Frog
From Wikipedia, the free encyclopedia
For other uses, see Frog (disambiguation).
Frog
Temporal range: Early Triassic-
Holocene, 2500Ma
Pre
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S
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C
P
T
J
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Pg
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Various types of frogs.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Clade: Salientia
Order: Anura
Dumril, 1806 (as
Anoures)
Suborders
Archaeobatrachia
Mesobatrachia
Neobatrachia
List of Anuran families
Native distribution of frogs (in green)
Frogs are a diverse and largely carnivorous group of short-bodied,
tailless amphibians composing the order Anura(Ancient Greek an-
, without + oura, tail). The oldest fossil "proto-frog" appeared in
the early Triassic of Madagascar, butmolecular clock
dating suggests their origins may extend further back to
the Permian, 265 million years ago. Frogs are widely distributed,
ranging from the tropics to subarctic regions, but the greatest
concentration of species diversity is found in tropical rainforests.
There are approximately 4,800 recorded species, accounting for
over 85% of extant amphibian species. They are also one of the five
most diverse vertebrate orders.
The body plan of an adult frog is generally characterized by a stout
body, protruding eyes, cleft tongue, limbs folded underneath and the
absence of a tail in adults. Besides living in fresh water and on dry
land, the adults of some species are adapted for living underground
or in trees. The skin of the frog is glandular, with secretions ranging
from distasteful to toxic. Warty species of frog tend to be
called toads but the distinction between frogs and toads is based on
informal naming conventions concentrating on the warts rather
than taxonomy or evolutionary history; some toads are more closely
related to frogs than to other toads. Frogs' skins vary in colour from
well-camouflaged dappled brown, grey and green to vivid patterns
of bright red or yellow and black to advertise toxicity and warn off
predators.
Frogs typically lay their eggs in water. The eggs hatch into
aquatic larvae called tadpoles that have tails and internal gills. They
have highly specialized rasping mouth parts suitable
for herbivorous, omnivorous or planktivorous diets. The life cycle is
completed when they metamorphose into adults. A few species
deposit eggs on land or bypass the tadpole stage. Adult frogs
generally have a carnivorous diet consisting of small invertebrates,
but omnivorous species exist and a few feed on fruit. Frogs are
extremely efficient at converting what they eat into body mass,
which makes them an important food source for predators. Frogs
are a keystone group in the food web dynamics of many of the
world's ecosystems. The skin is semi-permeable, making them
susceptible to dehydration, so they either live in moist places or
have special adaptations to deal with dry habitats. Frogs produce a
wide range of vocalizations, particularly in their breeding season,
and exhibit many different kinds of complex behaviours to attract
mates, to fend off predators and to generally survive.
Frog populations have declined significantly since the 1950s. More
than one third of species are considered to
bethreatened with extinction and over one hundred and twenty are
believed to have become extinct since the 1980s.
[1]
The number of
malformations among frogs is on the rise and an
emerging fungal disease, chytridiomycosis, has spread around the
world. Conservation biologists are working to understand the
causes of these problems and to resolve them. Frogs are valued as
food by humans and also have many cultural roles in literature,
symbolism and religion.
Contents
[hide]
1 Etymology and taxonomy
2 Evolution
3 Morphology and physiology
o 3.1 Feet and legs
o 3.2 Skin
o 3.3 Respiration and circulation
o 3.4 Digestion and excretion
o 3.5 Reproductive system
o 3.6 Nervous system
o 3.7 Sight
o 3.8 Hearing
o 3.9 Call
o 3.10 Torpor
4 Locomotion
5 Life history
o 5.1 Reproduction
o 5.2 Life cycle
5.2.1 Eggs / frogspawn
5.2.2 Tadpoles
5.2.3 Metamorphosis
5.2.4 Adults
o 5.3 Parental care
6 Defence
7 Distribution and conservation status
8 Uses
9 Cultural beliefs
10 References
o 10.1 Notes
o 10.2 Bibliography
11 External links
