Journal of Anatomy

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Journal of Anatomy

J. Anat. (2017) 230, pp325--336 doi: 10.1111/joa.12557

Reconstruction of body cavity volume in terrestrial tetrapods Marcus Clauss,1 Irina Nurutdinova,2 Carlo Meloro,3 Hanns-Christian Gunga,4 Duofang Jiang,2 Johannes Koller,2 Bernd Herkner,5 P. Martin Sander6 and Olaf Hellwich2

1Clinic for Zoo Animals, Exotic Pets and Wildlife, University of Zurich, Zurich, Switzerland 2Computer Vision and Remote Sensing, Technical University Berlin, Berlin, Germany 3Research Centre in Evolutionary Anthropology and Palaeoecology, Liverpool John Moores University, Liverpool, UK 4ChariteCrossOver - Institute of Physiology, Berlin, Germany 5Senckenberg Research Institute and Natural History Museum, Frankfurt (Main), Germany 6Steinmann Institute of Palaeontology, University of Bonn, Bonn, Germany

Abstract

Although it is generally assumed that herbivores have more voluminous body cavities due to larger digestive tracts required for the digestion of plant fiber, this concept has not been addressed quantitatively. We estimated the volume of the torso in 126 terrestrial tetrapods (synapsids including basal synapsids and mammals, and diapsids including birds, non-avian dinosaurs and reptiles) classified as either herbivore or carnivore in digital models of mounted skeletons, using the convex hull method. The difference in relative torso volume between diet types was significant in mammals, where relative torso volumes of herbivores were about twice as large as that of carnivores, supporting the general hypothesis. However, this effect was not evident in diapsids. This may either reflect the difficulty to reliably reconstruct mounted skeletons in non-avian dinosaurs, or a fundamental difference in the bauplan of different groups of tetrapods, for example due to differences in respiratory anatomy. Evidently, the condition in mammals should not be automatically assumed in other, including more basal, tetrapod lineages. In both synapsids and diapsids, large animals showed a high degree of divergence with respect to the proportion of their convex hull directly supported by bone, with animals like elephants or Triceratops having a low proportion, and animals such as rhinoceros having a high proportion of bony support. The relevance of this difference remains to be further investigated. Key words: anatomy; carnivory; digestive tract; herbivory; photogrammetry; ribcage.

Introduction herbivores are typically considered to be particularly long and/or voluminous (Cuvier & Dumeril, 1838; Orr, 1976). Tetrapods have diversified into an enormous variety of Differences in the length of the intestinal tract according body forms that display convergent evolution at various to diet have been repeatedly shown for fish (Wagner et al. levels of organismal design. For example, the gastrointesti- 2009; Karachle & Stergiou, 2010), lizards (O’Grady et al. nal tract (GIT) is adapted in size and shape to an animal’s 2005), and in other animal lineages such as invertebrates diet (Cuvier & Dumeril, 1838; Treves, 1886). In broad terms, (Griffen & Mosblack, 2011), but not convincingly in birds the diets of herbivorous animals are less easily digested (DeGolier et al. 1999; Lavin et al. 2008). In mammals, similar than those of carnivores, and require both the presence of evidence is questionable and mostly limited to small body a large number of symbiotic gut microbes and time for sizes (Barry, 1977; Wang et al. 2003). Chivers & Hladik these microbes to perform their digestive function (Stevens (1980) calculated lower volumes of the combined stomach, & Hume, 1998). Therefore, in order to accommodate this caecum and colon (from linear GIT dimensions) for mam- large microbiome, and to delay digesta passage, the GITs of malian carnivores as compared with herbivores of similar cubic body length, and Schiek & Millar (1985) found more GIT tissue mass in herbivorous than carnivorous small mam- Correspondence Marcus Clauss, Clinic for Zoo Animals, Exotic Pets and Wildlife, Vet- mals up to about 1 kg. However, Starck (1982) doubted that suisse Faculty, University of Zurich, Winterthurerstr. 260, 8057 Zurich, trophic groups can really be distinguished by the length of Switzerland. E: [email protected] their intestinal tracts, and Lavin et al. (2008) did not detect Accepted for publication 22 September 2016 a difference in the small intestinal length or volume in small Article published online 4 November 2016 mammals of different diet types. A major difficulty in such

