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Rabb’s Fringe-limbed Treefrog

Central America

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Ecnomiohyla rabborum

Endangered

There is some ongoing forest clearing within the species' range for the development of luxury holiday homes. Urban development remains an ongoing threat as it is fragmenting and degrading the forest, and conifer plantations are replacing the natural habitat required by the species.

Ecnomiohyla rabborum, commonly known as Rabbs' fringe-limbed treefrog, is a critically endangered species of frog in the family Hylidae; mounting evidence suggests that E. rabborum is probably extinct. They were relatively large frogs that inhabited the forest canopies of central Panama. Like other members of the genus Ecnomiohyla, they were capable of gliding by spreading their enormous and fully webbed hands and feet during descent. The males of the species were highly territorial and would guard water-filled tree holes used for breeding. They were also the ones responsible for guarding and caring for the young, including providing food. They were the only known species of frog where the tadpoles derived nutrition by feeding on the skin cells of their fathers.

Ecnomiohyla rabborum was a relatively large frog. The snout-vent length (SVL) of males averaged between 62 to 97 mm (2.4 to 3.8 in), while in females it was between 61 to 100 mm (2.4 to 3.9 in). The head was wider than the body and flattened at the top. The snout was moderately long with nostrils protruding from the sides near the tip. Viewed from the top, the snout was more or less elliptical in shape. The canthal ridge was concave (curves outward) and had thick and rounded edges. The loreal regions were similarly concave. The tympana was smaller in diameter than the eyes and slightly inclined. Smooth glandular structures (known as the supratympanic fold) extended over the tympana from the eyes to the edges of the lower jaw. The tongue was round, and the species possessed narrowly spaced ovoid groups of pre-vomerine teeth. The arms were short and stout with very large hands. There were no skin folds on the wrists, though a scalloped fringe of skin was present from the elbows to just below the discs on the fourth fingers. The fingers were all relatively short with large flattened discs on the tips. The discs on the second, third, and fourth fingers were about the same diameter as the tympana. Small protrusions known as tubercles were present on the underside of the hands. On the first finger, the tubercles on the tipmost joints were elliptical in shape. On the second and third fingers, the tubercles below the finger joints (subarticular tubercles) were smaller than that on the fourth fingers. There were no tubercles on the palms of the hands though elongated flat tubercles were present behind the bases of the inner fingers (the "thumbs"). Numerous small and round tubercles were also present in between the joints of the fingers. The fingers were more or less fully webbed.

The hind limbs were slender and of moderate length. Like the hands, the feet were very large. When resting, the heels of the legs barely overlapped each other. If stretched forward up the length of the body, the tibiotarsal articulation (the "ankle") would reach beyond the eyes. Like the arms, a fringe of scalloped skin also extended from the heel to the base of the foot on each leg, continuing as a low ridge to the base of the disc of the fifth toe. The toes, like the fingers, possessed flattened discs at the tips, though they were slightly smaller in diameter. The tubercles on the tipmost joints of the fifth toes were larger than all of the other subarticular tubercles on the toes. Interspersed between them were numerous small and conical tubercles. The toes were also fully webbed.

The skin of E. rabborum was granular in texture and predominantly a mottled brown. The upper surfaces of the limbs was also mottled brown while the rear surfaces of the thighs were a pale yellow. The chin and upper chest was distinctively brown, though the rest of the underside of the body was mostly white speckled with irregular brown spots. The eyelids and upper surfaces of the limbs and back were studded with green flecks, the appearance and positions of which could be changed by the animal voluntarily (metachrosis). The irises of the eyes was uniformly reddish brown. During the breeding season, adult males of the species were characterized by greatly enlarged upper arms (humerus) with a bony ridge covered by skin and black keratinized spines. Spines were also present on the upper surface of the area just before the thumbs. These spines were likely used during amplexus.