Postembryonic skeletal development of the pipid frog Xenopus laevis is described from cleared-and-stained whole-mount specimens and sectioned material representing Nieuwkoop and Faber developmental Stages 46-65, plus postmetamorphic individuals up to 6 months old. An assessment of variation of skeletogenesis within a single population of larvae and comparison with earlier studies revealed that the timing, but not the sequence, of skeletal development in X. laevis is more variable than previously reported and poorly correlated with the development of external morphology. Examination of chondrocranial development indicates that the rostral cartilages of X. laevis are homologous with the suprarostral cartilages of non-pipoid anurans, and suggests that the peculiar chondrocranium of this taxon is derived from a more generalized pattern typical of non-pipoid frogs. Derived features of skeletal development not previously reported for X. laevis include 1) bipartite formation of the palatoquadrate; 2) precocious formation of the adult mandible; 3) origin of the angulosplenial from two centers of ossification; 4) complete erosion of the orbital cartilage during the later stages of metamorphosis; 5) development of the sphenethmoid as a membrane, rather than an endochondral bone; and 6) a pattern of timing of ossification that more closely coincides with that of the pelobatid frog Spea than that recorded for neobatrachian species.

Based on a molecular phylogeny, a new phylogenetic taxonomy that is compatible with both the International Code of Zoological Nomenclature (ICZN) and the PhyloCode is proposed for Glassfrogs and their sister taxon, Allophryne ruthveni. The arrangement presented herein emphasizes the recognition of clades having (i) significant statistical support and congruence among phylogenetic estimation methods (i.e., parsimony, maximum likelihood, and Bayesian inference criteria), (ii) congruence among genetic markers, and (iii) morphological and/or behavioral distinctiveness. Also, when previously recognized groups are recovered as monophyletic or nearly monophyletic, we propose taxa that minimize the number of name changes required to make these groups monophyletic, preserving the names and contents of previous classifications (i.e., nomenclatural stability). The evolutionary proximity of Centrolenidae and Allophrynidae is recognized by combining these families into an unraked taxon, Allocentroleniae—a proposal that maintains the traditional names and species contents of Centrolenidae and Allophrynidae. We arrange centrolenid diversity in two subfamilies: Centroleninae and Hyalinobatrachinae. Within Centroleninae, the diagnosis and species content of the genera Centrolene, Cochranella, and Nymphargus are modified; Teratohyla is resurrected and modified, and Chimerella, Espadarana, Rulyrana, Sachatamia, and Vitreorana are proposed as new genera. The other subfamily, Hyalinobatrachinae, contains the new genus Celsiella and a modified Hyalinobatrachium that fully corresponds to the former fleischmanni Group. Additionally, the genus Ikakogi is described. Ikakogi could not be assigned with confidence to either subfamily and it is placed as incertae sedis in Centrolenidae. The data at hand suggest that Ikakogi tayrona is a lineage as old as the subfamilies Hyalinobatrachinae and Centroleninae. The revised taxonomy differs markedly from previous arrangements, which were based on phenetics and few morphological characters. Most of the genera defined herein are confined to distinct biogeographic regions, highlighting the importance of geography in the speciation of Glassfrogs. The principal limitation of this proposal is that it is based on an incomplete sampling of taxa (54% of the recognized Glassfrogs). Although diagnoses are based on phenotypic traits, there are several cases (16% of all species) in which the allocation of species is ambiguous because of morphological homoplasy and the lack of molecular data. Finally, in an attempt to facilitate species identification, comparison, and generic placement, we provide photographs for most (~ 96%) of the recognized centrolenid species.

hylids have been derived from several phyletic lines. In each case the individual lines have undergone similar types of modifications in response to similar environmental situations. These frogs, which seemingly represent a reversal in the evolutionary trend in hylids, show several unique morphological characteristics by which they are functionally adapted to specialized modes of existence, first alluded to by Cope (1865:194) in reference to Triprion petasatiis: "It is interesting that an animal living in rocky situations should present such a cranial bony development; this, in connection with its colors, no doubt, aids especially in concealment, and is another instance of the Creator's bountiful care for his humblest creatures." AcknowledgmentsThe completion of this study has been possible largely through the cooperation of museum curators and owners of private collections who have loaned, donated, or provided data for many valuable specimens. For their cooperation, I thank Mr.