Paleobiology, 42(4), 2016, pp. 612–623 DOI: 10.1017/pab.2016.11


Walk before you jump: new insights on early frog locomotion from the oldest known salientian


Andrés I. Lires, Ignacio M. Soto and Raúl O. Gómez


Abstract.——Understanding the evolution of a Bauplan starts with discriminating phylogenetic signal from adaptation and the latter from exaptation in the observed biodiversity. Whether traits have predated, accompanied, or followed evolution of particular functions is the basic inference to establish the type of explanations required to determine morphological evolution. To accomplish this, we focus in a particular group of vertebrates, the anurans. Frogs and toads have a unique Bauplan amongvertebrates, with a set of postcranial features that have been considered adaptations to jumping locomotion since their evolutionary origin. This interpretation is frequently stated but rarely tested in scientific literature. We test this assumption reconstructing the locomotor capabilities of the earliest known salientian, Triadobatrachus massinoti. This extinct taxon exhibits a mosaic of features that have traditionally been considered as representing an intermediate stage in the evolution of the anuran Bauplan, some of which were also linked to jumping skills. We considered T. massinoti in an explicit evolutionary framework by means of multivariate analyses and comparative phylogenetic methods. We used length measurements of major limb bones of 188 extant limbed amphibians (frogs and salamanders) and lizards as a morphological proxy of observed locomotor behavior. Our findings show that limb data correlate with locomotion, regardless of phylogenetic relatedness, and indicate that salamander-like lateral undulatory movements were the main mode of locomotion of T. massinoti. These results contrast with recent hypotheses and indicate that derived postcranial features that T. massinoti shared with anurans might have been later co-opted as exaptations in jumping frogs.


Andrés I. and SotoIgnacioM. Lires. IEGEBA (CONICET/UBA)–Departamento de Ecología Genética y Evolu- ción, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160, Buenos Aires C1428EGA, Argentina. E-mail: andreslires@gmail.com, soto@ege.fcen.uba.ar


Raúl O. Gómez. CONICET–Laboratorio de Paleontología Evolutiva de Vertebrados, Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160, Buenos Aires C1428EGA, Argentina. E-mail: raulgomez@gl.fcen.uba.ar


Accepted: 26 January 2016 Published online: 21 March 2016 Supplemental materials deposited at Dryad: http://dx.doi.org/10.5061/dryad.55c3d


Introduction The origin and evolution of body plans lies in


the heart of evolutionary and developmental biology studies. From an evolutionary perspective, the body plans serve as a canvas on which the hierarchical genetic programs are challenged by the most diverse ecological situations to bring about this great improvisation around a theme we see as morphological diversity. In other cases, a body plan is versatile enough so as to be observed performing themost diverse repertoire of behaviors in a lineage with minimal changes. In either case, in understanding the evolution of a Bauplan,the primary goalof the scientist is to be capable of discriminating phylogenetic inertia from adaptation and the latter from exaptation in the observed diversity. Whether traits have predated, accompanied, or


© 2016 The Paleontological Society. All rights reserved.


followed the evolution of particular functions is the basic inference in order to establish the type of explanations required for morphological evolution. Anuran amphibians show a distinctive


Bauplan among tetrapods, with unique postcranial features that have usually been considered adaptations to a saltatory locomo- tion (Jenkins and Shubin 1998; Handrigan and Wassersug 2007;Přikryl et al. 2009). This Bauplan is characterized by a short body with a reduced number of presacral vertebrae (6–10), a single bony postsacral element (urostyle) lying between elongated ilia, paired limbs with fused zeugopodian elements, and relatively long hindlimbs with elongated proximal tarsals (Handrigan and Wassersug 2007). According to fossil evidence this Bauplan would have been achieved at least ca. 200Ma before the


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