comparisons may be that the most relevant characteristic, a amphibians. Of these, 31 were categorized as carnivores and 95 as measure of gut fill, is available for a large number of herbi- herbivores (Table S1). vore species (Clauss et al. 2013) because their digestive tract For reconstruction from multiple images, we first made a series usually always contains a relatively constant amount of of overlapping photographs from a large number of positions in a circle around the specimen. The images were acquired with a digesta, but is not similarly available for carnivores where Canon 600D DSLR camera, in most of the cases mounted on a tri- gut contents may vary enormously (Potgieter & Davies-Mos- pod. For the majority of reconstructions we used an image resolu- tert, 2012). tion of 2592 9 1728 pixels, because we found this quality to be Nevertheless, a voluminous torso that can host a volumi- sufficient for our purposes. The 3D models were computed from nous GIT is considered a prerequisite for high-fiber her- these image sequences using publicly available structure-from- bivory (Hotton et al. 1997), and the appearance of the motion software Visual SFM (Wu, 2007, 2012; Wu et al. 2011) and torso – as judged from articulated skeletons or the shape of Bundler (Snavely et al. 2006), and multiview stereo software PMVS2 (Furukawa & Ponce, 2010). The resulting reconstructions (Fig. 1a) ribs – is considered an indication for a diet type in fossil and were then scaled to true size. For this purpose, we measured several extant tetrapods (Hotton et al. 1997; Sues & Reisz, 1998; distances on the skeletal specimens or its location (such as the Reisz & Sues, 2000), including hominids (Bryant, 1915; Aiello length of boards on which specimens were mounted), identified & Wheeler, 1995). However, quantitative tests of this con- them in the point cloud and scaled the reconstruction accordingly. cept are lacking. In this manuscript, we intended to test We cleaned the point clouds from the background, from support- whether the volume of the body cavity (coelomic or the ing structures (such as poles on which bones were mounted) that combination of thorax and abdomen), as reconstructed would interfere with the reconstruction of the convex hull of the torso, and reconstruction artefacts (Fig. 1b). The 3D reconstructions from mounted skeletons of various terrestrial tetrapods, dif- used from previous sources resembled, in their state, those pro- fers systematically with the diet typically ascribed to these duced during the present study at this stage. species. We hypothesized herbivores to have larger body From this stage onwards, the workflow was identical for 3D cavities for a given body size than carnivores. Additionally, reconstructions from previous sources and the ones generated for we expected that among herbivorous non-avian dinosaurs, the present study. Side views of all 3D reconstructions used in this species without adaptations for ingesta particle size com- study are given as Figs S1–S5, and the original 3D reconstructions minution (such as a grinding mastication or a gizzard) can be accessed at Morphobank (www.morphobank.org, Project should have more voluminous body cavities than species P2404). The torsos were segmented out using open source software Meshlab (Cignoni et al. 2008). In doing so, care was taken to with such adaptations, because a voluminous gut and the remove from torsos all aspects that do not contribute to the volume corresponding long digesta retention times can compensate of the body cavity, such as the spinal processes of the vertebrae. for a lack of particle size reduction (Clauss et al. 2009; Hum- Then, the volumes of convex hulls (Sellers et al. 2012; Brassey & Sell- mel & Clauss, 2011). ers, 2014; Fig. 1c) of the torsos were calculated using Point Cloud Library (Aldoma et al. 2012). Five torsos that were reconstructed Materials and methods mainly from one side were digitally mirrored (indicated in Table S1). In eight cases, the convex hull of the torso was not plausi- We compiled a dataset of digital 3D models of 11 mounted mam- ble and included additional space, for example lateral to the ribc- mal skeletons available from Sellers et al. (2012), from 19 previously age; in these cases, the torso was digitally cut into two parts performed scans (Gunga et al. 1999, 2007, 2008; Stoinski et al. (typically at the level of the last rib) and the convex hull calculated 2011), and additionally from our own reconstruction of 96 speci- for each part, and the resulting individual volumes added together mens based on photogrammetry. If, for a species available from (specimens indicated in Table S1). Sellers et al. (2012) we also had a skeleton model of our own, we In comparative analyses, it is necessary to correct for body size. used our own model. All skeletal material was photographed with Typically, this is done using body mass (Peters, 1983; Calder, 1996; permission of the respective museum or institution. Although Sibly et al. 2012), and alternatives are mostly only resorted to if rarely discussed in detail (Bates et al. 2009b; Hutchinson et al. body mass itself is not available. Body mass measures were not 2011; Sellers et al. 2012; Brassey & Sellers, 2014), a typical issue in available for the specimens from which the skeletons for the pre- dealing with mounted skeletons is the quality of the mount; when- sent study had been taken and, therefore, a skeletal proxy for body ever discussed, the positioning of the ribs and the intervertebral mass had to be found. However, also methodological considera- spaces are among the characteristics considered particularly critical. tions argue against using body mass in this case: the volume of the Because for our study the torso was the main target, we did not torso represents a major proportion of overall body mass and, focus on the quality of other mounted parts (such as the neck, therefore, differences in torso volume most certainly are reflected head or tail). For the torso, we only chose mounts in which the ribs in body mass differences already. ‘Correcting’ for body mass (rather were in a fixed position (as opposed to ‘dangling loosely’), where than for body size) would hence most likely diminish any potential the rib cage did not have a ‘compressed’ appearance (such as in trophic signal. On the other hand, body mass itself might serve as a mounts where the osseous ventral ends of the ribs appeared too proxy for body cavity volume when compared with another size close to allow for a cartilaginous part or a sternum), and where the proxy. Please refer to Supporting Information for a more detailed articular facets of the ribs and the thoracic vertebrae apposed each discussion and a demonstration of this concept in Tables S3 and S4. other. This resulted in 126 digital skeletons of tetrapods including Because body mass itself is not a useful proxy for the question of 86 synapsids (10 ‘mammal-like reptiles’ or basal synapsids and 76 our study, mass reconstructions from convex hull volumes of the fossil and extant mammals), 38 diapsids (six extant birds, 27 non- complete skeletons were not considered a valid option. Given the avian dinosaurs, five fossil and extant reptiles), and two nature of our data, the most promising candidate was femur length

