Tailed frogs

(Ascaphidae)

Class Amphibia

Order Anura

Family Ascaphidae

Thumbnail description
Small, stream-dwelling frogs with broad heads, vertical pupils, no visible eardrum, long hind legs, rugose skin, and webbed hind feet with a thickened outermost toe; males have a tail-like extension of cloaca; tadpoles are dark and streamlined and have enlarged, ventral, suctorial lips bearing many rows of small denticles

Size
1.2–2.0 in (30 to 50 mm)

Number of genera, species
1 genus; 2 species

Habitat
Streams on forested mountains

Conservation status
Not threatened

Distribution
Northwestern North America

Evolution and systematics

Tailed frogs are considered to be among the most primitive of living frogs, rivaled in that position only by the leiopelmatid frogs of New Zealand. Their skeletal anatomy is remarkably similar to that of the earliest known fossil frogs from the Jurassic. The two species were distinguished from each other in 2001 based on genetic data, though at one time they were described as different subspecies. There is no fossil record. No subfamilies are recognized.

Physical characteristics

These are small brown or gray frogs with a pale patch on the snout. The head is broad, the nostrils are placed far apart, and the eyes have vertical, diamond-shaped pupils. A slight fold of skin curves back from the eye to the corner of the mouth. No tympanum is visible, and the dorsal skin is roughened with small tubercles. The toes of the hind feet are short, but the feet are webbed; the outermost toe of the hind foot is thicker than the rest of the toes. Adult males have a fleshy "tail," which is actually an extension of the cloaca and not a tail in the usual sense. Females are slightly larger than males. These frogs have small lungs and rely upon their vascularized skin for much of their respiratory gas exchange. Such reduced lungs do not present a problem to frogs living in fast-flowing, well-oxygenated streams. There are nine prescacral vertebrae, and small, free ribs are associated with the third, fourth, and fifth vertebrae. All other living frogs, except the New Zealand native frogs, genus Leiopelma, have eight or fewer presacral vertebrae and ribs that are fused to the vertebrae. The tadpoles are dark gray with wide heads dominated by a large, ventral sucker surrounding the mouth.

Distribution

Tailed frogs are found in the Pacific coastal mountainous region of North America from northern California north to the Nass River in British Columbia, but not on Vancouver Island (Ascaphus truei), and in the Rocky Mountains of Idaho, Montana, northeastern Oregon, southwestern Washington, and extreme southeastern British Columbia (Ascaphus montanus).

Habitat

Tailed frogs inhabit small, clear, unsilted, permanent mountain streams surrounded by forest; they tend to avoid steep gradients and flat, still waters.

Behavior

Tailed frogs hide under rocks during the day and emerge at night, especially during rains, to forage for food. The tadpoles tend to cling to rocks in fast-flowing currents or inhabit pools and riffles in the stream.

Feeding ecology and diet

Tailed frogs eat terrestrial and aquatic insects or other invertebrates. The tadpoles scrape algae and diatoms from rocks.

Reproductive biology

In the fall breeding season males develop black pads on the hands and black tubercles on their arms and sides. They do not vocalize. During mating amplexus is inguinal, and the "tail" is used for internal fertilization. The female lays 35–100 unpigmented eggs in small clusters under rocks in streams. The tadpoles take up to seven years to metamorphose and another three to eight years to reach maturity.

Conservation status

Not threatened.

Significance to humans

These frogs are of scientific interest, because they are among the most primitive of living frogs. They are also indicators of environmental health, in that they inhabit small, clear, unsilted streams devoid of fish.

Species accounts

List of Species

Rocky Mountain tailed frog

Ascaphus montanus

taxonomy

Ascaphus truei montanus Mittleman and Myers, 1949, tributary of Lincoln Creek, Glacier National Park, Flathead County, Montana, United States. Recognized as a species in 2001.

other common names

None known.

physical characteristics

The body is brown or gray with distinct, dense, fine black speckling on the dorsal and ventral surfaces. There is a light patch between the eyes that extends forward across the snout, but there are no spots or blotches on the back. The belly is pink. The toes of the hind feet are short, but the webbing of the hind foot is even more extensive than it is in the coastal tailed frog. Adults are 1.2–2.0 in (30–50 mm) long; females are slightly larger than males. The tadpoles are slate gray and up to 1.2 in (30 mm) long, with large, suctorial mouthparts. Within the mouth disc are broad, horny upper jaws and large numbers of labial teeth.

distribution

The species occurs in western North America in the Rocky Mountains and Columbia Mountains of Idaho, western Montana, northeastern Oregon, and southeastern Washington to extreme southeastern British Columbia.

habitat

This frog inhabits small, permanent, mid-elevation mountain streams.

behavior

During the day Rocky Mountain tailed frogs hide under rocks beside the stream or in nearby rivulets. At night they forage in the surrounding forest. Tadpoles are found in the swiftest-flowing parts of streams, and metamorphosing tadpoles tend to occur in pools where there are large boulders. The frogs face predatory threats from snakes, fish, larger frogs, birds, predatory invertebrates, and small mammals.

