Frogs and toads develop from tadpoles that emerge from the egg. Right? Not necessarily. They don't all do this.
Hundreds of species go straight from egg to frog. True, they hatch as a small frog that grows into a big frog. But it's a frog, without an aquatic stage of metamorphosis.
The squeaking frog Pristimantis of Africa is one such. The Pipa she-toad broods her eggs on her back (don't ask how the eggs get there), from where the babies emerge as tiny Pipa toads. The South American flea toad, which is the smallest-known vertebrate and could fit its whole family on your fingernail, also skips the tadpole stage.
(While miniaturizing, some flea toad species also eschewed a middle ear, apparently rendering them deaf to their own mating calls, which is sad.) In short, the anurans are a vastly diverse bunch, yet the thinking is that they – frogs and toads – are characterized by a biphasic life cycle: egg to larva (tadpole) to frog. The snag is, frogs and toads arose at least 215 million years ago, and possibly more.
Yet not even one lousy tadpole could be identified in the pre-Cretaceous fossil record, which begged dubiety about the ancestral anuran condition. Did early anurans have a biphasic life cycle, as we assume? Did they too hatch from egg as larvae and metamorphose into adults? We still don't know what the first frogs did, but now paleontologists have thrown back the proven emergence of biphasic life in the frog, reporting on the earliest tadpole discovered to date: No.