Fig. 1 Illustration of the image processing for Hexaprotodon liberiensis. The raw data (a) were scaled, cleaned of background and supporting structures (b). The torso was isolated, removing structures that would inﬂuence the convex hull in a way not corresponding to the actual body cavity, for example the spinal processes. Then the convex hull was calculated (c). Note the de absence of ribs in the area where they had been covered by the scapula. Finally, the femur was isolated (d) to measure its length. The convex hull was later divided (e) into parts that are supported by bone (red dots) and parts that are not (green dots), to estimate the ‘free-hull ratio’.

(Campione & Evans, 2012). The femur length was calculated as the not). A higher ‘free-hull ratio’ indicates that a larger proportion of length of the bounding box of the thighbone (Fig. 1d). For this, we the body cavity is delineated by soft tissue (i.e. the abdominal wall). aligned the bone to the axis using principal component analysis Species were classified as herbivores or carnivores (thus omitting (Jolliffe, 2002). The first principal axis, which is the axis of the lar- more subtle categories such as omnivores) based on the main cate- gest variation of the data, for the thighbone usually corresponds to gory of diet items, using a variety of sources (Walls, 1981; Losos & the main direction in which the bone is elongated. Greene, 1988; Rand et al. 1990; Weishampel et al. 1990; Reisz & Sues, As a proxy for the proportion of the convex hull of the abdomi- 2000; Reisz, 2006; Wilman et al. 2014), including the Paleobiology nal cavity that was not ‘supported’ by bony structures (i.e. a proxy Database (www.paleobiodb.org). Herbivorous dinosaurs were classi- for how much of the abdominal wall reconstructed as the convex fied as chewers or non-chewers following Weishampel et al. (1990), hull spanned ‘open distances’ in the mounted skeleton), we calcu- and considering sauropods as neither chewing nor grinding ingesta lated the ‘free-hull ratio’. We sampled 8000 evenly distributed in a gizzard (Wings & Sander, 2007; classifications in Table S1). points (with constant distance between the points for a given skele- We analyzed the influence of diet on the volume of the torso or ton) on the convex hull, labeled every sample of it as ‘supported’ or the free-hull ratio as related to femur length, accounting for phy- ‘non-supported’ (purple and green dots, respectively, in Fig. 1e), logeny based on a tree constructed from literature data [the basic and calculated the ratio of the number of ‘non-supported’ points to topology of tetrapod groups is based on tree of life project (Mad- the number of all points. Labels were ascribed by the following pro- dison & Schulz, 2007) supplemented with specific references]. See cedure. For each 3D point on the skeleton we determined the clos- Supporting Information for a detailed description of Data S1. est point on the convex hull and marked all sampled points within Data were evaluated as a certain distance of it as ‘supported’. This distance had to be adapted to the size of the animal; we took 3% of the diagonal of Torso volume ðcm3Þ¼a ðfactorÞ Femur lengthb the bounding box of the total animal model as determined by prin- and cipal component analysis (Jolliffe, 2002). We used the region growing method from Point Cloud Library (Aldoma et al. 2012) to cluster Free-hull ratio ¼ a ðfactorÞ Femur lengthb the points with the same labels together. We took the largest cluster of ‘non-supported’ points, which usually corresponded to the using log-transformed data and diet type (carnivore or herbi- area of the abdominal wall (and discarded the cases when it did vore), chewing type (in non-avian dinosaur herbivores: chewers

