No abstract

Sesamoids are skeletal elements rarely considered in studies of the vertebrate skeleton. In this work, we integrate ontogenetic data of anuran sesamoids in two species (Leptodactylus latinasus and Pleurodema cf. guayapae), the related structures (tendons, muscles, and joints) in L. latinasus, and a survey of sesamoid distribution in 185 anuran taxa. Our main goals are: (1) to contribute to the knowledge of the comparative anatomy of sesamoids in tetrapods; (2) to provide additional developmental evidence to interpret the ontogenetic pattern of sesamoids in anurans, as a key to elucidate that of tetrapods in general; (3) to provide data about tendon development in relation to sesamoid development in anurans for the first time; and (4) to propose a pattern of anuran sesamoid distribution. The homologies of sesamoids across tetrapods are discussed here. Observations were made in cleared and stained skeletal whole-mounts. Fifty-four sesamoids were found in anurans, thirty-seven of which occur in L. latinasus. The traditional point of view of embedded sesamoids always resulting from biomechanical stimuli of a previously existing tendon is not sustained by our data. Many sesamoids arise before the differentiation of a tendinous tissue. Our survey results in a data set where the two big anuran clades, Hyloides (12 families) and Ranoides (14 families), were represented. The matrix has 38% missing entries. Most of the surveyed sesamoids have multiple origins, with only three of them (about 19%) having one origin. Anat Rec, 293:1646Rec, 293: -1668

The genus Leptodactylus is predominantly Neotropical (a few species have colonized the southern Neartic region) and is distributed from Texas to Argentina and on certain Caribbean islands. Leptodactylus was divided into five groups of species: Leptodactylus melanonotus, Leptodactylus ocellatus, Leptodactylus fuscus, Leptodactylus pentadactylus and Leptodactylus marmoratus. Among these, the L. fuscus group is the one with most species, with 27 taxa. Characters unverified in most of the species are used to define the L. fuscus group. However, the monophyly of the group has never been tested rigorously in a quantitative phylogenetic context. Thus, the main goal of this study was to test such monophyly and to construct a phylogeny of the L. fuscus group. A matrix of 114 characters scored across 43 taxa was constructed, with 31 characters taken from external morphology, 58 from adult skeletons, 16 from larval chondrocranium, 5 from ethology and 4 from morphometric data were included. Out of all the species examined, 23 belonged to the ingroup and 20 to the outgroup. The data set was analysed with implied weights, by using TNT software. The monophyly of the group was strongly supported in the fittest cladogram obtained. The optimizations of some characters on this hypothesis support traditional evolutionary hypotheses. The optimizations also suggest the presence of paedomorphic character states in some species, which is also discussed.

We present the ontogeny of the integrated musculoskeletal complex that comprises the pelvic girdle and hind limbs of anurans. Our histological data show that the pelvic girdle originates from a single mesenchymatic condensation. The tissue differentiation sequence is cartilage, muscle and tendon. The intrusion of the ischiadic nerve into the limb bud is produced very early in ontogeny. The pre‐cartilage appears in the pre‐motile stage. Therefore, the nerve produces a movement analogous to the ‘embryonic motility’ that would induce the emergence of the pre‐cartilage. The acetabulum is the first of all cavitation processes to form, the second one being the knee. The acetabulum appears before the muscles are mature, although it has been stressed that the muscle contraction maintains joint progenitors committed to their fate. Our data indicate an explosive differentiation of all 11 muscular masses together. We provide three new characters that support the monophyly of Hyloides, Acosmanura and Neobatrachia.