Wednesday, 20 February 2013

Cute Pictures Of Frogs

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Cute Pictures Of Frogs Biography
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, but molecular 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, making them among the most diverse vertebrate groups.
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. 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. Frog warts are elevations in the skin where glandular toxins tend to concentrate. 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 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 frogs 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 around the world have declined significantly since the 1950s. More than one third of species are considered to be threatened 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.The name frog derives from Old English frogga, abbreviated to frox, forsc and frosc, probably deriving from Proto-Indo-European preu = "to jump".[2] Approximately 88% of amphibian species are classified in the order Anura.[3] These include around 4,810 species in 33 families, of which the Leptodactylidae (1,100 spp.), Hylidae (800 spp.) and Ranidae (750 spp.) are the richest in species.[3]
European fire-bellied toad (Bombina bombina)
The use of the common names "frog" and "toad" has no taxonomic justification. From a classification perspective, all members of the order Anura are frogs, but only members of the family Bufonidae are considered "true toads". The use of the term "frog" in common names usually refers to species that are aquatic or semi-aquatic and have smooth, moist skins; the term "toad" generally refers to species that are terrestrial with dry, warty skins.[4][5] There are numerous exceptions to this rule. The European fire-bellied toad (Bombina bombina) has a slightly warty skin and prefers a watery habitat[6] whereas the Panamanian golden frog (Atelopus zeteki) is in the toad family Bufonidae and has a smooth skin.[7]
Anura includes all modern frogs and any fossil species that fit within the anuran definition. The characteristics of anuran adults include: nine or fewer presacral vertebrae, a long and forward sloping ilium, the presence of a urostyle, no tail, shorter forelimb than hindlimb, radius and ulna fused, tibia and fibula fused, elongate ankle bones, absence of a prefrontal bone, presence of a hyoid plate, a lower jaw without teeth, an unsupported tongue, lymph spaces underneath the skin and a muscle, the protractor lentis, attached to the lens of the eye.[8] The anuran larva or tadpole has a single central respiratory spiracle and mouthparts consisting of keratinous beaks and denticles.[8]
Panamanian golden frog (Atelopus zeteki)
Frogs and toads are broadly classified into three suborders: Archaeobatrachia, which includes four families of primitive frogs; Mesobatrachia, which includes five families of more evolutionary intermediate frogs; and Neobatrachia, by far the largest group, which contains the remaining 24 families of modern frogs, including most common species found throughout the world. Neobatrachia is further divided into the two superfamilies Hyloidea and Ranoidea.[9] This classification is based on such morphological features as the number of vertebrae, the structure of the pectoral girdle and the morphology of tadpoles. While this classification is largely accepted, relationships among families of frogs are still debated.[10]
Some species of anurans hybridize readily. For instance, the edible frog (Pelophylax esculentus) is a hybrid between the pool frog (Pelophylax lessonae) and the marsh frog (Pelophylax ridibundus).[11] The fire-bellied toads Bombina bombina and Bombina variegata are similar in forming hybrids. These are less fertile than their parents, giving rise to a hybrid zone where the hybrids are prevalent.[12]
Evolution
The origins and evolutionary relationships between the three main groups of amphibians is hotly debated. A molecular phylogeny based on rDNA analysis dating from 2005 suggests that salamanders and caecilians are more closely related to each other than they are to frogs and that the divergence of the three groups took place in the Paleozoic or early Mesozoic before the breakup of the supercontinent Pangaea and soon after their divergence from the lobe-finned fish. This would help account for the relative scarcity of amphibian fossils from the period before the groups split.[13] Another molecular phylogenetic analysis conducted about the same time concluded that lissamphibians first appeared about 330 million years ago and that the temnospondyl-origin hypothesis is more credible than other theories. The neobatrachians seemed to have originated in Africa/India, the salamanders in East Asia and the caecilians in tropical Pangaea.