and non-chewers) or various taxonomic factors in addition, as with or without a grinding mastication (Table 1, as exempli- indicated in Tables 1 and 2. When using an additional factor, fied by the non-chewers Giraffatitan, Stegosaurus and Euo- first a model that included the femur length-factor interaction plocephalus compared with the chewer Iguanodon in was used; if the interaction was not significant, the same model Fig. 2b). without the interaction was used. For example, if the (factor) term was coded, for diet, as carnivore = 0 and herbivore = 1, The relationship of the free-hull ratio and femur length then the resulting factor estimate z can be translated into ‘her- was generally negative, indicating that larger animals had a bivores have a z times larger torso volume than carnivores’. To lower proportion of their body cavity delineated by soft tis- account for the phylogenetic non-independence of data, analy- sue (Table 2). This was evident in both synapsids (Fig. 3a) ses were performed using phylogenetic generalized least and diapsids (Fig. 3b). Diet did not have an effect on this k squares (PGLS). The phylogenetic signal ( ) was estimated using relationship (Table 2). Variation in the free-hull ratio maximum likelihood (Revell, 2010). k can vary between 0 (no increased with body size (Fig. 3a,b), some animals having a phylogenetic signal) and 1 (strong phylogenetic signal; similarity among species scales in proportion to their shared evolutionary low contribution of bony support to the delineation of the time), i.e. we assumed Pagel’s correlation structure (Pagel, 1999; body cavity (such as proboscideans amongst mammals in Freckleton et al. 2002). Statistical tests were performed using Fig. 3a or Triceratops among non-avian dinosaurs in the package CAPER (Orme et al. 2010) in R 2.15.0 (Team RDC, Fig. 3b), and some animals with a ribcage nearly delineat- 2011). Results of analyses with ordinary least squares (OLS), i.e. ing the complete ventral body cavity (such as giraffe or rhi- without accounting for the phylogenetic structure of the data, noceros among mammals in Fig. 3a or Diplodocus among using the package nlme (Pinheiro et al. 2011), are also reported. non-avian dinosaurs in Fig. 3b). Note that for some analyses that specifically address a question linked to phylogeny, such as the question whether basal synapsids differ from all other groups, analyses that ‘correct’ for the Discussion phylogenetic relationships cannot provide a relevant answer. The significance level was set to 0.05. Based on the general geo- The hypothesis that herbivores have more voluminous body metric relationship between a length and a volume measure, cavities than carnivores was confirmed for the mammals in we expected torso volumes to scale approximately with femur our dataset. However, no diet effect was detected in diap- length to the cubic power (length3). sids and non-avian dinosaurs. Considering the overrepresen- tation of mammals in our dataset, and in particular the low Results number of birds, reptiles and carnivorous non-avian dinosaurs, this finding may be due to a restricted sample size, Generally, torso volume scaled to femur length at an expo- and should be considered explorative for these groups. In nent that included the cubic power (i.e. femur length3.0)in this respect, we hope that making our digital skeletons the 95% confidence interval, as expected for a geometric accessible at Morphobank will facilitate similar tests with scaling of a volume–distance relationship (Table 1). This increased sample sizes as more digital skeletons become overall scaling did not differ between synapsids and diap- available. However, individual findings, such as a particu- sids (Table 1). However, the basal synapsids had torso vol- larly large body cavity in a carnivorous varanid (Fig. 2b), umes about 3.5 times larger than all the other clades possibly indicate that the diet effect observed in mammals (Table 1; Fig. 2a). need not necessarily be reflected in other groups. In the overall dataset, diet had a significant effect on the Several important methodological constraints of our torso volume, with herbivores having about 1.5 times larger study need to be mentioned. The use of femur length as a torso volumes than carnivores (Table 1). This was due to a proxy for body size might not be considered ideal, also cleareffectofdietinmammals– thelargestcladeinour because measurements were not taken on the original dataset. In mammals, herbivores again had about 1.5 times skeletons but, to grant consistency across all 3D models larger torso volumes than carnivores (Table 1; Fig. 2a). We used, on the digitally isolated 3D reconstruction of the did not have a sufficient number of basal synapsids to test femur. Inaccurate measurements, such as underestimation for a difference between diet types; the visual pattern does of femur length due to overlap of other skeletal structures not suggest a clear distinction between carnivores and her- such as the acetabulum, may evidently occur. Yet, the ques- bivores in this group (Fig. 2a). tion about a more suitable proxy than femur length is diffi- In contrast to mammals, there was no significant effect of cult to answer. As stated in the methods, because the torso diet on torso volume in all diapsids or in non-avian dino- volume represents a major proportion of overall body mass, saurs only (Table 1; Fig. 2b). We did not have a sufficient it appears probable that differences in the torso volume–fe- number of birds or reptiles to test for a difference between mur length relationship should be mirrored in the body diet types in these diapsid clades; the visual patterns, how- mass–femur length relationship. See Supporting Informa- ever, did not suggest a clear distinction between carnivores tion for an explorative analysis suggesting support for this and herbivores in these groups, nor in non-avian dinosaurs hypothesis (using literature body mass data in connection (Fig. 2b). Among herbivorous non-avian dinosaurs, there with our own measurements). An even more important was no difference in relative torso volume between species constraint of studies such as ours is the quality of the

Table 1 Results of statistical analyses according to torso volume = a (factor) femur lengthb (and the corresponding factor 9 femur length interaction) in OLS and PGLS.

