark brown or gray flecks.
Individuals from La Princesa near the continental divide in Oaxaca show
the same variation in body proportions and development of the tarsal
fold. The posterior surfaces of the thighs are dark brown indistinctly
mottled with lighter brown. The throat is dark brown. Specimens from
the Pacific slopes of Oaxaca, including the Plains of Tehuantepec, have
dark brown thighs mottled with dusty cream. The tibiotarsal
articulation extends slightly beyond the tip of the snout in all
specimens. In males the tympanum is equal to about two-thirds the
diameter of the eye. Duellman (1958b:6) discussed the variation in
these characters in populations in Colima, Jalisco, and Michoacan.
Until the extent of variation of these characters is known throughout
the range of _rugulosus_, the recognition of populations either as
species or subspecies seems superfluous. Consequently, I have used the
oldest name; this does not necessarily imply, however, that all
populations of _rugulosus_ (_sensu lato_) are conspecific.
Of the 200 specimens examined, 15 have a middorsal stripe that is red
or yellow. The iris varies from a copper to a dark golden color and
shines bright red at night. Many of the specimens are juveniles; these
were collected in the dry season, at which time they were found beneath
rocks along streams, in road culverts where there was some water, and
in holes in banks and cliffs.
=Microbatrachylus pygmaeus= Taylor
_Oaxaca_: La Princesa (5); Matias Romero (9); Rio Sarabia
(41); Tolosita (2). _Veracruz_: Jesus Carranza; 20 km. ENE
of Jesus Carranza.
The specimens listed above vary widely in color patterns; some of the
patterns are characteristic of certain named "species": _albolabris_,
_imitator_, _lineatissimus_, and _minimus_. The large series from the
Rio Sarabia contains all of the color patterns; this series was
obtained in one small ravine in the rainforest. At least in the
isthmian region, this species does not inhabit the Pacific slopes and
lowlands.
=Syrrhophus leprus= Cope
_Oaxaca_: 33 km. N of Matias Romero; Santa Efigenia.
_Veracruz_: San Lorenzo.
Although the type locality is stated to be Santa Efigenia on the
Pacific slopes of the Sierra Madre de Chiapas in eastern Oaxaca, the
type specimen probably came from the northern slopes of the mountains.
All other known specimens are from the Gulf slopes and lowlands, and
from several localities in Los Tuxtlas. Details concerning specimens
from the isthmus and other parts of the range were given by Duellman
(1958c:8).
Smith (1947:408) reported a specimen of _Syrrhophus verruculatus_
Peters from San Lorenzo, Veracruz; he stated that this specimen (USNM
123530) could not be _S. leprus_, because it had a gray belly, nor _S.
cystignathoides_, because of the dark and light dorsal coloration.
Firschein (1954:57) in his review of the species of _Syrrhophus_ in
eastern Mexico referred the specimen to _S. cystignathoides_. The
specimen is in poor condition. Nevertheless, specific determination is
possible. Numerous specimens of _S. leprus_ from Los Tuxtlas have gray
bellies; some have heavier pigmentation than the specimen from San
Lorenzo. In preservative the dorsum is dark brown with lighter
mottling. There is little doubt that the specimen from San Lorenzo is
a _Syrrhophus leprus_, an abundant and widespread species in the
humid Gulf lowlands of southern Mexico, and not _verruculatus_, if
this is a valid species (see Firschein, _op. cit._:58), and not
_cystignathoides_, a species known from San Luis Potosi southward to
central Veracruz.
=Syrrhophus pipilans pipilans= Taylor
_Oaxaca_: Cerro Arenal; Cerro San Pedro; 6 km. N of Chivela;
14 km. W of Tehuantepec (2).
In the isthmian region this frog is known only from the Pacific slopes
and the Plains of Tehuantepec. Males call from the ground and from
trees to heights of about four meters. The call is a single, high, long
"peep."
=Engystomops pustulosus= Cope
_Oaxaca_: Chivela; La Ventosa (3); Santo Domingo;
Tapanatepec (14); Tehuantepec (61); Union Hidalgo (62).
_Veracruz_: Acayucan; Cuatotolapam (7); 10 km. SE of
Hueyapan (11).