What ancient trait, retained by caecilians but lost by modern frogs and salamanders, suggests the common ancestor of Lissamphibia had dermal armor?

Answer

Minute, bony scales embedded within their skin

Caecilians possess minute, bony scales within their skin, which suggests their common Lissamphibia ancestor had some form of dermal component that was subsequently lost by frogs and salamanders.

What ancient trait, retained by caecilians but lost by modern frogs and salamanders, suggests the common ancestor of Lissamphibia had dermal armor?
evolutionamphibianancestrytetrapodCaecilian