Lissamphibia

The Lissamphibia (from Greek λισσός (lissós, "smooth") + ἀμφίβια (amphíbia), meaning "smooth amphibians") is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: 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 likely more closely related to each other than to caecilians. The name Batrachia is commonly used for the clade combining salientians and caudatans. A fourth group, the Allocaudata (also known as Albanerpetontidae) is also known, spanning 160 million years from the Middle Jurassic to the Early Pleistocene, but became extinct two million years ago.

Most scientists have concluded that all of the primary groups of modern amphibians—frogs, salamanders and caecilians—are closely related. Some writers have argued that the early Permian dissorophoid Gerobatrachus hottoni is a lissamphibian. If it is not, the earliest known lissamphibians are Triadobatrachus and Czatkobatrachus from the Early Triassic.

Characteristics

Lissamphibians, which include all modern amphibians, share several interesting features. They often have double or paired occipital condyles, which are special joints at the back of the skull. They also have two types of skin glands: mucous and granular. Many have fat bodies linked to their gonads and a special way to breathe using a forced-pump mechanism.

Additionally, 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 a 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 have studied how these animals are related to each other and to older amphibians. They used to think amphibians came from two different groups of fish, but new discoveries show this is not true.

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