A new Early Carboniferous tetrapod with a mélange of crown-group characters

Abstract

Living (that is, crown-group) tetrapods represent the phylogenetic end-points of two lineages which diverged from each other during the mid/late Palaeozoic era. These two groups of tetrapods are the Amphibia (frogs, salamanders and caecilians), with their roots among temnospondyls1,2, and the Amniota (mammals, turtles, crocodiles, birds, lizards and snakes), with their roots among anthracosaurs3,4. The earliest representatives of both lineages, including a stem amniote, are known from the Visean of East Kirkton, Scotland5. Here I describe a new taxon from this locality that not only combines characters of each lineage, but also represents the basal member of a third Palaeozoic group, the baphetids. The baphetids lie within the base of the crown clade of tetrapods and the morphology of the new taxon, their most primitive member, is a new benchmark for studying the polarity and evolution of crown tetrapod characters.