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Cover for ICB Chosen AKT11799.Indd Downloaded from https://academic.oup.com/iob/article-abstract/1/1/obz006/5418825 by U. of Florida Health Science Center Library user on 05 May 2020 ISSN 1540-7063 (PRINT) ISSN 1557-7023 (ONLINE) Integrative OrganismalA Journal of the Society Biology for Integrative and Comparative Biology academic.oup.com/icb Integrative Organismal Biology Integrative Organismal Biology,pp.1±–15 doi:10.1093/iob/obz006 A Journal of the Society for Integrative and Comparative Biology RESEARCH ARTICLE Downloaded from https://academic.oup.com/iob/article-abstract/1/1/obz006/5418825 by U. of Florida Health Science Center Library user on 05 May 2020 Crocodylian Head Width Allometry and Phylogenetic Prediction of Body Size in Extinct Crocodyliforms Haley D. O’Brien,1,* Leigha M. Lynch,† Kent A. Vliet,‡ John Brueggen,§ Gregory M. Erickson¶ and Paul M. Gignac2,* *Oklahoma State University Center for Health Sciences, 1111 West 17th Street, Tulsa, OK 74107, USA; †Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA; ‡Department of Biology, University of Florida, Gainesville, FL 32611, USA; §St. Augustine Alligator Farm Zoological Park, 999 Anastasia Blvd, St. Augustine, FL 32080, USA; ¶Department of Biological Sciences, Florida State University, 600 West College Avenue, Tallahassee, FL 32306, USA 1E-mail: [email protected] 2E-mail: [email protected] Synopsis Body size and body-size shifts broadly impact Synopsis Alometria de Largura da Cabec¸a de life-history parameters of all animals, which has made ac- Crocodilianos e Previsa˜o Filogene´tica de Tamanho curate body-size estimates for extinct taxa an important Corporal em Crocodilianos Extintos (Crocodylian Head component of understanding their paleobiology. Among Width Allometry and Phylogenetic Prediction of Body extinct crocodylians and their precursors (e.g., suchians), Size in Extinct Crocodyliforms) several methods have been developed to predict body size Tamanho corporal e mudanc¸as em proporc¸o˜es corporais from suites of hard-tissue proxies. Nevertheless, many afetam amplamente os paraˆmetros da biologia de todos os have limited applications due to the disparity of some animais, o que faz de estimativas precisas do tamanho major suchian groups and biases in the fossil record. corporal para ta´xons extintos um componente importante Here, we test the utility of head width (HW) as a broadly da compreensa˜o de sua paleobiologia. Entre os crocodilia- applicable body-size estimator in living and fossil nos extintos e seus precursores (por exemplo, os suchia- suchians. We use a dataset of sexually mature male and nos), va´rios me´todos foram desenvolvidos para prever o female individuals (n ¼ 76) from a comprehensive sample tamanho corporal a partir de conjuntos de pro´teses de of extant suchian species encompassing nearly all known tecido rı´gido. No entanto, va´rios desses conjuntos teˆm taxa (n ¼ 22) to develop a Bayesian phylogenetic model aplicac¸o˜es limitadas devido a` disparidade entre alguns for predicting three conventional metrics for size: body grandes grupos de crocodiliformes e vieses no registro mass, snout–vent length, and total length. We then use fo´ssil. Aqui, testamos a utilidade da largura da cabec¸a the model to estimate size parameters for a select series como um indicador de tamanho corporal aplica´vel a of extinct suchians with known phylogenetic affinity Crocodyliformes vivos e fo´sseis. Utilizamos um conjunto (Montsechosuchus, Diplocynodon, and Sarcosuchus). We de dados de indivı´duos machos e feˆmeas sexualmente ma- then compare our results to sizes reported in the literature duros (n¼76), de uma amostra abrangente de espe´cies to exemplify the utility of our approach for a broad array crocodı´licas viventes, abrangendo quase todos os taxa con- of fossil suchians. Our results show that HW is highly hecidos (n¼22), para desenvolver um modelo filogene´tico correlated with all other metrics (all R20.85) and is com- bayesiano para predizer treˆs morfometrias convencionais mensurate with femoral dimensions for its reliably as a para tamanho: massa corporal, comprimento da abertura body-size predictor. We provide the R code in order to nasal e comprimento total. Em seguida, usamos o modelo enable other researchers to employ the model in their own para estimar paraˆmetros de tamanho para um conjunto research. especı´fico de crocodiliformes extintos de afinidade filoge- ne´tica conhecida (Montsechosuchus, Diplocynodon, VC The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. 