[14] Other researchers, while agreeing with the main thrust of this study, questioned the choice of calibration points used to synchronise the data. They proposed that the date of lissamphibian diversification be put in the Permian, rather less than 300 million years ago, a date that is in better agreement with the palaeontological data.[15] A further study in 2011 using both extinct and living taxa sampled for morphological as well as molecular data came to the conclusion that Lissamphibia is monophyletic and that it should be nested within Lepospondyli rather than within Temnospondyli. The study postulated that Lissamphibia originated no earlier than the late Carboniferous, some 290 to 305 million years ago. The split between Anura and Caudata was estimated as taking place 292 million years ago, rather later than most molecular studies suggest, with the caecilians splitting off 239 million years ago.[16]
A fossilized frog from the Czech Republic, possibly Palaeobatrachus gigas
In 2008, a fossil of Gerobatrachus hottoni, a stem anuran with many salamander-like characteristics, was discovered in Texas. It dated back 290 million years and was hailed as a missing link, a common ancestor of frogs and salamanders. It seemed to indicate that frogs and salamanders are more closely related to each other than they are to caecilians.[17][18] Before that, the earliest known proto-frog was Triadobatrachus massinoti, from the 250 million-year-old early Triassic of Madagascar.[19] Its skull is frog-like, being broad with large eye sockets, but the fossil has features diverging from modern frogs. These include a longer body and more vertebrae. The tail has separate vertebrae unlike the fused urostyle or coccyx found in modern frogs. The tibia and fibula bones are also separate, making it probable that Triadobatrachus was not an efficient leaper.[19]
Salientia (Latin salere (salio), "to jump") is a stem group including modern frogs in the order Anura and their close fossil relatives the "proto-frogs" (e.g., Triadobatrachus and Czatkobatrachus). The common features possessed by the "proto-frogs" in the Salientia group include fourteen presacral vertebrae (modern frogs have eight or nine), a long and forward-sloping ilium in the pelvis, the presence of a frontoparietal bone and a lower jaw without teeth. The earliest frog fossil that falls into the anuran lineage proper, Prosalirus bitis, lived in the early Jurassic.[4][20] It was discovered in 1995 in the Kayenta Formation of Arizona and dates back to the Early Jurassic epoch (199.6 to 175 million years ago), making Prosalirus somewhat more recent than Triadobatrachus.[21] Like the latter, Prosalirus did not have greatly enlarged legs but had the typical three-pronged pelvic structure of modern frogs. Unlike Triadobatrachus, Prosalirus had already lost nearly all of its tail[22] and was well adapted for jumping.[23]
The earliest known "true frog" is Vieraella herbsti, from the Early Jurassic. It is known only from the dorsal and ventral impressions of a single animal and was estimated to be 33 mm (1.3 in) from snout to vent. Notobatrachus degiustoi from the middle Jurassic is slightly younger, about 155–170 million years old. The main evolutionary changes in this species involved the shortening of the body and the loss of the tail. It is likely that the evolution of modern Anura was complete by the Jurassic period. Since then, evolutionary changes in chromosome numbers have taken place about twenty times faster in mammals than in frogs, which means that speciation is occurring more rapidly in mammals.[24]
An early, well-preserved fossil of Sanyanlichan, which lived 125 million years ago, was found in China in 2001.[25] It had all the characteristics of modern frogs but there were nine presacral vertebrae in its backbone instead of the eight found in present-day species. It is believed to be the ancestor of modern discoglossid frogs such as the midwife toad (Alytes) and the fire-bellied toad (Bombina).[26] Frog fossils have been found on all continents except Antarctica but biogeographic evidence suggests they also inhabited Antarctica in an earlier era when the climate was warmer
Cute Pictures Of Frogs Biography
Cute Pictures Of Frogs Biography
Cute Pictures Of Frogs Biography
Cute Pictures Of Frogs Biography
Cute Pictures Of Frogs Biography
Cute Pictures Of Frogs Biography
Cute Pictures Of Frogs Biography
Cute Pictures Of Frogs Biography
Cute Pictures Of Frogs Biography
Cute Pictures Of Frogs Biography
Cute Pictures Of Frogs Biography

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