Eastern Tailed Frog (Frogs of British Columbia)

Eastern Tailed Frog

Ascaphus montanus

Summary ⁶

The tailed frogs are two species of frogs in the genus Ascaphus, the only taxon in the family Ascaphidae /æˈskæfɪdiː/. The "tail" in the name is actually an extension of the male cloaca. The tail is one of two distinctive anatomical features adapting the species to life in fast-flowing streams. These are the only North American frog species that reproduce by internal fertilization.

Description ⁷

Ascaphus montanus adult males range from 30 to 50 mm in SVL, while the females are slightly larger (Green, 2003). The "tail" (actually an extension of the cloaca used for internal fertilization) is a distinguishing feature of adult males in this genus (Duellman and Trueb, 1994). The head is wide, with nostrils widely spaced (Green, 2003). Pupils are vertical and in the shape of a diamond (Green, 2003). There is a skin fold from the eye back to the corner of the mouth (Green, 2003). The tympanum is not visible (Green, 2003). Dorsally, the skin is tuberculate (Green, 2003). Hind toes are short and webbed, with the outermost toe being thickest (Green, 2003). The lungs are small, with most gas exchange occurring via the skin (Green, 2003). Dorsally, adult Ascaphus montanus frogs are brown on the dorsal surfaces, occasionally with faint black bands extending from the shoulder across the eye and over the nostril to the upper jaw; ventrally, they are whitish (Metter, 1964). There is a pale patch between the eyes, extending forward across the snout (Green, 2003). Breeding males appear to have rougher skin, because the tubercles on the back and legs increase in size during mating season (Metter, 1964). Breeding males also have a line of dense small tubercles along the edge of the lower jaw, and cloacal spines (Metter, 1964). Nuptial pads develop on breeding males, on the inner palmar tubercle and forearm and as a patch on each side of the pectoral region (Metter, 1964).

Ascaphus montanus and A. truei frogs have nine presacral vertebrae. Of these, the third, fourth, and fifth vertebrae bear closely associated but free (not fused) ribs. Among living frog species, these vertebral characteristics are shared only by frogs in the genus Leiopelma; all other frog species have eight or fewer presacral vertebrae, with ribs fused to the vertebrae (Duellman and Trueb, 1994).

Tadpoles are dark slate gray with wide heads, with a large ventral sucker surrounding the mouth, and up to 16 rows of denticles (Green, 2003; Duellman and Trueb, 1994). The larvae are relatively large, growing to 30 mm (Green, 2003). Small glands are scattered over the body (McDiarmid and Altig, 1999). There is a single spiracle, which is located midventrally (McDiarmid and Altig, 1999). The tail tip is rounded, with a white spot bordered by black (Hallock and McAllister, 2005).

Tailed frogs (Ascaphus montanus and Ascaphus truei) are some of the most primitive frogs, along with the genus Leiopelma (Duellman and Trueb, 1994). These frogs all resemble the earliest known frogs from the Jurassic in their skeletal anatomy (Duellman and Trueb, 1994). They retain many primitive morphological features which have been lost in all other living anuran lineages (Ford and Cannatella, 1993).

Ascaphus montanus is found inland while the closely related species Ascaphus truei is distributed along the coast (Nielson et al., 2001). The isolation of the two lineages is thought to date back to the late Miocene or early Pliocene, most likely due to the rise of the Cascade Mountains (Nielson et al., 2001).

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