2 H. D. O’Brien et al. e Sarcosuchus). Comparamos enta˜o nossos resultados com os tamanhos relatados na literatura para exemplificar a utilidade de nossa abordagem para uma ampla gama de fo´sseis asia´ticos. Nossos resultados mostram que a largura da cabec¸a e´ altamente correlacionada com todas as outras Downloaded from https://academic.oup.com/iob/article-abstract/1/1/obz006/5418825 by U. of Florida Health Science Center Library user on 05 May 2020 me´tricas (R20.85, para todas) e e´compara´vel a dimenso˜es femorais como um preditor confia´vel de tamanho corporal. Fornecemos o co´digo R para permitir que outros pesqui- sadores utilizem o modelo em suas pro´prias pesquisas. Translated to Portuguese by J.P. Fontenelle (jp.fontenelle@- mail.utoronto.ca) Lynch et al. 2016), and length/circumference of the Introduction femur (Farlow et al. 2005; Young et al. 2011). For extant crocodylians (e.g., alligators, caimans, Although these proxies generally show strong corre- crocodiles, and gharials; Fig. 1), body size is an im- lations with body-size metrics, there are scenarios portant determinant of ecology, evolution, and fit- and circumstances that may preclude their utility. ness (Seebacher et al. 1999; Grigg and Seebacher For example, dental proxies may be less accurate 2000; McNab 2002), as well as a primary factor when the tooth position is unknown (Drumheller influencing a range of life-history and functional/ and Brochu 2014); head-length is most useful within performance traits. Individuals that reach larger sizes a single snout-shape ecomorph (Sereno et al. 2001 during maturation gain higher bite forces and tooth and references therein); and work on cranial pit- pressures (Erickson et al. 2003, 2012, 2014; Gignac depths remains preliminary (e.g., Lynch et al. and Erickson 2015, 2016) and gain access to a wider 2016). Femur length, the most commonly used met- variety of prey items (Abercrombie 1989; ric, is difficult to reliably apply to studies of the fossil Abercrombie et al. 2001). Larger individuals gener- record, as extant crocodylians are semi-aquatic and ally show higher survivorship and reproductive rates, many of their ancestors inhabited either fully terres- thus linking obtainment of larger within-population trial or fully marine habitats (Young et al. 2011). body sizes to increased fitness (Dodson 1975; Webb Differences in habitat and posture create differential and Manolis 1989; Grenard 1991). Likewise, hetero- mechanical loading regimes (Alexander 1989; Bonner chronic deviations from ancestral body sizes (Gignac 2006; Young et al. 2011), which can therefore render and O’Brien 2016; Godoy et al. 2018) can be largely femur-size-based reconstructions tenuous between linked to evolutionary shifts in craniodental dispar- taxa, as well as across ecologies not represented ity. Thus, body size in general—and body-size shifts, among modern crocodylians. Similarly, the use of specifically—are significant for not only influencing femoral circumference is best limited to intraspecific modern crocodylian community dynamics and con- comparisons (e.g., developmental mass extrapolation; servation, but can provide insights into the paleo- Erickson and Tumanova 2000). Finally, many of ecology of extinct Crocodyliformes (see Turner and these proxies are restricted in paleontological con- Sertich 2010) and their archosaurian relatives, as texts by taphonomy. Crocodyliforms commonly well. For these reasons, understanding crocodylian inhabited fluvial, costal, and shallow marine environ- allometry has been a perennial goal in vertebrate ments, which favor post-depositional compression paleontology. (Reisdorf et al. 2012; Orr et al. 2016) and typically Numerous methods have been developed for the preclude three-dimensional (3D) morphological data prediction of body-size parameters in crocodylians, collection of body-size proxies. To overcome these such as body mass, snout–vent length (SVL), and total issues, we propose the use of head width (HW), length (TL), from suites of hard-tissue proxies. These measured as the linear distance between the lateral include vertebral column proxies (Seebacher et al. surfaces of the left and right jaw joints, as a viable 1999; Young et al. 2016), pelvic dimensions (Prieto- alternative metric. Marquez et al. 2007), dental variables (Njau and HW has been used as a body-size proxy on a case- Blumenschine 2006, 2011), head length (Webb and by-case basis in a handful of studies examining ex- Messel 1978; Sereno et al. 2001; Young et al. 2011, tinct crocodyliforms (e.g., Kley et al. 2010; Gignac 2016), depth of non-trigeminal cranial pits (Mook and O’Brien 2016). However, the scope of its utility
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