Which Triassic amphibian is often described as an early stem-frog?

The Triassic amphibian often described as an early stem-frog is Triadobatrachus.

The genus is known from Triadobatrachus massinoti, which lived during the Early Triassic about 250 million years ago in what is now Madagascar. It is generally regarded as the oldest known member of the frog lineage and as a transitional fossil between more primitive amphibians and later frogs.

Triadobatrachus already had several frog-like features, including a skull shaped broadly like that of a frog and elongated hind limbs. However, it was not a modern frog. It retained at least 26 vertebrae, including a short tail, whereas living frogs typically have only four to nine vertebrae and no adult tail. Its anatomy also suggests that it probably could not perform the powerful jumping locomotion characteristic of modern frogs.

The name can be confused with Czatkobatrachus, another Early Triassic stem-frog from Poland. That related animal is also discussed in accounts of early frog evolution, but Triadobatrachus is the much more familiar answer in general-audience quizzes. The later Early Jurassic Prosalirus is closer to modern frog anatomy and is often cited as an early jumping frog.