One frog's tadpole grows to 27 centimetres, then shrinks as it matures
The paradoxical frog earns its name. Its tadpoles can stretch to 27 centimetres, longer than any other frog larva, yet the adult that emerges measures only a few centimetres from snout to vent. Metamorphosis rebuilds almost everything about a tadpole, from its breathing to its gut, so shrinking is less strange than it sounds.
A tadpole is the larval stage of an amphibian, sitting between embryo and adult. The word comes from Middle English taddepol, literally toad-head, and the folksy polliwog shares the same head element joined to a word meaning to wiggle. Most tadpoles live in water and carry fish-like gear the adults lack: gills, a swimming tail and a lateral line for sensing movement. Frog tadpoles start with external gills that skin later covers, venting water through openings called spiracles, and hatchlings use a cement gland to stick to objects.
Most frog tadpoles graze on soft, decaying plants, digesting them in a long coiled gut often visible through the belly. Some break the pattern. Tadpoles in the family Ceratophryidae are gaping-mouthed carnivores that eat other tadpoles, and New Mexico spadefoot tadpoles can switch to a meat diet when food runs short, growing broader heads and stronger jaws. Others filter plankton or skim the surface with funnel-shaped mouths. Salamander and caecilian larvae are carnivorous from the start.
During metamorphosis the hind legs appear first, then the front ones, lungs develop and the tadpole begins gulping air at the surface. The tail is absorbed through programmed cell death, the mouth widens to the full breadth of the head, and the intestine shortens for an adult diet of animals. Some species skip the free-swimming stage entirely and hatch as miniature froglets.
Parental care can be elaborate. Female Pipa frogs carry eggs embedded in the skin of their backs, male midwife toads wrap eggs around their legs, poison dart frogs ferry tadpoles to small pools, and some mothers lay unfertilised eggs as tadpole food. Soft bodies rarely fossilise, but bacterial films preserved tadpoles in Miocene rock, and the oldest clear fossil, from the Middle Jurassic, was described in 2024. Ancient Egyptians used a tadpole hieroglyph to write 100,000.
Source: Tadpole
