Frog

A frog is a type of amphibian that belongs to the group called Anura. Frogs have short bodies and no tails. They are found everywhere, from the tropics to subarctic areas, but many live in tropical rainforest and wetlands. Frogs make up most of all living amphibian species.

Adult frogs have strong bodies, big eyes, and long tongues. They can live in fresh water, on land, in trees, or even underground. Their skin comes in many colors, which helps them hide or warn others. Frogs make many different vocalisations, especially to find a mate.

Frogs start life as eggs in water. These eggs hatch into swimming tadpoles. Tadpoles grow and change, or metamorphose, into adult frogs. Adult frogs eat small animals, mostly insects, using their sticky tongues. They help nature by eating pests and being food for bigger animals.

Frogs are also important to humans. In some places, people eat frog legs, and frogs often appear in stories and symbols. Many frog species are in danger because of diseases and changes to their homes. Scientists are working to protect these amazing animals.

Etymology and taxonomy

All animals in the order Anura are called frogs. Only members of the family Bufonidae are called "true toads". The words "frog" and "toad" describe where the animals live and how they look, not their family relation. Frogs usually live in water or near it and have smooth skin. Toads live on land and have dry, warty skin. But there are many exceptions.

The name "Anura" comes from Ancient Greek and means "tailless". This name refers to the fact that these amphibians do not have tails. The word "frog" may come from old English words related to jumping, but its origin is not certain. The word "toad" also has an unclear origin.

Evolution

Scientists are still figuring out how frogs are related to other amphibians. Studies show that salamanders and caecilians might be closer to each other than to frogs. This split happened long ago, in the Paleozoic or early Mesozoic era, before Pangaea broke apart.

In 2008, scientists found a fossil called Gerobatrachus hottoni in Texas. It lived 290 million years ago and had features of both frogs and salamanders. They also found early frog relatives like Triadobatrachus massinoti from Madagascar and Czatkobatrachus polonicus from Poland, dating back about 250 million years. These early frogs looked a bit like today's frogs but had longer bodies and more vertebrae. True frogs, such as Prosalirus bitis from the early Jurassic period, appeared around 199 million years ago. These frogs had lost most of their tails and were better at jumping. By the Jurassic period, modern frogs were probably fully evolved.

Frog fossils have been found on every continent. For example, 40 million-year-old helmeted frog fossils were found in Seymour Island on the Antarctic Peninsula. These frogs were related to those in South American Nothofagus forests today.

Morphology and physiology

Frogs have no tails, except when they are very young. Most frogs have long back legs, webbed feet, big eyes, and skin that can be smooth or bumpy. They come in many sizes, from very small to quite large.

A frog's legs and feet change depending on where it lives—on the ground, in water, in trees, or underground. Frogs need to move fast to catch food and stay safe. Many frogs can jump far because their legs and muscles are made for leaping.

Frogs have skin that helps protect them, control their temperature, and let them breathe. Their skin can take in water and oxygen, but it can also dry out. Some frogs have special skin to help them blend in or keep water in.

Frogs can breathe through their skin and also have lungs. Some water frogs have no lungs and use only their skin to breathe. Frogs have a three-chambered heart, which helps mix oxygen-rich and oxygen-poor blood.

Frogs catch food with their sticky tongue, which they can shoot out fast to grab insects. They have small teeth on the top jaw to hold food, but these teeth are weak and not used for chewing.

In female frogs, eggs move through organs called ovaries and oviducts to the outside. Male frogs have organs called testes, and they put sperm on the eggs when they mate. The male climbs on the back of the female in a position called amplexus to release sperm over the eggs.

Locomotion

Frogs move in many ways, like jumping, running, walking, swimming, burrowing, climbing, and gliding. They are famous for how far they can jump. The striped rocket frog can jump more than fifty times its own body length!

Frogs move differently depending on where they live. Some frogs, like the red-legged running frog, run instead of jump. Others, like the purple frog, dig homes underground. Tree frogs can climb and even glide through the air using skin flaps on their legs.

Life history

Frogs have two main ways of reproducing: prolonged breeding and explosive breeding. In prolonged breeding, frogs gather at ponds, lakes, or streams to breed at certain times of the year. Many return to the same water where they started life as larvae. In explosive breeding, frogs arrive at breeding sites quickly when triggered by things like rain in dry areas. Mating and egg-laying happen fast so the young can grow quickly before the water dries up.

