ORDER: Caudata
--
Salamanders,
newts & sirens
Definition:
Lizard-like
amphibians
with at least one pair of limbs at some time in their life cycle, and
a post-cloacal tail in both larval and adult stages. There is a
distinct, if short, neck in adults. Fore and hind limbs are about equal in
length. Restricted to the Northern Hemisphere, with the greatest
species diversity seen in the Appalachian Mountains of the United
States.
One family of terrestrial salamanders, the Plethodontidae, lacks lungs
and conducts all respiration cutaneously. Many salamanders use
internal fertilization and lay eggs on land, in humid recesses under
boards or rotting logs.
Overview: The
salamanders show relatively little morphological variation for the
different habitats they occupy. In salamanders, generally, the larval
and adult forms differ less markedly than in other amphibians, and
many adults retain juvenile characteristics (neoteny). In particular,
this neoteny can be observed in the families Cryptobranchidae (which
looses external gills but retains a respiratory spiracle), Amphiumidae
(reduction of limbs, no eyelids, retention of gills), Sirenidae
(remains almost totally larval), and Proteidae (retains external
gills, loss of eyes). All of these families represent species that
remain aquatic as adults and, despite retention of larval
characteristics, are reproductively viable.
Other aquatic
forms, which grow beyond their juvenile traits, are noted for
streamlined bodies, developed fingers and toes (=digits), and
possession of a caudal (=tail) fin. The tail is laterally compressed
(i.e., in Ambystoma, Taricha, and Triturus),
though it may eventually loose a good deal of its compression in
certain forms that undergo a period of time as land-dwelling animals
(i.e. Notophthalmus). Aquatic species that live in swift-moving
water (Necturus, Cryptobranchus), however, may have
strong limbs and digits. Unusual, pale and eyeless cave-dwelling
salamanders tend to be aquatic species (i.e., Gyrinophilus, Proteus,
and Typhlomolge).
Fossorial
(=burrowing) species tend to have long cylindrical bodies and tails,
reduced limbs, and a short broad head. Such species often loose the
bright colors seen in many other salamanders, but the exceptions tend
to be brilliantly colored. Some fossorial salamanders, such as Ambystoma
and Salamandra have stout, well-developed limbs.
Among
salamanders, fertilization typically involves the deposit of a sperm
plug by the male, which is picked up by the cloaca of the female,
allowing internal fertilization. The only salamanders known that
practice true external fertilization (male "silts" laid eggs
with sperm) are in the families Cryptobranchidae, Sirenidae, and
Hynobiidae.