feeding ecology and diet

Rocky Mountain tailed frogs eat terrestrial and aquatic insects and forage under water as well as on land. To feed, tadpoles scrape algae off rocks with their rows of small teeth.

reproductive biology

Breeding occurs in the fall. In mid-summer females adhere 45–75 unpigmented eggs in small clusters to the undersides of rocks in streams. The tadpoles stay in pools until the suction-cup-like mouth develops fully. The tadpoles may take up to five years to metamorphose, and they do so usually in early spring to late summer. The newly transformed frogs typically do not reach sexual maturity for seven to eight years. These are long-lived frogs, estimated to live anywhere from 15 to 20 years.

conservation status

Not threatened.

significance to humans

These frogs are interesting because of their primitive morphologic features and unusual life history; they are of some importance because of their reliance on undamaged forested streams that are generally too small to maintain fish.

Coastal tailed frog

Ascaphus truei

taxonomy

Ascaphus truei Stejneger, 1899, Humptulips, Washington, United States.

other common names

None known.

physical characteristics

The dorsum usually is brown or gray with a pale patch on the snout between the eyes and nose. The belly is a translucent pink with scattered small white dots. The toes of the hind feet are short, but the feet are webbed, though slightly less extensively than in Ascaphus montanus. Adults are 1.2–2.0 in (30–50 mm) long; females are slightly larger than the males. The tadpoles are slate gray and up to 1.2 in (30 mm) long; they typically have a white spot on the tip of the tail.

distribution

This frog is distributed along the Pacific coast of North America from the Nass River in British Columbia south through the Coast Ranges and Cascade Range to northwestern California.

habitat

This species inhabits cold, clear, unsilted streams from sea level up to subalpine meadows.

behavior

Elusive and nocturnal and tending to hide under rocks or logs by the stream edge or in little rivulets, these frogs range into the forest on rainy days and in the evenings to forage for food. The tadpoles cling to rocks in fast-flowing currents by means of an enlarged, suction-cup-like mouth that keeps them from being washed away. Small tadpoles tend to be found in pools, and larger tadpoles inhabit riffles; sometimes they can be seen attached to exposed rocks in midstream. Predatory threats are from snakes, fish, larger frogs, birds, invertebrates, and small mammals.

feeding ecology and diet

The frogs' food includes terrestrial and aquatic insects. The tadpoles use their rasping mouthparts to scrape off algae and diatoms from rocks.

reproductive biology

Breeding is in the fall. During mating, inguinal amplexus lasts 24–30 hours; the so-called tail is used for insemination. The sperm remains viable within the female's oviduct until egg laying takes place many months later. Females lay 45–75 unpigmented eggs in small clusters adhering to the underside of rocks in streams. The tadpoles take one to three years to metamorphose. The newly transformed frogs reach sexual maturity in three to five years. These frogs are estimated to live up to 15 years.

conservation status

Not threatened.

significance to humans

The species is interesting because of its primitive morphologic features and unusual life history. The frogs are of some importance because of their reliance upon undamaged forested streams that are generally too small to maintain fish.

Resources

Books

Nussbaum, R. A., E. D. Brodie, and R. M. Storm. Amphibians and Reptiles of the Pacific Northwest. Moscow: University of Idaho Press, 1983.

Wright, A. H., and A. A. Wright. Handbook of Frogs and Toads of the United States and Canada. Ithaca, NY: Comstock, 1949.

Periodicals

Bull, E. L., and B. E. Carter. "Tailed Frogs: Distribution, Ecology, and Association with Timber Harvest in Northeastern Oregon." U.S. Department of Agriculture, Forest Service Research Paper PNW-RP-497 (1996): 1–12.

Bury, R. B., and M. J. Adams. "Variation in Age at Metamorphosis Across a Latitudinal Gradient for the Tailed Frog Ascaphus truei." Herpetologica 55, no. 2 (1999): 283–291.

Daugherty, C. H., and A. L. Sheldon. "Age-Determination, Growth and Life History of a Montana Population of the Tailed Frog (Ascaphus truei)." Herpetologica 38, no. 4 (1982a): 461–468.

Daugherty, C. H., and A. L. Sheldon. "Age-Specific Movement Patterns of the Tailed Frog Ascaphus truei." Herpetologica 38, no. 4 (1982b): 468–474.

Diller, L. V., and L. R. Wallace. "Distribution and Habitat of Ascaphus truei in Streams on Managed, Young Growth Forests in North Coastal California." Journal of Herpetology 33, no. 1 (1999): 71–79.

Dupuis, L., and D. Steventon. "Riparian Management and the Tailed Frog in Northern Coastal Forests." Forest Ecology and Management 124, no. 1 (1999): 35–43.

Nielson, M., K. Lohman, and J. Sullivan. "Phylogeography of the Tailed Frog (Ascaphus truei): Implications for the Biogeography of the Pacific Northwest." Evolution 55, no. 1 (2001): 147–160.

Wallace, R. L., and L. V. Diller. "Length of the Larval Cycle of Ascaphus truei in Coastal Streams of the Redwood Region, Northern California." Journal of Herpetology 32, no. 3 (1998): 404–409.

David M. Green, PhD