Pectoral Fin Morphology of Batoid Fishes (Chondrichthyes: Batoidea): Explaining Phylogenetic Variation With Geometric Morphometrics Oliver Franklin, 1 * Colin Palmer, 2 and Gareth Dyke 3 1 Department of Integrative Biology, University of Guelph, Canada 2 Department of Ocean and Earth Science, University of Bristol, UK 3 Department of Earth Science, University of Southampton, UK ABSTRACT The diverse cartilaginous fish lineage, Batoidea (rays, skates, and allies), sister taxon to sharks, comprises a huge range of morphological diversity which to date remains unquantified and unexplained in terms of evolution or locomotor style. A recent molecular phy- logeny has enabled us to confidently assess broadscale aspects of morphology across Batoidea. Geometric mor- phometrics quantifies the major aspects of shape varia- tion, focusing on the enlarged pectoral fins which characterize batoids, to explore relationships between ancestry, locomotion and habitat. A database of 253 speci- mens, encompassing 60 of the 72 batoid genera, reveals that the majority of morphological variation across Batoi- dea is attributable to fin aspect-ratio and the chordwise location of fin apexes. Both aspect-ratio and apex location exhibit significant phylogenetic signal. Standardized independent linear contrast analysis reveals that fin aspect-ratio can predict locomotor style. This study pro- vides the first evidence that low aspect-ratio fins are cor- related with undulatory-style locomotion in batoids, whereas high aspect-ratio fins are correlated with oscilla- tory locomotion. We also show that it is phylogeny that determines locomotor style. In addition, body- and caudal fin-locomotors are shown to exhibit low aspect-ratio fins, whereas a pelagic lifestyle correlates with high aspect- ratio fins. These results emphasize the importance of phylogeny in determining batoid pectoral fin shape, how- ever, interactions with other constraints, most notably locomotor style, are also highlighted as significant. J. Morphol. 000:000–000, 2014. V C 2014 Wiley Periodicals, Inc. KEY WORDS: divergence; swimming; oscillatory; undulatory INTRODUCTION Batoidea, the sister lineage of sharks, commonly known as rays and skates, contains around 630 species (e.g., Compagno, 1999; Aschliman et al., 2012) which display diverse morphologies and sizes: Lengths range from 100 mm to over 7000 mm (Compagno, 1999). Their dorsoventrally flattened bodies with enlarged pectoral fins connected to the head and trunk form, generally, a disk shape (McEachran and de Carvalho, 2002); however, wing-like forms (e.g., Eagle Rays) and shark-like forms (e.g., Guitarfishes) add to this range of morphologies (Compagno, 1999; Rosenberger, 2001). A recent molecular phylogeny has clarified relation- ships within Batoidea (Aschliman, 2011; Aschliman et al., 2012), allowing informed analyses of broad- scale morphological variation. In this phylogeny, Rajoidei were revealed as sister taxon to all other batoids, implicating a disk-like ancestral form, rather than a shark-like form, as previously thought. Across Batoidea substantial variation in morphology exists yet, to date, few have attempted to explain why or to quantitatively assess relation- ships between morphology, ancestry and habitat. A recent study has demonstrated the utility of these assessments in showing that batoid pelvic girdle morphology can be a useful predictor of phylogeny and punting, a style of substrate locomotion (Ekstrom and Kajiura, 2013). Batoid pectoral fins are highly flexible, con- strained only at the base, and used for manoeu- vrability, stabilization, and propulsion to varying degrees across the phylogeny (Parson et al., 2011). Batoids swim with different styles, categorized as body and caudal fin (BCF), and median and paired-fin (MPF) locomotion (Blake, 2004). Some batoids appear to swim exclusively within one style (i.e., Pristoidei and some Torpedinoidei with BCF; Stingrays and Rajoidei with MPF) whereas others (e.g., Guitarfishes) use both to varying degrees (Compagno, 1990; Rosenberger, 2001; Rosenblum et al., 2011). Batoids using MPF loco- motion create a chordwise-traveling wave of Additional Supporting Information may be found in the online version of this article. *Correspondence to: Oliver Franklin; Department of Integrative Biology, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada. E-mail: ofrankli@uoguelph.ca Received 25 November 2013; Revised 7 March 2014; Accepted 13 April 2014. Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jmor.20294 V C 2014 WILEY PERIODICALS, INC. JOURNAL OF MORPHOLOGY 00:00–00 (2014)