Animals

Caudates - Salamanders and Newts

Caudates are members of the order Caudata, the order of amphibians that comprises the salamanders and newts. This order is sometimes called Urodela.

Caudates can be found on every continent on Earth except for Australia and Antarctica. Most species live in temperate zones in the northern hemisphere. Some live in the tropics.

Difference Between Newts and Salamanders

A newt is a type of salamander. All newts are salamanders, but not all salamanders are newts.

Fire salamanderWithin the order Caudata, there is a family known as Salamandridae. Members of the family Salamandridae are divided between two groups, the true salamanders and the newts.

The term "newt" is sometimes to refer to any salamander (caudate) that lives on land as an adult, and returns to water only to breed.

Newts tend to have rough, warty skin while salamanders that have smooth skin.

Reproduction

In some caudate species, the female lays eggs and the male fertilizes the eggs when they are outside the female's body. This process is known as external fertilization.

The female lays eggs in a moist place, such as in a pond or on moist soil.

Other species of Caudata reproduce by means of internal fertilization. When the eggs are still inside the female's body, the male deposits his sperm inside her body.

In some species that practice internal fertilization, the female keeps the fertilized eggs inside her body until they hatch. The young are born live.

Animals that give birth to live young are viviparous, while animals that lay eggs are oviparous.

Sometimes, species in which the female gives birth to live young, but does not have a placenta, as in placental mammals, are said to be ovoviviparous. In ovoviviparous animals, the young are nourished by an egg yolk, rather than by a placenta.

Those salamanders that bear live young are ovoviviparous.

Both males and female caudates have cloacas. A cloaca is an opening that is used for both excretion and reproduction. Male caudates release sperm through their cloacas and females lay eggs through their cloacas.

In those salamanders that practice internal fertilization, the male's sperm enters the female's body through her cloaca.

Female salamanders that give birth to live young give birth through their cloacas.

Life Cycle

Caudate larvae live in water. They breathe through gills.

The larvae are carnivores. Their diet mainly consists of arthropods.

They usually look like small fish. Sometimes, salamander larvae will have legs.

A larva transforms into an adult during metamorphosis.

If the larva has no legs, it will grow legs. If it already has legs, the legs grow longer.

Often, a larva will lose its gills and grow lungs.

Some species of salamander retain their gills as adults.

Some salamanders have neither gills nor lungs when they are adults, and breathe only through their skins.

Unlike frogs and toads, which lose their tails after metamorphosis, salamanders keep their tails when they are adults.

Some salamanders do not go through metamorphosis. They look like larvae throughout their lives. These salamanders are known as neotenic salamanders. Neoteny is the condition in which an adult animal retains the traits of a juvenile.

Other salamanders look like miniature adults from the moment they hatch.

Eastern newt of North America in the eft stage

Newt Life Cycle

Newts go through three life stages.

The first stage is the larval stage.

After a newt larva goes through metamorphosis, it arrives at its second life stage, when it is known as an eft.

Efts live on land. They have no gills. They have legs and lungs.

The final life stage is the adult stage.

Some newts return to the water when they become adults, while others remain on land and return to the water only to breed.

Physical Characteristics of Adult Caudates

Adult caudates often resemble lizards.

They have slim bodies and long tails.

Salamanders usually have four short legs, all of which are all the same size.

They have four toes on their front feet and five toes on their hind feet.

Some species, particularly those that live in water or burrow underground, may have legs that are extremely small, have no back legs or have or no legs at all.

Some salamanders have webbed feet.

Salamanders have narrow heads and small eyes.

They have teeth in both their upper and lower jaws.

Adult caudates are usually between about 4 and 6 inches long.

The smallest caudates are about 1 inch long. They belong to a group of salamanders known as minute salamanders.

The largest salamander in the world is the Chinese giant salamander. It can reach a length of almost 6 feet long and weigh as much as 140 pounds. The Chinese giant salamander is the largest amphibian on Earth.

Respiration

Salamander larvae live in water and breathe through gills.

Some caudate species lose their gills during metamorphosis and breathe through simple lungs when they are adults.

There are salamanders that live in water when they are adults, yet use lungs to breathe.

Some species never lose their gills. They continue to breathe through gills when they are adults.

Still other salamanders keep their gills and grow lungs as well. As adults, they use both gills and lungs to breathe.

All salamanders breathe through their skins, through a process known as cutaneous respiration.

Some species lose their gills during metamorphosis but never grow lungs.

These salamanders breathe only through their skins.

All caudates must keep their skins moist so that gases can pass in and out.

Salamanders have glands on their skin that produce mucus. The mucus helps to keep the skin moist.

Behavior

Some adult salamanders live in water. Others live on land.

Arboreal salamanders climb trees.

To keep their skins moist, salamanders stay in moist places, such as on the bottoms of ponds or streams, on moist soil or under rocks or logs.

Caudates defend themselves against predators by secreting toxins from their skin.

Salamanders are often brightly colored. Once a predator bites a salamander and ingests some of its toxin, the predator learns to avoid salamanders with the same coloration.

Adult caudates are carnivorous and, like larvae, eat mostly arthropods.

Salamanders don't like direct light. They are often nocturnal (active at night).

Some caudate species estivate in hot or dry environments. Some hibernate when it becomes very cold.

Estivation and hibernation are states in which an animal's metabolism is markedly reduced.

The destruction of wetland habitats has caused a decline in the populations of many caudate species

Regeneration

If a salamander loses its tail or any of its limbs, it can regenerate it (grow it back).

Caudates can also regenerate parts of their eyes, parts of their hearts, parts of their spinal cords and parts of their brains.

Scientists are researching how salamanders regenerate. They hope to use the knowledge they gain to help people regenerate lost body parts and to prevent human cells from becoming cancerous.