Frog locomotion has attracted wide scientific interest because of the unusual and derived morphology of the frog pelvic girdle and hind limb. Previous authors have suggested that the design of the frog locomotor system evolved towards a specialized jumping morphology early in the radiation of the group. However, data on locomotion in frogs are biased towards a few groups and most of the ecological and functional diversity remains unexplored. Here, we examine the kinematics of swimming in eight species of frog with different ecologies. We use cineradiography to quantify movements of skeletal elements from the entire appendicular skeleton. Our results show that species with different ecologies do differ in the kinematics of swimming, with the speed of limb extension and especially the kinematics of the midfoot being different. Our results moreover suggest that this is not a phylogenetic effect because species from different clades with similar ecologies converge on the same swimming kinematics. We conclude that it is important to analyze frog locomotion in a broader ecological and evolutionary context if one is to understand the evolutionary origins of this behavior. KEY WORDS: Anura, Kinematics, Locomotion, Swimming INTRODUCTIONFrog locomotion has attracted wide scientific interest because of the unusual and highly derived morphology of these animals (Barclay, 1946; Estes and Reig, 1973;Zug, 1978; Frost et al., 2006). Frogs are characterized by a shortened trunk and tail, elongated ilia and elongated hind limbs. This morphology has been interpreted as being associated with a jumping life style and thus it has been suggested that jumping evolved early in the evolution of the lineage (Gans and Parsons, 1966;Shubin and Jenkins, 1995; Jenkins and Shubin, 1998) and many recent studies have attempted to infer locomotion in basal frogs (Prikryl et al., 2009; Essner et al., 2010;Reilly and Jorgensen, 2011;Sigurdsen et al., 2012;Venczel and Szentesi, 2012; Jorgensen and Reilly, 2013). However, kinematic and electromyographic studies indicate strong similarities between the mechanics of swimming and jumping in some frogs (Emerson and De Jongh, 1980;Peters et al., 1996; but see Nauwelaerts and Aerts, 2003), implying that morphological features associated with these two locomotor modes may not be that different. This may, in turn, complicate inferences of locomotor modes from anatomy as is often done for extinct animals. Despite their rather uniform morphology, frogs are an ecologically diverse and speciose group with over 5000 known species (Frost et al., 2006). Moreover, animals with different ecologies have evolved different morphologies and show different levels of locomotor performance (Moen et al., 2013), suggesting that locomotion differs in animals with different ecologies. RESEARCH ARTICLETo date, most of our knowledge on frog locomotion is based on data for a limited set of derived frogs including ranoids [mostly ranids and bufonids (Calow and Alexander, 1973; Lutz and Rome, 1994;Kamel et al., 1996;Pet...

The ontogenetic development of the pectoral girdle in seven anuran species (Xenopus laevis, Discoglossus pictus, Bombina bombina, Bombina variegata, Pelobates fuscus, Bufo bufo and Rana dalmatina) was studied using cleared and stained specimens. The epicoracoid cartilage was found to develop in two different ways resulting in an arciferal or firmisternal type of the pectoral girdle. In the arciferal one, the epicoracoid originates from a medial prolongation of the procoracoid cartilage and broadly overlaps its counter part during further development. In the firmisternal pectoral girdle, the epicoracoids are formed by the widened cartilaginous medial edges of the coracoids that fuse together along the midline. Polarization of ontogenetic characters shows, that omosternum evolves inside Anura, and the type of sternum occurring in basal Anura seems to be an apomorphy of all Batrachia. The sternal elements have a single or paired rudiment, their development is connected with M. rectus abdominis or a zonal area and they remain cartilaginous or ossify during postmetamorphic development. An occurrence of omosternum in Barbourula busuangensis was described for the first time.