Males usually arrive first at breeding sites and stay there, while females come later and leave after laying eggs. Females often choose mates based on the depth of their calls.

When females lay eggs, the male grabs the female and holds her tightly. The female releases eggs and the male puts sperm on them; this happens in the water. A few special frogs give birth to live young instead of laying eggs. These include some West African frogs and a few others from Tanzania and Chile.

Frogs lay their eggs in different ways—clumps, films on the surface, strings, or singly. Some lay eggs in water, others on land. For example, the yellow-striped pygmy eleuth lays eggs singly in moist soil, while the red-eyed treefrog lays eggs on leaves above water, and the tadpoles drop into the water below.

The young frogs, called tadpoles, hatch from eggs. Tadpoles don’t have eyelids or limbs and have gills and tails for swimming. They change into adult frogs in a process called metamorphosis. During this change, they develop lungs, lose their gills, grow legs, and their bodies change to be ready for life as adult frogs.

Adult frogs live near water but are not fully aquatic. Most eat small animals like insects, spiders, and worms. Some larger frogs eat other frogs, small mammals, or fish. A few eat plants too. Frogs catch their food with sticky tongues or by grabbing it with their mouths. They are eaten by many animals, including birds, snakes, and other frogs.

Frogs play an important role in nature because they eat many insects, helping to control their numbers and support plant growth. They are also food for many larger animals.

Some frogs care for their young. For example, the strawberry poison-dart frog lays eggs on the forest floor, and the male keeps them moist. When they hatch, the female carries the tadpoles to small pools. Other frogs guard their eggs or carry them in special ways to keep them safe until they can develop into adult frogs.

Defence

Frogs may look fragile because they are small and don’t have sharp teeth or spines, but they have many smart ways to protect themselves. Many frogs hide by blending into their surroundings with their spotted or streaked skin. Others can jump very far, often into water, to get away from danger.

Many frogs have special glands that make toxins. These toxins can make predators feel sick, so they learn to stay away from those frogs. Some poisonous frogs, like the poison dart frogs, have bright colors to warn predators about their toxicity. Other frogs use tricks like puffing up their bodies or making loud noises to scare off attackers. Even with predators around, many frogs know how to stay safe.

Distribution

Frogs live on every continent except Antarctica, though some islands do not have them. They are most diverse in warm places, like rainforests, compared to cooler areas such as Europe. Some frogs live in dry places, like deserts, and have special ways to survive. For example, frogs in the Australian genus Cyclorana bury themselves underground and wait for rain to come out and breed. Other frogs, like the wood frog (Rana sylvatica), live in very cold areas, such as the Arctic Circle, and can survive freezing temperatures by freezing parts of their bodies.

Conservation

See also: Decline in amphibian populations

Frog numbers have gone down a lot since the 1950s. Many frog species are in danger and some have disappeared. This happens because of things like losing their homes, pollution, and changes in the weather.

Frogs are good for showing us if the environment is healthy because they are very sensitive to changes. Some places are working to save frogs by breeding them in special places.

Human uses

Culinary

Frog legs are eaten in many parts of the world. Indonesia is the largest exporter of frog meat. Frog farming has become important because wild frog populations decreased.

Scientific research

See also: Animal testing on frogs and Frogs in captivity

Frogs have been important in scientific research. In 1970, NASA sent two bullfrogs into space. Frogs are often used in schools for dissections, though this practice is decreasing due to concerns about animal welfare. Scientists have also used frogs to study electricity, heart function, and cloning. The African clawed frog helped scientists understand pregnancy and develop cloning techniques.

Pharmaceutical

Frog toxins interest scientists. Some toxins from frogs could help develop new medicines, including possible treatments for diseases like HIV.

Cultural significance

Frogs appear in many stories and cultures. In Chinese myths, a giant frog tries to swallow the moon during a lunar eclipse. Ancient Egyptians had a frog-shaped god named Heqet who protected newborns. In the Bible, Moses brought a plague of frogs to the Egyptians. Frogs also appear in fairy tales like The Frog Prince and in popular culture, such as Kermit the Frog and the game Frogger.