ORIGINAL PAPER Functional Indices and Postnatal Ontogeny of Long Bones of the Forelimb in the Sigmodontine Rodents (Rodentia: Cricetidae) Luz Valeria Carrizo 1 & María José Tulli 2 & Virginia Abdala 3 # Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract The adaptations for a particular locomotor type (e.g., fossorial or saltatorial) could affect limb bone morphology throughout ontogeny. We explore how the measurements of the forelimbs and functional indices change along the postnatal ontogeny of 92 specimens of sigmodontines belonging to four genera (Akodon, Eligmodontia, Oligoryzomys, and Oxymycterus) with different locomotor types (ambulatory, quadrupedal-saltatorial, scansorial, and semifossorial). We examined individuals of different age categories: juveniles, young adults, and adults. Eleven linear measurements of long bones (humerus, radius, and ulna) corre- sponding to functional diameters and lengths were taken and analyzed through simple regressions (RMA) using geometric mean transformations. Six morphofunctional indices were then calculated and analyzed through multivariate analysis (MANOVA). The allometric patterns and morphofunctional indices show that the forelimb tends to be elongated and slender in the ambulatory, scansorial, and quadrupedal-saltatorial species, and short and thicker in the semifossorial species. Morphofunctional indices do not separate our sample concerning age categories, possibly indicating that the juveniles of different rodent species are born with similar morphology to the adults in terms of locomotion. Keywords Bone growth . Ecomorphology . Locomotor type . Sigmodontinae Introduction The limbs of mammals exhibit a variety of forms that reflect the diversity of their habitats and their functional capability (Hamrick 2003; Polly 2007). Morphological specialization for a particular locomotor behavior (e.g., fossorial or saltatorial) could affect the appendicular skeletal morphology throughout ontogeny (Lammers and German 2002; Hamrick 2003). Most studies in Mammalia and Tetrapoda that examine the scaling and allometry of long bone proportions have focused on interspecific compar- isons among adults, and few studies have investigated the allom- etry of limb bone proportions during ontogeny (e.g., Biewener 1983; Carrier 1983; Bou et al. 1987; Christiansen 1999; Lammers and German 2002; Schilling and Petroviitch 2006; Kilbourne and Makovicky 2012). Carrier (1983) analyzed the allometric changes in the musculoskeletal system in the black- tailed jackrabbit Lepus californicus. He found that the long bones increase their gracility during ontogeny and suggested that this allometric change would allow enhancement in the performance of juveniles. Lammers and German (2002) found that limb bone length proportions differed among four species studied and between neonates and adults. Within each species, neonates showed proximal and middle elements proportionally shorter than adults, whereas distal elements were proportionally shorter in adults. Recently, Kilbourne and Makovicky (2012) studied how the long bone allometry varied across several mammalian taxa concerning both taxonomy and body size and concluded that the allometric pattern defining mammalian growth is Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10914-020-09512-x) contains supplementary material, which is available to authorized users. * Luz Valeria Carrizo luzvaleria.carrizo@gmail.com * María José Tulli majotulli@gmail.com 1 Laboratorio de Genética Evolutiva, UNaM-CONICET, Instituto de Biología Subtropical (IBS)-nodo Posadas, Félix de Azara 1552, CPA, N3300LQF Posadas, Argentina 2 Unidad Ejecutora Lillo-CONICET, Instituto de Herpetología-Fundación Miguel Lillo, Miguel Lillo 251, 4000 Tucumán, Argentina 3 Cátedra de Biología General, Facultad de Ciencias Naturales, UNT, Instituto de Biodiversidad Neotropical (IBN), UNT-CONICET, Horco Molle S/N, 4107, Yerba Buena, Tucumán, Argentina Journal of Mammalian Evolution https://doi.org/10.1007/s10914-020-09512-x