Lizard-shaped amphibians that can regrow whole limbs
Salamanders look lizard-like with slender bodies, blunt snouts, and right-angled limbs, yet they are amphibians. Diversity peaks in eastern North America, especially Appalachia, mostly across the Holarctic. Researchers study their regeneration of lost limbs and other tissues for medical clues.
All ten living salamander families belong to the order Urodela. The English name comes via French and Latin from a Greek word for the fire salamander, possibly borrowed from an older pre-Greek language. They range from minute salamanders just 27 millimetres long, tail included, to the Chinese giant salamander, which can reach 1.8 metres and 65 kilograms; the largest kinds, giant salamanders, sirens, Congo eels and proteids, are all aquatic. Front feet carry at most four toes and hind feet five, though some species have fewer, and sirens and amphiumas have lost or shrunk their hind legs, giving them an eel-like look.
Except in newts, vertical costal grooves run down the flanks. The scaleless skin is thin, breathes, and is kept moist by mucus that also wards off bacteria and makes the animal slippery to grab; granular glands on the head, back and tail secrete distasteful substances. It is shed periodically under pituitary and thyroid control, splitting first around the mouth. Some newts carry tetrodotoxin and advertise it with bright colours, and male newts turn vivid when breeding.
Most have eyes tuned to night vision, though in cave species like the Georgia blind salamander they are missing or skinned over. Salamanders see in three colours reaching into the ultraviolet, with receptors peaking around 450, 500 and 570 nanometres, and larvae and fully aquatic adults feel water pressure through a fishlike lateral line. With no eardrum or middle ear, they pick up sound through a bone-and-muscle link to the shoulder girdle. Largely silent, some tick, click or squeak, perhaps with nasal valves, and females may release chemicals to lure males.
The Appalachian Mountains hold more species than anywhere else, and while most salamanders are Holarctic, a few range into the Neotropics. Their ability to regrow limbs and other damaged tissues attracts medical researchers hoping to treat brain and spinal injuries or limit scarring after heart surgery.
Source: Salamander
