Urodeles

Urodeles, also referred to as urodela or caudata in some classifications, are an order of amphibians that includes the salamanders and newts. They are characterized by an elongated body, four limbs of roughly equal size, a distinct tail, and moist, smooth skin. Most species have aquatic or semi-aquatic larval stages with gills, while many adults are terrestrial or semi-aquatic and rely on a combination of respiration through the skin and lungs or gills.

Reproduction in urodeles is typically sexual, with internal fertilization achieved by a male depositing a spermatophore that the female collects. Eggs are laid in water or in damp habitats, and larvae generally resemble miniature adults but possess gills and are usually aquatic. Metamorphosis occurs in many species, though some exhibit direct development on land. A number of urodeles display paedomorphosis, retaining larval traits such as gills into adulthood, as seen in species like the axolotl.

Urodeles are distributed primarily across the temperate northern hemisphere, with a diversity peak in North America and Eurasia. They inhabit a range of habitats, from forests and grasslands to streams, ponds, and subterranean environments. Ecologically, they are largely carnivorous, feeding on invertebrates and other small prey, and they occupy various niches from fully terrestrial to fully aquatic lifestyles.

Taxonomy varies among sources, but urodeles are commonly treated as equivalent to the order Caudata. Families often cited include Cryptobranchidae (giant salamanders), Hynobiidae (Asian salamanders), Salamandridae (true salamanders and newts), Ambystomatidae (mole salamanders), Plethodontidae (lungless salamanders), Proteidae, Sirenidae, and Amphiumidae. The group comprises roughly several hundred described species, reflecting substantial diversity and ecological variety.

Conservation concerns are notable: many species are threatened by habitat loss, pollution, climate change, invasive species, and emerging diseases such as chytridiomycosis and Batrachochytrium salamandrivorans.