It has been hypothesized that morphological diversity within clades can be generated by simple alterations of shared developmental programs. However, few studies have examined changes in heterochrony, the rate and timing of developmentalevents, in an explicitly phylogenetic context. We studied how developmental patterns have changed phylogenetically in the northern swordtail clade of Xiphophorus. We reared individuals of an outgroup and seven of nine species in the clade and followed their development for ~ 300 days. For each individual, we used nonlinear regression toestimatethreegrowth parameters:growth rate,adultbody size,and ageofcessation of growth. Weestimated sword growth rates in males by linear regression. We then used the means of these growth parameters toconstructstandard growth curves for each species and tostudy growth patterns in a phylogenetic context. A combined phylogeny was constructed from both phenotypic and DNAsequencedata.Thephenotypicdataset,compiled fromtheliterature,consistedof86 mor- phological, pigmentation, behavioral, and random amplieed polymorphic DNA characters, many of which had not been used before for phylogenetic analysis. DNA sequence data from three genes for a total of 1284 bases were also obtained from the literature and included in the analysis. Rela- tionships between growth parameters were examined by phylogenetically independent contrasts in relation to seven different phylogenies based on the most-parsimonious trees generated from the phenotypic, DNA sequence, and combined data sets; this allowed us to identify relationships between variables that were not sensitive to ambiguities in Xiphophorus phylogeny. Our analysis revealed statistically signiecant correlations between female body size and male body size, and between femalegrowth rateand malesword growth rate, for allseven phylogenies. Marginally sta- tistically signiecantrelationships werealsoidentieed between female body sizeand femalegrowth rate, and between female growth rate and male body size. We relate these relationships to what is known about the ecology, genetics, and behavior of Xiphophorus to better understand the evolution of growth patterns of both the body as a whole and the sword in particular. The relationship of thesedata totheevolution of swords is discussed. (Development; evolution; growth; heterochrony; independent contrasts; sword; Xiphophorus.) Heterochrony, or changes in the timing of developmental events, has been shown to be a pervasive force in the evolution of mor- phology. Changes in onset, offset, and the rate of development of morphological char- acters have been the basis for much of the observed morphological variation among many types of organisms (Gould, 1977; Al- berchetal.,1979;McKinneyandMcNamara, 1991). However, only when heterochronic changesareexaminedinaphylogeneticcon- text can the evolutionary patterns and pro- cesses of heterochrony be understood (Fink, 1982). The esh genus Xiphophorus (Poeciliidae), comprising 22 described species of sword-