Amphibian Skull Evolution: The Developmental and Functional Context of Simplification, Bone Loss and Heterotopy RAINER R. SCHOCH* Staatliches Museum für Naturkunde, Rosenstein 1, Stuttgart, Germany A combined effort of evo‐devo and paleontology seeks to address the old problem of the body plan within the relatively new framework of modularity and organismic integration (Schlosser and Wagner, 2004; Amundson, 2005 Carroll, 2005; Sánchez, 2012). Among the most enduring and tantalizing questions rank the following: Why are some body parts readily modified in evolution, whereas others remain so conservative? Which are the factors that give identity to structures that were conserved over hundreds of millions of years? How are anatomical units changed, duplicated, or lost—and why do some of them reappear after whole geological eras have passed? When fossils are considered, the main focus automatically shifts to the skeleton—informative, but sporadic soft anatomical preservation not withstanding. And skeletons provide rich data: the vertebrate skull for instance forms one of the most complicated structures preserved in the fossil record. The cranium has a rich and fascinating history, as well: the dermal skull of ABSTRACT Despite their divergent morphology, extant and extinct amphibians share numerous features in the timing and spatial patterning of dermal skull elements. Here, I show how the study of these features leads to a deeper understanding of morphological evolution. Batrachians (salamanders and frogs) have simplified skulls, with dermal bones appearing rudimentary compared with fossil tetrapods, and open cheeks resulting from the absence of other bones. The batrachian skull bones may be derived from those of temnospondyls by truncation of the developmental trajectory. The squamosal, quadratojugal, parietal, prefrontal, parasphenoid, palatine, and pterygoid form rudimentary versions of their homologs in temnospondyls. In addition, failure to ossify and early fusion of bone primordia both result in the absence of further bones that were consistently present in Paleozoic tetrapods. Here, I propose a new hypothesis explaining the observed patterns of bone loss and emargination in a functional context. The starting observation is that jaw‐closing muscles are arranged in a different way than in ancestors from the earliest ontogenetic stage onwards, with muscles attaching to the dorsal side of the frontal, parietal, and squamosal. The postparietal and supratemporal start to ossify in a similar way as in branchiosaurids, but are fused to neighboring elements to form continuous attachment areas for the internal adductor. The postfrontal, postorbital, and jugal fail to ossify, as their position is inconsistent with the novel arrangement of adductor muscles. Thus, rearrangement of adductors forms the common theme behind cranial simplification, driven by an evolutionary flattening of the skull in the batrachian stem. J. Exp. Zool. (Mol. Dev. Evol.) 9999B: XX–XX, 2014. © 2014 Wiley Periodicals, Inc. How to cite this article: SCHOCH RR. 2014. Amphibian skull evolution: The developmental and functional context of simplification, bone loss and heterotopy. J. Exp. Zool. (Mol. Dev. Evol.) 9999B:1–12. J. Exp. Zool. (Mol. Dev. Evol.) 9999B:1–12, 2014 Ã Correspondence to: Rainer R. Schoch, Staatliches Museum für Nat- urkunde, Rosenstein 1, D‐70191 Stuttgart, Germany. E‐mail: rainer.schoch@smns-bw.de Received 1 August 2014; Accepted 2 September 2014 DOI: 10.1002/.22599 Published online XX Month 2014 in Wiley Online Library (wileyonlinelibrary.com). RESEARCH ARTICLE © 2014 WILEY PERIODICALS, INC.