Taken from: National Audubon
Society Field Guide
to North American Reptiles and Amphibians
Copyright: Chanticleer Press, Inc., 1979
Living amphibians comprise three major groups, 2 of which occur in
The salamanders (order Caudata) and the frogs and toads
(order Salientia). While
the oldest fossil salamanders and frogs can
only be traced back about 150 million
years, their ancestors evolved
from the fishes of the early Devonian Period,
appearing about 350
million years ago. The amphibians were the first vertebrates
the rigors of life on land. They solved locomotion and air breathing
problems but remained terrestrial existence and were never able to
completely from the aquatic environment. However,
skin and shelled eggs offered
protection against excessive water
loss, thus enabling them to advance into an
unoccupied arid habitat.
FROGS AND TOADS
There are nearly
2,700 species of frogs and toads known. They are divided into 16
families, with 9 occurring in North America. The remainder are found
in South America,
Europe, Africa, Asia, Australia, and the South
Pacific islands. A total of 81 species
occur north of Mexico.
Adult frogs and toads lack tails. They have well-developed
forelimbs and even larger
hind legs. They lack a clear neck, the
head seeming to be attached directly to the body.
Most have a
well-developed ear, as evidenced externally by a conspicuous tympanum,
voice used to attract mates, drive off intruders, and to signal
distress and presence.
All are carnivorous as adults. With their
moist skin, most frogs and toads are prone
to desiccation, and
therefore are confined to wet or moist habitats. However, some
species have adapted to more arid habitats by burrowing into the
soil or hiding
beneath rocks or logs to avoid the heat of the day.
Most species return to water to breed. Eggs laid in the
water are fertilized by the male
while clasping the female. The eggs
hatch into tadpoles which later transform into
young frogs. A number
of frogs and toads lay their eggs in shaded moist sites on land,
in nests constructed over water. The eggs may hatch into tadpoles
that either drop
into the water, are swept into the water by rains,
or are carried to water by the parent.
Other species bypass the
tadpole stage, their eggs hatching directly into miniature
Finally, the African live-bearing toad, Nectophrynoides, and the North
tailed frog, Ascaphus, are unique among frogs and toads in
fertilizing the eggs within
the cloaca of the female.
TAILED FROG FAMILY
Leiopelma with 3 species in New Zealand, and Ascaphus with 1 species
northwestern United States and southwestern Canada.
These are primitive frogs with 2 pairs of unattached ribs and 9
presacral vertebrae. The
pupil is vertical. None of the species has
a true tail, but all possess tail-wagging muscles.
have a unique tail-like extension of the vent that serves as a
organ for passing sperm directly into the body of the
female, while clasping her around
frogs live in cool mountain habitats, but reproduction varies:
lays its eggs on damp earth where they hatch 6 weeks
later as miniature frogs; Ascaphus lays
its eggs in cold mountain
streams where they hatch into tadpoles, transforming into frogs
than 6 months later.
Tailed Frog (Ascaphus
Only 1 species, Rhinophrynus dorsalis, found from Costa Rica to Texas.
This frog lacks a breastbone. The pupil is vertical. In addition, its tongue is attached in
the back and free in the front, unlike the typical toad or frog, so that it protrudes like the
tongue of most vertebraes. Rhinophrynus is adept at burrowing, making use of the spade on each
hindfoot to shuffle backward into the soil. Breeding males clasp the female around the waist.
Eggs are laid in water.
Mexican Burrowing Toad (Rhinophrynus
SPADEFOOT TOAD FAMILY
Ten genera with 69 species known; 1 genus in North America: Scaphiopus, with 5 species.
Spadefoots derive their names from the "spade," a horny, dar, sharp-edged tubercle on the inner
surface of the hind foot, used to dig their daytime burrow. Scaphiopus differs from other North
American coccyx, the bony end of the vertebral column, fused to the sacral vertebra.
The teeth on their upper jaw, the vertical pupils, relatively smooth skin, and absence of parotoid
glands easily separate them from true toads (Family Bufonidae).
Breeding males clasp the female around the waist. Scaphiopus breeds in temporary rainpools which
may dry up soon after the rains end. As an adaptation to this, spadefoots have an accelerated
development. The total period of time from egg to tadpole to metamorphosed toad can be as little
as 2 weeks.
