Appearance
Salamanders are amphibians with a lizard-like appearance, slender bodies, blunt snouts, short limbs, and tails. They belong to the order Urodela, which means “conspicuous tail,” and are primarily found in eastern North America, especially the Appalachian Mountains. Most salamanders have four toes on their front legs and five on their rear legs, though some species have fewer digits or lack hind limbs. Their permeable skin makes them reliant on moist habitats, with some species fully aquatic, others intermittently so, and some entirely terrestrial.
Salamanders can regenerate lost limbs and vital organs, an ability that has attracted research interest for potential medical applications, such as treating brain and spinal cord injuries. The family Salamandridae, known as newts, lacks the costal grooves found in other groups, and some of these species possess tetrodotoxin, a potent poison, often exhibited through bright coloration. Salamanders typically lay eggs in water, and their lifecycles vary significantly, with some reproducing while still in the larval state.
The skin of salamanders is moist and smooth, except for newts in the Salamandridae family, which may have velvety or warty skin. They can be drab or brightly colored with various patterns, and males become more vibrant during breeding season. Cave-dwelling species often appear translucent due to lack of pigmentation.
Diet
Salamanders are flexible predators that eat a wide range of organisms. Large species, like the Japanese giant salamander, consume crabs, fish, and small mammals, while smaller dusky salamanders in the Appalachian Mountains eat worms, flies, beetles, and more. Sometimes, they even eat each other, especially when food is scarce.
Most salamanders have small teeth on their upper and lower jaws, even in their larvae. Adult teeth help grasp prey and are designed to prevent escape. Salamanders also have patches of teeth in their mouths to hold onto food and regularly replace their teeth throughout their lives.
Terrestrial salamanders catch prey with their sticky tongues in under half a second. High-speed videos show species like the tiger salamander positioning themselves, opening their mouths, and shooting their tongues forward to trap prey in mucus. They then retract their tongues and swallow, using throat muscles and eye pressure for assistance.
Lungless salamanders have special methods for feeding, using muscles to shoot their tongues out. Aquatic salamanders grab food with their teeth and use a technique called inertial feeding, moving water in and out of their mouths to tear apart prey.
Sirenids are unique among salamanders because they can eat plants, using beak-like jaws and long intestines to consume algae and soft plants, including lettuce.
Habitat
Salamanders diverged from other amphibians during the mid- to late Permian, resembling modern Cryptobranchoidea. Their lizard-like appearance results from shared primitive traits, but they are more closely related to frogs and toads within Batrachia. The oldest total-group salamander is Triassurus from the Triassic of Kyrgyzstan, while Valdotriton from the Late Jurassic of Spain is a likely candidate for the oldest crown-group salamander.
Salamanders are primarily found in the Holarctic and Neotropical regions, not beyond the Mediterranean Basin or the Arctic tree line. They had a Laurasian distribution until Bolitoglossa moved into South America from Central America around 23 million years ago. Fossil evidence suggests they once lived in the Caribbean Islands and possibly in Australia.
Currently, there are about 760 living salamander species, with one-third in North America, particularly in the Appalachian Mountains. Here, species have adapted to various habitats. The northern slimy salamander can coexist with the southern gray-cheeked salamander in differing conditions. Additionally, Anderson’s salamander can thrive in brackish or salt water.
Behavior
Many salamanders do not vocalize, relying instead on olfactory and tactile cues for mate identification, with pheromones playing a key role. Males may use their snouts to investigate potential mates. In some species, particularly Old World newts, males display visual cues. Most salamanders mate in water, except for some terrestrial species. Their mating varies from courtship between a single pair to group breeding. In the Salamandroidea clade, which includes 90% of species, fertilization is typically internal, with males usually using indirect sperm transfer via spermatophores. Some species, like the Sardinian and Corsican brook salamanders, transfer sperm directly. In contrast, more primitive groups like giant salamanders and Sirenidae have external fertilization, with males releasing sperm onto egg masses.
Salamanders exhibit three types of egg deposition:
- Ambystoma and Taricha spp. spawn numerous small eggs in predator-free ponds.
- Dusky salamanders and Pacific giant salamanders lay smaller batches of medium eggs in flowing water, often guarded by females.
- ropical climbing salamanders and lungless salamanders deposit a few large eggs on land, which are also protected by the mother. Some species, like fire salamanders, are ovoviviparous, keeping eggs inside until they hatch.
In temperate regions, salamanders typically reproduce seasonally and migrate to breeding grounds, with males often arriving first to establish territories. Following reproduction, a fully aquatic larval stage develops, characterized by external gills, a long body, and a flattened tail. Larvae can be pond-type, with balancers and broad fins, or stream-type, which are more slender and may already possess hind limbs. The carnivorous larvae stage can last from days to years, but some species, like lungless salamanders, skip this stage entirely, developing directly into miniature adults.
Metamorphosis in salamanders is quick, involving the loss of gills and tail fins, the development of eyelids, a wider mouth, and teeth as they transition to terrestrial adults. However, not all salamanders undergo this process; neoteny allows some, like the axolotl, to retain juvenile features while achieving reproductive maturity. This condition can occur due to various environmental factors or genetic influences that inhibit the typical metamorphic changes. Neoteny enables these species to survive in harsh terrestrial conditions, even reaching sexual maturity while still in their larval forms.
Biometrics
Salamanders vary in size, from tiny species measuring just 27 mm (1.1 in) to the Chinese giant salamander reaching up to 1.8 m (6 ft) and 65 kg (145 lb). The largest species belong to the aquatic families of giant salamanders, sirens, Congo eels, and Proteidae, while many terrestrial salamanders, like the Pacific giant salamanders, are smaller. Most salamanders range from 10 to 20 cm (4 to 8 in) in length.
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