Stats k a (95% CI) Pb(95% CI) P Factor† (95% CI) P Interaction‡ P

All specimens (n = 126) OLS (0) 2.23 (1.38, 3.59) 0.001 2.97 (2.84, 3.11) < 0.001 ––– PGLS 0.906** 5.20 (2.47, 10.93) < 0.001 3.04 (2.88, 3.21) < 0.001 ––– Synapsid/Diapsid OLS (0) 1.75 (0.97, 3.16) 0.067 3.01 (2.86, 3.15) < 0.001 1.21 (0.92, 1.60) 0.178 n.s. PGLS 0.904** 7.59 (2.94, 19.61) < 0.001 3.03 (2.87, 3.20) < 0.001 0.70 (0.41, 1.22) 0.215 n.s. Basal synapsid OLS (0) 1.70 (1.13, 2.57) 0.013 3.02 (2.90, 3.13) < 0.001 3.64 (2.52, 5.26) < 0.001 n.s. PGLS 0.907** 5.29 (2.51, 11.17) < 0.001 3.04 (2.87, 3.21) < 0.001 0.81 (0.47, 1.40) 0.449 n.s. Diet OLS (0) 1.94 (1.21, 3.09) 0.007 2.92 (2.78, 3.05) < 0.001 1.57 (1.19, 2.08) 0.002 n.s. PGLS 0.872** 4.81 (2.39, 9.66) < 0.001 3.01 (2.84, 3.17) < 0.001 1.48 (1.13, 1.95) 0.005 n.s. All carnivores (n = 31) OLS (0) 2.38 (0.92, 6.16) 0.085 2.85 (2.55, 3.15) < 0.001 ––– PGLS 0.922* 8.93 (2.66, 29.95) 0.001 2.79 (2.45, 3.13) < 0.001 ––– All herbivores (n = 95) OLS (0) 2.83 (1.64, 4.90) < 0.001 2.94 (2.79, 3.08) < 0.001 ––– PGLS 0.918** 5.74 (2.58, 12.74) < 0.001 3.06 (2.88, 3.25) < 0.001 ––– Synapsids (n = 86) OLS (0) 1.71 (0.89, 3.28) 0.112 3.07 (2.87, 3.26) < 0.001 ––– PGLS 0.926** 4.47 (2.14, 9.34) < 0.001 3.13 (2.93, 3.33) < 0.001 ––– Basal synapsid OLS (0) 1.35 (0.78, 2.33) 0.285 3.09 (2.93, 3.26) < 0.001 3.45 (2.34, 5.08) < 0.001 n.s. PGLS 0.920** 1.68 (0.32, 8.73) 0.539 3.13 (2.93, 3.33) < 0.001 2.66 (0.61, 11.66) 0.199 n.s. Diet OLS (0) 1.51 (0.81, 2.81) 0.202 2.98 (2.79, 3.18) < 0.001 1.72 (1.23, 2.40) 0.002 n.s. PGLS 0.926** 13.12 (4.10, 42.02) < 0.001 2.73 (2.35, 3.10) < 0.001 0.31 (0.09, 1.14) 0.082 0.028 Basal synapsids (n = 10) OLS (0) 0.31 (0.01, 7.79) 0.499 3.96 (2.94, 4.98) < 0.001 ––– PGLS 0 0.50 (0.02, 12.99) 0.685 3.83 (2.77, 4.89) < 0.001 ––– Mammals (n = 76) OLS (0) 1.45 (0.84, 2.50) 0.189 3.07 (2.91, 3.24) < 0.001 ––– PGLS 0.703** 1.44 (0.72, 2.88) 0.300 3.07 (2.90, 3.24) < 0.001 ––– Diet OLS (0) 1.12 (0.70, 1.81) 0.640 2.98 (2.84, 3.12) < 0.001 2.08 (1.58, 2.73) < 0.001 n.s. PGLS 0.476 1.19 (0.63, 2.24) 0.598 3.02 (2.86, 3.19) < 0.001 1.56 (1.06, 2.29) 0.027 n.s. Mammal carnivores (n = 18) OLS (0) 1.93 (0.89, 4.19) 0.117 2.79 (2.53, 3.05) < 0.001 ––– PGLS 0 1.91 (0.88, 4.17) 0.122 2.80 (2.54, 3.05) < 0.001 ––– Mammal herbivores (n = 58) OLS (0) 1.95 (1.09, 3.49) 0.028 3.03 (2.86, 3.20) < 0.001 ––– PGLS 0.755 1.25 (0.55, 2.83) 0.592 3.15 (2.95, 3.35) < 0.001 ––– Diapsids (n = 38) OLS (0) 2.01 (0.95, 4.23) 0.075 2.96 (2.78, 3.15) < 0.001 ––– PGLS 0 2.88 (1.24, 6.69) 0.019 2.88 (2.68, 3.09) 0.127 ––– Diet OLS (0) 1.84 (0.85, 3.97) 0.131 2.94 (2.75, 3.13) < 0.001 1.25 (0.78, 2.03) 0.363 n.s. PGLS 0 2.32 (0.95, 5.67) 0.074 2.87 (2.66, 3.07) < 0.001 1.42 (0.84, 2.38) 0.197 n.s. Diapsid carnivores (n = 8) OLS (0) 2.18 (0.53, 8.99) 0.324 2.89 (2.50, 3.29) < 0.001 ––– PGLS 1*** 1.72 (0.43, 6.79) 0.471 3.01 (2.66, 3.37) < 0.001 ––– Diapsid herbivores (n = 30) OLS (0) 2.12 (0.84, 5.39) 0.124 2.96 (2.74, 3.18) < 0.001 ––– PGLS 0 3.31 (1.21, 9.09) 0.027 2.86 (2.62, 3.11) < 0.001 –––