Plains Spadefoot (Scaphiopus
Couch's Spadefoot (Scaphiopus couchi)
Western Spadefoot (Scaphiopus hammondi)
Eastern Spadefoot (Scaphiopus holbrooki)
Great Basin Spadefoot (Scaphiopus intermontanus)
TRUE FROG FAMILY
Forty-six genera with approximately 560 species worldwide. Only 1 genus in North America:
Rana, with 21 species.
True frogs have a bony breastbone and horizontal pupils. North American species are large
frogs with slim waists, long legs, pointed toes, and extensive webbing on the hind feet. They are
excellent jumpers. The adults are truly amphibious, typically living along the edge of water and
entering it daily to catch prey, flee danger, or to mate.
They are all voracious carnivores, feeding primarily on insects, spiders, and crustaceans, but
readily accepting anything else that can be caught and swallowed.
Mating usually is initiated in the spring with aggregations of males calling in chorus to
attract females to the breeding site. The breeding male has swollen forearms and thumbs for
clasping the female behind her forelegs. In the water, female Rana may lay strings or rafts
containing up to 20,000 eggs. Eggs hatch within a month, with tadpoles metamorphosing into
frogs 6 to 24 months later.
Crawfish Frog (Rana areolata)
Red-legged Frog (Rana aurora)
Rio Grande Leopard Frog (Rana berlandieri)
Plains Leopard Frog (Rana blairi)
Foothill Yellow-legged Frog (Rana boylei)
Cascades Frog (Rana cascadae)
Bullfrog (Rana catesbeiana)
Green Frog (Rana clamitans)
Las Vegas Leopard Frog (Rana fisheri)
Pig Frog (Rana grylio)
River Frog (Rana heckscheri)
Mountain Yellow-legged Frog (Rana muscosa)
Relict Leopard Frog (Rana onca)
Pickeral Frog (Rana palustris)
Northern Leopard Frog (Rana Pipiens)
Spotted Frog (Rana Pretiosa)
Mink Frog (Rana septentrionalis)
Southern Leopard Frog (Rana sphenocephala)
Wood Frog (Rana sylvatica)
Tarahumara Frog (Rana tarachumarae)
Carpenter Frog (Rana virgatipes)
NARROW-MOUTHED FROG FAMILY
Sixty-one genera with approximately 270 species known. Only 2
genera occur in our range:
Gastrophryne with 2 species, and Hypopachus with 1 species.
Narrow-mouthed frogs have a reduced shoulder girdle. The North American species lack teeth,
and have a fold of skin across the back of the narrow, pointed head. The body is plump and
the skin smooth and moist. The legs are short and the hind feet have enlarged tubercles
used in digging. They are secretive creatures active only at night; they feed almost
exclusively on ants.
Males give a bleating call to attract females to the breeding ponds. In addition to being
clasped firmly behind the forlimbs by the male, the female narrow-mouthed's sticky skin
secretion also holds the breeding pair together. Eggs are laid in a thin floating film and
hatch in a few days. Tadpoles metamorphose in about 30 days.
Eastern Narrow-mouthed Frog (Gastrophryne carolinensis)
Great Plains Narrow-mouthed Frog (Gastrophryne olivacea)
Sheep Frog (Hypopachus variolosus)
Nineteen genera with approximately 300 species known. Only 1 genus occurs in our range:
Bufo, with 18 species.
Toads are squat and plump with rough warty skin. They have horizontal pupils, no teeth
on the upper jaw, and lack an anterior breastbone. Enlarged parotoid glands are located
on each side of the neck over or behind the tympanum. These glands secrete a viscous white
poison, which gets smeared in the mouth of any would-be predator. The poison inflames the
mouth and throat, causes nausea, irregular heart beat, and, in extreme cases, death.
Survivors of such a poisoning seldom ever again attack toads.
Bufo breeds in spring and summer. Males congregate at the breeding ponds and sing in
order to attract females. Males clasp the willing females around the body behind the
forelimbs. Males also have a rudimentary ovary, which can become functional if the
testes are damaged or removed. Eggs are usually laid in strings attached to vegetation;
they hatch into timy black tadpoles, which weeks later metamorphose.
