Lissamphibia

The Lissamphibia (from Greek λισσός (lissós, "smooth") + ἀμφίβια (amphíbia), meaning "smooth amphibians") is a group of tetrapods that includes all modern amphibians. Lissamphibians have three living groups today.

These groups are the Salientia (frogs and their extinct relatives), the Caudata (salamanders and their extinct relatives), and the Gymnophiona (the limbless caecilians and their extinct relatives).

Salientians and caudatans are probably more closely related to each other than to caecilians. The name Batrachia is often used for the group that includes both salientians and caudatans.

There was also a fourth group called the Allocaudata (also known as Albanerpetontidae). This group lived for about 160 million years, from the Middle Jurassic to the Early Pleistocene, but it became extinct two million years ago.

Most scientists think that the main groups of modern amphibians—frogs, salamanders and caecilians—are all closely related. Some people have suggested that an early animal called the Permian dissorophoid Gerobatrachus hottoni might be a lissamphibian. If this is not true, the oldest known lissamphibians are Triadobatrachus and Czatkobatrachus, which lived in the Early Triassic.

Characteristics

Lissamphibians are all the frogs, toads, salamanders, and caecilians alive today. They share some cool features. They often have special joints at the back of their skull. They have two kinds of skin glands: mucous and granular. Many have fat bodies linked to their gonads and a special way to breathe.

Their ribs do not wrap around their bodies, and they can lift their eyes using a special muscle. Their teeth often have two cusps and are separated from the roots by special tissue. Some also have an operculum, a small bone in the skull connected to their shoulder girdle, which may help with hearing and balance.

Relationships and definition

Main article: Labyrinthodontia § Origin of modern amphibians

Lissamphibia is the group that includes all modern amphibians. It has three main groups: frogs, salamanders, and caecilians. Scientists study how these animals are related to each other and to older amphibians. They once thought amphibians came from two different groups of fish, but new discoveries show this is not true.

Today, scientists think Lissamphibia may have come from one of two ancient groups of early four-legged animals. Some believe they evolved by keeping juvenile features into adulthood and becoming very small. Studies of modern amphibians help scientists understand when these groups split apart. Caecilians separated first, followed later by frogs and salamanders. Recent fossil finds also support the idea that all modern amphibians share a common ancestor.