Table 1. (continued)

† ‡ Stats k a (95% CI) Pb(95% CI) P Factor (95% CI) P Interaction P

Non-avian dinosaurs (n = 27) OLS (0) 2.87 (0.67, 12.30) 0.168 2.89 (2.56, 3.21) < 0.001 ––– PGLS 0.651** 2.05 (0.54, 7.83) 0.303 2.96 (2.65, 3.27) < 0.001 ––– Diet OLS (0) 2.15 (0.47, 9.84) 0.333 2.89 (2.57, 3.21) < 0.001 1.37 (0.81, 2.31) 0.248 n.s. PGLS 0.604 1.43 (0.32, 6.49) 0.647 2.97 (2.66, 3.29) < 0.001 1.40 (0.74, 2.66) 0.317 n.s. Non-avian dinosaur herbivores (n = 23) OLS (0) 3.19 (0.68, 14.86) 0.155 2.87 (2.53, 3.22) < 0.001 ––– PGLS 0.639 2.00 (0.47, 8.45) 0.358 2.97 (2.64, 3.31) < 0.001 ––– Chewer OLS (0) 2.87 (0.63, 13.05) 0.189 2.84 (2.50, 3.18) < 0.001 1.39 (0.87, 2.23) 0.187 n.s. PGLS 0.649 2.14 (0.31, 14.61) 0.445 2.97 (2.60, 3.34) < 0.001 0.96 (0.45, 2.02) 0.907 n.s.

Torso volume in cm3, femur length in cm. *k significantly different from 0. **k significantly different from 0 and 1. ***k not significantly different from 0 and 1. † Factor coding: diet (carnivore = 0, herbivore = 1), synapsid/diapsid (diapsid = 0, synapsid = 1), basal synapsid (no basal synapsid = 0, basal synapsid = 1), chewer (chewer = 0, non-chewer = 1). ‡ Models were calculated with interaction term first; if this was not significant, the model was again calculated without the interaction term; estimates for the factor in this table always represent the models where either the interaction was significant or excluded. OLS, ordinary least squares; PGLS, phylogenetic generalized least squares.

skeletal mounts used (Bates et al. 2009b; Hutchinson et al. body design as endothermy. Heterogeneity might even 2011; Sellers et al. 2012; Brassey & Sellers, 2014; Claessens, have occurred on the level of metabolism between dino- 2015). Incorrect reconstructions of rib shape and rib posi- saur lineages. Additionally, the respiratory system of diap- tion, exacerbated by a lack of conservation of cartilaginous sids with its heterogenous lung, pneumatized bones and components of the torso (such as costal and sternal carti- space occupied by variable coelomic air sacs, and unidirec- lage and intervertebral disks) or small osseous structures tional air flow (O’Connor & Claessens, 2005; Perry et al. (such as components of the pectoral girdle), will greatly 2011; Farmer, 2015) may exert additional selective pres- influence any measurements derived from skeletal mounts, sures on the shape of the torso (Claessens, 2015) that are and are more likely to occur the less familiar a curator is not yet fully understood. A specific prediction about a dif- with the species in question. Inherently, this means that fos- ference in the body cavity volume between herbivorous sil specimens underlie a greater uncertainty in this respect non-avian dinosaurs with and without adaptations for than representatives of extant species. Ultimately, concur- ingesta particle size reduction (Hummel & Clauss, 2011; rent measurements of gut tissue, gut content and body Clauss et al. 2013) could also not be confirmed in the pre- mass as well as body cavity volume in healthy, non-fasted sent study. animals will be required to empirically prove the assump- In contrast, the general concept of larger body cavity vol- tion that extant herbivores carry more weight at similar umes that accommodate larger guts in herbivores is sup- body size than extant carnivores. ported for mammals. Reasons for the distinct diet difference The absence of a diet effect in non-avian dinosaurs in mammals may be the large sample size, the large number could on the one hand reflect these difficulties in correctly of extant specimens (in which constructing correct skeletal reconstructing skeletal appearance in fossil organisms, in mounts may be easier), and the fact that mounts of fossil particular the rib cage (Bates et al. 2009a; Claessens, forms can be more easily constructed with extant species as 2015). On the other hand, the absence of a clear diet sig- reference guidelines. Additionally, the high overall mam- nal in diapsids could be linked to the bauplan hetero- malian level of metabolism and efficient cursoriality, which geneity within lineages (e.g. bipedal vs. quadrupedal, might have led to an evolutionary arms race of predators which in non-avian dinosaurs mostly mirrors the herbi- and prey (Lovegrove, 2001) that represented a high level of vore/carnivore dichotomy); or due to an ectothermic or selective pressure for an optimized torso volume, may be mesothermic metabolism in reptiles and (some) non-avian responsible for the clearer separation of diet types. Given dinosaurs (Grady et al. 2014; Werner & Griebeler, 2014) that basal synapsids had relatively higher torso volumes that did not exert a similar selective pressure on optimal than mammals, one could hypothesize an evolutionary