Colorado River Toad (Bufo alvarius)
American Toad (Bufo americanus)
Western Toad (Bufo boreas)
Yosemite toad (Bufo Canorus)
Great Plains Toad (Bufo cognatus)
Green Toad (Bufo debilis)
Black Toad (Bufo exsul)
Canadian Toad (Bufo hemiophrys)
Houston Toad (Bufo houstonensis)
Giant Toad (Bufo marinus)
Southwestern Toad (Bufo microscaphus)
Red-spotted Toad (Bufo punctatus)
Oak Toad (Bufo quercicus)
Sonoran Green Toad (Bufo retiformis)
Texas Toad (Bufo Speciosus)
Southern Toad (Bufo terrestris)
Gulf Coast Toad (Bufo valliceps)
Woodhouse's Toad (Bufo woodhousei)
TREE FROG FAMILY
Thirty-four genera with approximately 600 species known. Seven genera with 26 species occur
in our range. Tree frogs are small and have slender legs; their pupils are horizontal.
Arboreal tree frogs are typically walkers and climbers-----they are reluctant jumpers. Their
toe tips are expanded into sticky adhesive pads used in climbing. Climbing is further aided
by the presence of a cartilage between the last 2 bones of each toe. The cartilage allows
the tip of the toe to swivel backward and sideways while keeping the sticky toe pad flat
against the climbing surface. A few tree frogs, such as the North American Acris, have
returned to a terrestrial existence, lack large toe pads, and are active leapers.
Male tree frogs in our range typically call while perched on vegetation in, over, or near water.
Males clasp females just behind the forelimbs; masses of eggs are laid in the water.
Northern Circket Frog (Acris crepitans)
Southern Cricket Frog (Acris gryllus)
Pine Barrens Tree frog (Hyla andersoni)
Canyon Tree frog (Hyla arenicolor)
Bird-voiced Tree frog (Hyla avivoca)
California Tree frog (Hyla cadaverina)
Cope's Gray Tree frog (Hyla chrysoscelis)
Common Gray Tree frog (Hyla versicolor)
Green Tree frog (Hyla cinerea)
Spring Peeper (Hyla crucifer)
Mountain Tree frog (Hyla eximia)
Pine Woods Tree frog (Hyla femoralis)
Barking Tree frog (Hyla gratiosa)
Pacific Tree frog (Hyla regilla)
Squirrel Tree frog (Hyla squirella)
Little Grass Frog (Limnaoedus ocularis)
Cuban Tree frog (Osteopilus septentrionalis)
Mountain Chorus Frog (Pseudacris brachyphona)
Brimley's Chorus Frog (Pseudacris brimleyi)
Spotted Chorus Frog (Pseudacris clarki)
Southern Chorus Frog (Pseudacris nigrita)
Ornate Chorus Frog (Pseudacris ornata)
Strecker's Chorus Frog (Pseudacris streckeri)
Chorus Frog (Pseudacris triseriata)
Burrowing Tree frog (Pternohyla fodiens)
Mexican Tree frog (Smilisca baudini)
LEPTODACTYLID FROG FAMILY
Fifty genera of about 650 species occur in Australia, southern Africa, and the tropical
Americas; 4 genera with 7 species occur in our range.
Leptodactylids are an extremely diverse group adapted to a variety of habitats and
reproductive strategies. The 7 species that occur in our section of North America
have horizontal pupils and a T-shaped bone in the tip of each toe.
Males of some species congregate together to call in loud choruses to attract females
to the breeding ponds, but males of most species call singly, often while hidden in
vegetation or burrows. Breeding males clasp the females behind the forelimbs. Some
species, like Leptodactylus, lay numerous eggs in foam nests in the water. On hatching,
the tadpoles escape inot the water where they live until metamorphosing into frogs.
Other species, like Eleutherodactylus, lay fewer than two dozen eggs in moist leaf
litter or damp earth. They hatch 2 to 3 weeks later, releasing fully developed
Puerto Rican Coqui (Eleutherodactylus coqui)
Greenhouse Frog (Eleutherodactylus planirostris)
Barking Frog (Hylactophryne augusti)
White-lipped Frog (Leptodactylus labialis)
Rio Grand Chirping Frog (Syrrhophus cystignathoides)
Spotted Chirping Frog (Syrrhophus guttilatus)
Cliff Chirping Frog (Syrrhophus marnocki)
TONGUELESS FROG FAMILY
Four genera: Pipa with 6 species in South America, and Xenopus, Hymenochirus, and
Pseudhymenochirus with 14 species in Africa. One species Xenopus laevis, has been
introduced to North America.
Tongueless frogs have attached ribs and eight presacral vertebrae. Their pupils are
round. The South American species have starlike projections on the tips of the toes
of the front feet; the African species have simple pointed toes on the front feet.
The latter attach their eggs singly to submerged vegetation, logs, or stones;
thousands of eggs are laid. During breeding, males clasp the female around the waist.
African Clawed Frog