Comprehensive DescriptionRead full entry
Nasikabatrachus sahyadrensis is a relatively large burrowing frog with a distinct, bloated appearance. Snout-vent length ranges from 52.8 mm to 89.9 mm (Radhakrishnan et al. 2007). Males are about one third the size of females (Zachariah et al. 2012). The head is small and relatively short in comparison with the rest of the body. The snout ends in a white, knob-like protrusion. The mouth is ventral, with a narrow gape. The upper jaw is rigid while the lower jaw is flexible and flaplike, enabling a grooved aperture to be formed through which the tongue can be protruded. The tongue is basally attached, small and fluted, with a rounded tip. Maxillary teeth are absent. Eyes are small, with a prominent upper eyelid and a lower eyelid consisting of a small skinfold. Males have a single subgular vocal sac (Zachariah et al. 2012). The tympanum is lacking. Both the forelimbs and hindlimbs are short. Palms are hard with rounded fingertips (but no discs) and barely webbed fingers. Feet have rounded toe tips (no discs) and are 3/4 webbed. Each hindfoot possesses a large, white, shovel-like inner metatarsal tubercle, used for digging. Irises are black, with a rounded, horizontal pupil. This species has smooth, black skin dorsally which fades into gray ventrally (Biju and Bossuyt 2003; Radhakrishnan et al. 2007).
The skeletal structure of N. sahyadrensis is characteristic of a burrowing frog, with a strongly ossified skull and well-calcified bones. Due to the species' unique appearance, as well as specific osteological differences, Biju and Bossuyt (2003) placed N. sahyadrensis in a new anuran family, named Nasikabatrachidae. Although some traits are shared with the sister group, Sooglossidae, the authors concluded the lack of toe discs and much larger size, as well as other characters, significantly separate N. sahyadrensis from Sooglossidae (Biju and Bossuyt 2003).
N. sahyadrensis tadpoles have a wide, flattened, wedge shaped snout. The nostrils are located on top of the head, closer to the eyes than the snout tip. Eyes are small and located dorsolaterally. The oral disc is suctorial and ventrally located. Body is wide and flattened. The tail is low relative to the body, dorsal and ventral fins are about the same height. The tail is about two thirds of the total length. The dorsum is dark brown, while the ventral surface is a silvery cream color. The eyes are black. The tail is light brown, with dark brown patches throughout (Raj et al. 2012).
The species authorities for N. sahyadrensis are S.D. Biju and F. Bossuyt.
N. sahyadrensis tadpoles were first described in Annandale (1918), without specimens of adults. It was tentatively assigned to the family Cystignathidae (Raj et al. 2012).
In Sanskrit, nasika means "nose" and batrachus means "frog," while Sahyadri refers to the location where this species is found (the Western Ghats, also known as the Sahyadri Mountains, a low-lying mountain range along the west coast of the Indian subcontinent).
As pointed out by Hedges (2003), most of the anuran families were named in the mid-nineteenth century; the last time the discovery of a new species led to the description of a new family was in 1926 (Frost 2003). Based on a phylogenetic analysis of mitochondrial genes, Biju and Bossuyt (2003) suggest that this species, endemic to India, is a sister taxon to the Sooglossidae, a family of frogs endemic to the Seychelles Islands. This has lent support to the idea of a possible land bridge between Africa and India, enabling faunal dispersal. The species Nasikabatrachus sahyadrensis is estimated to have originated in the Jurassic, 130-180 million years ago (Biju and Bossuyt 2003; Dutta et al. 2004) which is 50 to 100 million years earlier than any other known frog species in India (Aggarwal 2004), and predating the breakup of the ancient continent Gondwana (Radhakrishnan et al. 2007; Dutta et al. 2004).