LOCOMOTION IN TRIADOBATRACHUS
has usually been associated with features of a morphofunctional complex formed by the ilia, sacrum, urostyle, and hindlimbs (Emerson and De Jongh 1980; Jenkins and Shubin 1998; Přikryl et al. 2009; Reilly and Jorgensen 2011; Sigurdsen et al. 2012; Jorgensen and Reilly 2013). However, when the morphology of T. massinoti is studied in a phylogenetic context, it appears that elements of this complex did not evolve in a concerted fashion (Fig. 5). This is evident in the early appearance of a frog-like ilium in salientian evolution, as shown by T. massinoti, preceding that of other distinct features of the anuran Bauplan, such as fused zeugopodial bones and urostyle (Fig. 5). This evolutionary decoupling is partially mirrored in the ontogeny of extant frogs, which achieve adult locomotor behavior before the end of metamorphosis, when the limbs are already functional but the sacrum, urostyle, and pelvis are still disarticulated (Fabrezi et al. 2014). In this context, derived postcranial features that T. massinoti shares with frogs, like iliac morphology, would not have originally been linked to a saltatory locomotion and, thus, they might have been co-opted as exaptations in jumping anurans. These interpretations widen the morphological gap between T. massinoti and the earliest frog-like salientians, leaving open questions about the role of locomotion in the origin of the anuran Bauplan.
Acknowledgments We are grateful to A. Báez (Universidad de
Buenos Aires), who kindly provided the high-resolution mold of the holotype of Triadobatrachus massinoti. Thanks are extended to M. Fabrezi (Museo de Ciencias Naturales, Salta) and J. Faivovich (Museo Argentino de Ciencias Naturales) for access to materials under their care. Thanks to P. Milla Carmona (Universidad de Buenos Aires) for his help with the statistical data analyses. This work was supported by grants from AgenciaNacional de Promoción Científica y Tecnológica, and the Universidad de Buenos Aires (UBACyT). A.I.L. is a postgraduate fellow of Consejo Nacional de Investigaciones Cientificas y
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Tecnológicas (CONICET). R.O.G. and I.M.S. are members of Carrera del Investigador Científico (CONICET).
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