Table 2 Results of statistical analyses according to free-hull ratio = a (factor) femur lengthb (and the corresponding factor 9 femur length interaction) in OLS and PGLS.

Stats k a (95% CI) Pb(95% CI) P Factor† (95% CI) P Interaction‡ P

All specimens (n = 126) OLS (0) 0.37 (0.29, 0.48) < 0.001 0.19 (0.26, 0.11) < 0.001 ––– PGLS 0.693** 0.32 (0.21, 0.49) < 0.001 0.17 (0.27, 0.06) 0.002 ––– Synapsid/Diapsid OLS (0) 0.38 (0.27, 0.52) < 0.001 0.19 (0.27, 0.11) < 0.001 0.99 (0.85, 1.15) 0.891 n.s. PGLS 0.687** 0.28 (0.16, 0.47) < 0.001 0.16 (0.27, 0.06) 0.003 1.16 (0.84, 1.61) 0.373 n.s. Basal synapsid OLS (0) 0.39 (0.30, 0.50) < 0.001 0.19 (0.27, 0.12) < 0.001 0.85 (0.67, 1.08) 0.182 n.s. PGLS 0.694** 0.32 (0.21, 0.49) < 0.001 0.17 (0.27, 0.06) 0.002 1.02 (0.72, 1.44) 0.929 n.s. Diet OLS (0) 0.37 (0.28, 0.48) < 0.001 0.19 (0.27, 0.12) < 0.001 1.05 (0.90, 1.23) 0.527 n.s. PGLS 0.709** 0.31 (0.21, 0.47) < 0.001 0.18 (0.29, 0.08) 0.001 1.18 (0.99, 1.41) 0.066 n.s. All carnivores (n = 31) OLS (0) 0.28 (0.19, 0.43) < 0.001 0.11 (0.24, 0.02) 0.112 ––– PGLS 1.000* 0.22 (0.12, 0.40) < 0.001 0.08 (0.23, 0.07) 0.290 ––– All herbivores (n = 95) OLS (0) 0.43 (0.30, 0.59) < 0.001 0.22 (0.31, 0.13) < 0.001 ––– PGLS 0.511** 0.39 (0.25, 0.59) < 0.001 0.22 (0.33, 0.10) < 0.001 ––– Synapsids (n = 86) OLS (0) 0.41 (0.29, 0.59) < 0.001 0.22 (0.32, 0.11) < 0.001 ––– PGLS 0.882** 0.19 (0.11, 0.33) < 0.001 0.17 (0.31, 0.02) 0.028 ––– Basal synapsid OLS (0) 0.43 (0.30, 0.61) < 0.001 0.22 (0.33, 0.12) < 0.001 0.83 (0.65, 1.06) 0.140 n.s. PGLS 0.796** 0.28 (0.11, 0.74) 0.012 0.21 (0.36, 0.06) 0.006 0.19 (0.04, 0.90) 0.040 0.031 Diet OLS (0) 0.41 (0.29, 0.59) < 0.001 0.22 (0.33, 0.11) < 0.001 1.02 (0.84, 1.22) 0.876 n.s. PGLS 0.826** 0.20 (0.12, 0.33) < 0.001 0.21 (0.35, 0.07) 0.005 1.33 (1.08, 1.64) 0.010 n.s. Basal synapsids (n = 10) OLS (0) 0.09 (0.01, 0.81) 0.064 0.22 (0.48, 0.91) 0.563 ––– PGLS 0*** 0.04 (0.00, 0.44) 0.031 0.46 (0.34, 1.26) 0.292 ––– Mammals (n = 76) OLS (0) 0.45 (0.31, 0.63) < 0.001 0.23 (0.34, 0.13) < 0.001 ––– PGLS 0.180 0.46 (0.31, 0.67) < 0.001 0.22 (0.33, 0.11) < 0.001 ––– Diet OLS (0) 0.46 (0.32, 0.65) < 0.001 0.23 (0.33, 0.12) < 0.001 0.93 (0.76, 1.14) 0.509 n.s. PGLS 0.171 0.47 (0.31, 0.70) < 0.001 0.22 (0.33, 0.10) < 0.001 0.96 (0.76, 1.22) 0.756 n.s. Mammal carnivores (n = 18) OLS (0) 0.31 (0.22, 0.43) < 0.001 0.09 (0.21, 0.03) 0.146 ––– PGLS 0.709*** 0.32 (0.22, 0.46) < 0.001 0.11 (0.23, 0.01) 0.084 ––– Mammal herbivores (n = 58) OLS (0) 0.48 (0.31, 0.77) 0.031 0.26 (0.40, 0.13) < 0.001 ––– PGLS 0.147 0.53 (0.32, 0.87) 0.015 0.26 (0.40, 0.12) 0.001 ––– Diapsids (n = 38) OLS (0) 0.31 (0.19, 0.50) < 0.001 0.14 (0.26, 0.02) 0.029 ––– PGLS 0.609** 0.30 (0.16, 0.54) < 0.001 0.17 (0.33, 0.02) 0.036 ––– Diet OLS (0) 0.28 (0.17, 0.47) < 0.001 0.16 (0.28, 0.04) 0.015 1.24 (0.91, 1.68) 0.186 n.s. PGLS 0.600** 0.29 (0.15, 0.58) 0.001 0.17 (0.33, 0.01) 0.039 1.03 (0.72, 1.48) 0.866 n.s. Diapsid carnivores (n = 8) OLS (0) 0.20 (0.11, 0.37) 0.002 0.06 (0.23, 0.11) 0.503 ––– PGLS 0.613*** 0.21 (0.11, 0.38) 0.003 0.08 (0.24, 0.08) 0.369 ––– Diapsid herbivores (n = 30) OLS (0) 0.41 (0.22, 0.77) 0.010 0.20 (0.35, 0.05) 0.015 ––– PGLS 0.633** 0.35 (0.16, 0.73) 0.010 0.20 (0.38, 0.01) 0.050 –––

