Cannibalism in a small growth stage of the Early Permian branchiosaurid Apateon gracilis (Credner, 1881) from Saxony

Cannibalism has been observed in a variety of extant amphibians. In some species, cannibalism is a common phenomenon, whereas in others, it is an optional behaviour (Warburg et al. 1979; Crump et al. 1992; Degani 1993; Bressi et al. 1996; Thiesmeier 2004). Most frequently, amphibian eggs and larvae are subjected to cannibalistic predation, and most cannibals are found among larvae of urodelans and anurans. Superficially similar to extant urodelan larvae are the branchiosaurids, a group of temnospondyl amphibians that are known from Late Carboniferous to Permo-Triassic strata and reached an adult body size of 150 mm. Branchiosaurids exhibit larval characters such as branchial dentition and external gills, and most of them are considered to be paedomorphic, water-dwelling animals (Bystrow 1939; Boy 1972; Boy & Sues 2000). Their branchial denticles, attached to the mostly cartilaginous ceratobranchials, are often split distally into several tips and formed a fine trap in the gill region, suggesting that branchiosaurids relied on filter feeding of phytoand zooplankton at least to some extent (Boy 1993; Boy & Sues 2000). However, large growth stages of branchiosaurids also fed on small vertebrates such as other branchiosaurid species or small fishes. Werneburg (1988a) reported large specimens of Melanerpeton eisfeldi (Werneburg, 1988) from Early Permian strata of the Thuringian Forest that preyed on small growth stages of Apateon kontheri (Werneburg, 1988), as indicated by gut contents. Rare cases of cannibalism have been reported in which small conspecifics have been discovered in the digestive tract of large branchiosaurids (Werneburg 1989). In the present study, I describe a small growth stage of the branchiosaurid Apateon gracilis from the Early Permian D hlen Basin in Saxony with a smaller, nearly complete conspecific preserved in its digestive tract. Werneburg (1991) revised Apateon gracilis and referred it to Melanerpeton gracile. A recent comprehensive phylogenetic analysis of branchiosaurids by Schoch & Milner (2008), however, suggests the assignment of this species to the genus Apateon (see also a discussion of characters in Schoch & Fr bisch 2006). Therefore, the binomen Apateon gracilis is preferred in the present study. Apateon gracilis is a medium-sized branchiosaurid that is represented by different growth stages ranging from 6 to 23 mm skull length, and is the only branchiosaurid species known so far of which metamorphosed, land-dwelling stages have been found (Werneburg 1991; Schoch & Fr bisch 2006). Apart from Niederh slich in the D hlen Basin, Apateon gracilis has been demonstrated in the southwestern Saale Basin in Thuringia (Werneburg 1988b, 1991). The Niederh slich de-