The Nasikabatrachus sahyadrensis, more commonly known as the purple
frog, pig-nosed frog, Jurassic frog, or the coelacanth of frogs
was first officially discovered in 2003. It is the first new frog
species to be named to a new family since 1926. The new family,
Nasikabatrachidae, joins the other 28 known families.
The species name Nasikabatrachus sahyadrensis comes from various
words in Sanskrit, a classical language of India. “Nasika” means
“nose”, “batrachus” meaning “frog” and "Sahyadri” meaning Western
Ghats, which is the mountain range in India where the frog is
located.
Distribution
The purple frog is endemic to the Western Ghats mountain range in
southern India. As of 2006 it is known from only two locations, both in
Idukki District in the Cardomom Hills in Kerala; Kattapana and
near Idukki town.
Habitat
Purple frogs have been found in secondary forest contiguous with
montane evergreen forest. The altitudinal range it is found in is
850-1,000 meters above sea level. It has been found in
subtropical/tropical moist lowland and montane, inland wetlands such as
marshes and pools, as well as canals and ditches. It requires fairly
loose, damp, well-aerated soil, preferably in close proximity to
termite colonies, to burrow into. The Western Ghats mountains where the
purple frog is found is considered by conservationists to be a
biodiversity hotspot; a rich but threatened reservoir of unique plant
and animal life
Physical Description
The type specimen for the physical description of the purple frog
was an adult female collected in 2000 by S. D. Biju. The purple frog is
a relatively large frog with a generally bloated appearance. An adult
purple frog will reach about 7 cm in length, but females tend to be
larger than males. Its skin is smooth, yet thick and has a blackish
purple coloration. The head is short and small in comparison to the
rest of its body and is pointed. The snout is tapered to a knob-like
white protuberance, which is the reason for one of its common names –
pig-nosed frog. The eyes of the frog are small with a black iris and
rounded, horizontal pupil. It has prominent upper eyelids, but the
lower eyelids are merely integumentary folds. The mouth is small and
ventral, with a narrow gape and contains a small, basally attached and
fluted tongue. The fore limbs are short and end in rudimentarily webbed
feet with the tips of the fingers being rounded without disks. The hind
limbs are small and short, with the toes being three-quarters webbed
and rounded at the tips without disks. Each hind foot also possesses a
large, elongated, white shovel-like inner metatarsal tubercle, which
is used for digging.
The skeleton of the purple frog is characteristic of a burrowing
frog and displays bones with a “well-calcified cortical area, a skull
with strongly ossified neurocranial and dermal elements, a short
tibiale and fibulare, strong and short tibiofibular bones, and a well
developed and highly calcified prehallux”1.
Reproduction
The purple frog only breeds a few weeks a year during the monsoon
season. During mating they have a repetitive loud call consisting of
single notes of ‘rraaak’. The frogs can be heard calling from 3 to 4 cm
beneath the ground and emerge during the night to breed. They often
breed in ponds that are close to streams, as well as temporary and
permanent ponds and ditches. During mating, the purple frog shows
inguinal amplexus, which is where the male clasps the female from
behind just above the legs. The bloated shape of both male and female
purple frogs, and the smaller size of the male, may mean that males
partially glue themselves onto females using sticky skin secretions.
The eggs are laid in water, often ponds close to streams, and hatch
into tadpoles.
Lifestyle
The purple frog lives a very reclusive, fossorial (digging or
burrowing) lifestyle. It spends most of its life 1.3-3.7m below the
ground and only comes to the surface for a few weeks a year during the
monsoon season to breed before it disappears again
Behavior
Digging is the primary behavior exhibited by the purple frog other
than living underground almost full time. Purple frogs can dig
themselves completely into the ground if the soil is right within 3 to
5 minutes. If the frog finds itself on an unsuitable surface for
digging, such as hard ground, pebbled- or gravel-strewn soil, or areas
with a thick mat of weeds, they will go in search of cover and a more
effective place to burrow. To burrow downwards, the purple frog assumes
a squatting position and uses it strong hind feet like spades to push
the soil from underneath itself over to the back of its body. After
digging they rest underground in a horizontal position with their limbs
tucked under their body, but not for long. They do not remain idle
underneath the soil for long periods of time, especially when they are
foraging for prey.
Diet
The diet of the purple frog mainly consists of soil termites. Since
it lives underground for the majority of its life, it is a fully
capable underground forager. Due to the nature of the anatomy of its
mouth, which is narrow with a small gape, it cannot catch and consume
larger prey. But the anatomy of its head, a strong and pointed snout,
allows it to penetrate underground termite nests. Other than termites,
it mostly eats ants and small worms.
