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Ranidae

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Ranidae is a large family of amphibians commonly known as "true frogs." These animals are highly successful because they have a massive global presence. They are considered cosmopolitan, meaning they are found across the world. In fact, true frogs live on every continent except for Antarctica. Their range includes North America and northern South America. They are also found throughout Europe and Africa, including the island of Madagascar. In Asia, their territory stretches from the East Indies all the way to New Guinea. One specific species, the Australian wood frog, has even spread into the far north of Australia.

Rana ishikawae
Rana ishikawae

Most members of this family share specific physical traits that help them survive. They typically possess smooth and moist skin. To move through their environments, they use large and powerful legs. Their feet are often extensively webbed, which aids in swimming. The size of true frogs varies significantly between different species. For instance, the wood frog is quite small. Other species within the Ranidae family can grow to be very large. While many are aquatic or live very close to water, they occupy many different habitats. Some are arboreal, meaning they live in trees. A few rare species can even survive in brackish water, which is a mix of fresh and salt water.

The life cycle of most true frogs involves a distinct transition. Most species lay their eggs directly in the water. Once the eggs hatch, the young undergo a tadpole stage. This process allows them to live in aquatic environments before reaching adulthood. This developmental path is common to most frog families. However, the family Ranidae shows incredible variation in where these life stages take place. This flexibility allows them to inhabit many different ecological niches around the globe.

Scientists are still researching the evolutionary history of the Ranidae. There are different theories about where they first began. One theory suggests they had Gondwanan origins. This idea proposes they evolved on Insular India during the Cretaceous period. Under this theory, they stayed in the Indian subcontinent until the late Eocene. When India collided with Asia, the frogs could colonize Eurasia and the rest of the world. However, more recent studies suggest a different path. These studies propose that the Ranidae actually originated in Eurasia. They suggest that related lineages colonized India from Eurasia during the Paleogene period.

Understanding the exact relationship between these frogs and others is complex. The Ranidae are related to several other families, such as Rhacophoridae and Dicroglossidae. Some researchers believe they are most closely related to Nyctibatrachidae, a group found only in India. These two groups may have diverged during the early Eocene. Other studies, however, suggest a closer link to the Dicroglossidae family. The Ranidae began to spread out of Asia at the end of the Eocene. By the beginning of the Miocene, they had successfully colonized almost every continent.

Modern science is still working to organize the many groups within Ranidae. This process is called systematics, and it involves classifying organisms into groups. The subdivisions of Ranidae are currently a matter of scientific dispute. Many former subfamilies have been moved into their own separate families. These include Petropedetidae, Cacosterninae, Mantellidae, and Dicroglossidae. The genus Rana, which was once very large, has been split into much smaller groups. Today, scientists recognize many different genera. For example, the genus Amolops contains 80 different species. The genus Odorrana is also large, with 64 species. Other groups are much smaller, like the genus Huia, which contains only one species.

Rana curtipes
Rana curtipes

Because there is so much diversity, some classifications remain uncertain. In 2023, one group of experts tentatively moved several genera into the genus Hylarana. These included Amnirana, Chalcorana, Humerana, Hydrophylax, Indosylvirana, Papurana, Pulchrana, and Sylvirana. They did this to clear up taxonomic confusion. However, other organizations like AmphibiaWeb do not recognize these changes. Some species are even placed in a category called incertae sedis. This term is used when a species' taxonomic status is too uncertain for specific placement. This constant movement in scientific naming shows how much we are still learning about these animals.

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File:Rana ishikawae.jpg
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