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The earliest amphibians were all internal fertilizers. It was not until 300 million years ago that the Anura (early internal fertilizer) and Caudata (early external fertilizer) orders had begun. Most anurans now externally fertilize. Anurans are the amphibians lacking a tail such as frogs and toads. Anurans are commonly used as a model organism for amphibians, because of the large, easy to manipulate eggs, fast developmental rate, high fecundity rate, no parental involvement, and external fertilization. Males will

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