Conservation Status
The main threat to the purple frog is forest loss due to expanding
cultivation of coffee, cardamom, ginger, and other crops. The forest
coverage in the Western Ghats has been reduced to less than 10 percent
of its original extent due to human pressure from agriculture. The
remaining 10 percent is remote and fairly inaccessible which is one
reason the frog has gone undiscovered for so long. Its IUCN Red List
Status is endangered as of 2004 because its “Extent of Occurrence is
less than 5,000 km2, all individuals are in fewer than five locations,
and there is continuing decline in the extent and quality of its
habitat in the Cardomom Hills”. The species is thought to be declining
in numbers, but it is difficult to accurately determine how many exist
since it is so hard to find. There have only been 135 specimens
observed since it was first classified as a new species of frog and
only three of them have been female. It has not yet been observed in
any protected areas within its known habitat, such as the nearby
Silent Valley National Park.
Interaction with humans
The purple frog does not have much interaction with or impact on
humans. The only time humans have ever seen it is when it comes above
ground during the monsoon season to breed. Humans are destroying its
habitat, so if scientists are going to continue studying the purple
frog, the protection of their forest habitat is an urgent priority.
How the species relates to ancient fossil forms
The purple frog is a true “living fossil” and is the only
surviving member of the ancient amphibian family Nasikabatrachidae. Its
closest living relatives are found in the Seychelles, near Madagascar
1,800 miles away, in the Sooglossidae family. India and the
Seychelles were once a part of the same landmass, but were separated
about 65 million years ago. From a phylogenetic analysis done by S. D.
Biju and Franky Bossuyt, the discoverers of the purple frog, it is
estimated that the origin of the Sooglossidae/Nasikabatrachidae lineage
occurred around 182 million years ago. The relationship between the
purple frog and the Sooglossidae in the Seychelles suggests that these
frogs diverged from a common ancestor about 130 million years ago
before the ancient landmass Gondwana broke apart. The two families of
frogs are similar, yet they differ in both molecular genetics and
morphology. It is estimated that both families became isolated from
Neobatrachia (the “new” or “higher” frogs) during the Middle/Late
Jurassic and Early Cretaceous periods, which is around the time that
Gondwanaland broke up. The discovery of the purple frog has also
revived the idea of there being a prehistoric land bridge between
Africa and India that might have been a dispersal corridor for animals
between the two countries. There are many ideas about how the
Sooglossidae and Nasikabatrachidae got separated, but so far there is
no definite explanation.
1Biju, S. D. and Bossuyt, Franky. “New frog family from
India reveals an ancient biogeographical link with the Seychelles”.
2003, October 16. Nature. Vol. 425, p. 711-714.
Dutta, S. K.
et al. “Jurassic frogs and the evolution of amphibian endemism in the
Western Ghats”. 2004, January 10. Current Science. Vol. 86, No. 1,
p. 211-216.
Hedges, S. Blair. “The Coelacanth of Frogs”. 2003, October 16. Nature. Vol. 425, p. 669-670.
“Nasikabatrachus
sahyadrensis”. Global Amphibian Assessment. 2006. IUCN, Conservation
International, and NatureServe.
<http://www.globalamphibians.org/servlet/GAA?searchName=Nasikabatrachus+sahyadrensis>
“Purple
Frog (Nasikabatrachus sahyadrensis)”. EDGE of Existence. 2006.
Zoological Society of London.
<http://www.edgeofexistence.org/amphibians/species_info.php?id=549>.
Radhakrishnan, C. et al. “Extension of range of distribution
of Nasikabatrachus sahyadrensis Biju & Bossuyt (Amphibia: Anura:
Nasikabatrachidae) along Western Ghats, with some insights into its
bionomics”. 2007, January 25. Current Science. Vol. 92, No. 2, p.
213-216.
Reisman, Elizabeth. “AmphibiaWeb - Nasikabatrachus sahyadrensis”. 2008. AmphibiaWeb. <http://amphibiaweb.org/>.
Roach,
John. “Frog Discovery Is “Once in a Century””. National Geographic
News. 2003, October 15. National Geographic.
<http://news.nationalgeographic.com/news/2003/10/1015_031015_purplefrog.html>.
Ruder,
Kate. “Purple Frog Pops Up”. 2003, October 17. Genome News Network.
<http://www.genomenewsnetwork.org/articles/10_03/purple_frog.shtml>.