The jaw is only 4.5 cm (1.8 in.) long, making Brittagnathus the smallest known Devonian "tetrapod". A phylogenetic analysis places it among Carboniferous stegocephalians, particularly the small whatcheeriidPederpes, rather than the contemporary Devonian stem-tetrapods. This provides support for an origin for Carboniferous-type tetrapods as early as the Devonian.[1]