Heiss E, Lemell P. 2023. 
In: Bels, V.L., Russell, A.P. (eds) Convergent Evolution. Fascinating Life Sciences. Springer, Cham. doi.org/10.1007/978-3-031-11441-0_6 . Link. Published 27 February 2023

Abstract

Modern amphibians are referred to as Lissamphibia and comprise the three extant groups: Anura (frogs and toads), Caudata (salamanders and newts) and Gymnophiona (caecilians). From a phylogenetic point of view, lissamphibians are considered the sister taxon of extant amniotes (sauropsids and mammals). Lissamphibians have a long evolutionary history, reaching back into the Late Paleozoic and most probably originated within a temnospondyl clade. One of the most conspicuous features of lissamphibians is their aquatic larval stage. Many lissamphibians have, however, secondarily reduced the free-living larval stage and are direct developers. Direct development is a secondary feature and might be seen as an adaptation to terrestrial life. Given that the aquatic larval stage is the ancestral condition for lissamphibians, adaptations to aquatic feeding might also be seen to be the ancestral condition, at least for lissamphibian larvae. After metamorphosis, some lissamphibians become terrestrial, others adopt a semiterrestrial/semiaquatic lifestyle, while others remain fully aquatic. Accordingly, although in many lissamphibian cases the secondary nature of aquatic adaptations might be obvious, a strict distinction between secondary and primary adaptations is less clear in others. Examples of secondarily aquatic lissamphibians are aquatic frogs and toads, as well as some desmognathid salamanders that have definitely reinvaded aquatic trophic habitats during their evolutionary history. In contrast, some salamandrid and ambystomatid salamanders continuously switch between aquatic and terrestrial lifestyles after metamorphosis and it is not obvious whether their (semi)aquatic lifestyle is retained from their larval condition (i.e. primary) or has evolved de novo. In fact, many adaptations to aquatic feeding in lissamphibians might represent a combination of both primary and secondary features, defying a strict dichotomy. In this chapter we summarize aquatic feeding strategies in all three extant groups of lissamphibians and highlight homologous and convergent features where appropriate.