Table 2. (continued)

† ‡ Stats k a (95% CI) Pb(95% CI) P Factor (95% CI) P Interaction P

Non-avian dinosaurs (n = 27) OLS (0) 1.57 (0.57, 4.34) 0.391 0.49 (0.72, 0.27) < 0.001 ––– PGLS 0.764* 0.39 (0.11, 1.39) 0.161 0.24 (0.53, 0.06) 0.127 ––– Diet OLS (0) 1.38 (0.47, 4.07) 0.562 0.49 (0.72, 0.26) < 0.001 1.15 (0.79, 1.67) 0.464 n.s. PGLS 0.766* 0.48 (0.11, 2.10) 0.338 0.25 (0.55, 0.05) 0.122 0.84 (0.43, 1.66) 0.621 n.s. Non-avian dinosaur herbivores (n = 23) OLS (0) 1.70 (0.57, 5.08) 0.355 0.51 (0.75, 0.26) 0.001 ––– PGLS 0.857* 0.44 (0.11, 1.79) 0.264 0.27 (0.60, 0.06) 0.122 ––– Chewer OLS (0) 1.92 (0.71, 5.18) 0.212 0.47 (0.69, 0.25) 0.001 0.68 (0.50, 0.93) 0.025 n.s. PGLS 0.713*** 0.93 (0.15, 5.70) 0.938 0.35 (0.69, 0.00) 0.063 0.64 (0.31, 1.30) 0.233 n.s.

Free-hull ratio represents the proportion of the convex hull reconstruction of the torso not immediately supported by bone; femur length in cm. *k significantly different from 0. **k significantly different from 0 and 1. ***k not significantly different from 0 and 1. † Factor coding: diet (carnivore = 0, herbivore = 1), synapsid/diapsid (diapsid = 0, synapsid = 1), basal synapsid (no basal synapsid = 0, basal synapsid = 1), chewer (chewer = 0, non-chewer = 1). ‡ Models were calculated with interaction term first; if this was not significant, the model was again calculated without the interaction term; estimates for the factor in this table always represent the models where either the interaction was significant or excluded. OLS, ordinary least squares; PGLS, phylogenetic generalized least squares.

optimization or ‘escalation’ (Vermeij, 1987, 2013) of the represent an additional argument against galloping in the body shape in the synapsid lineage. former group. Differences in the ‘free-hull ratio’ may also In developing evolutionary arms race scenarios, such as be related to the degree that the gut can accommodate between predators and prey, the effects of differences in increasing intake levels by distension without compromising body shape with their effect on the center of gravity (Bates digesta retention times (Clauss et al. 2007). et al. 2009b, 2016), differences in the weight of digestive Examples such as the proboscideans and the proboscis organ tissue (Schiek & Millar, 1985), and especially the monkey (Nasalis larvatus) in Fig. 2a emphasize a limitation effects of putative differences in the weight of digestive of the convex hull method that may arguably even lead to tract contents (Muller€ et al. 2013) should be considered, an underestimation of the real difference between herbi- which may lead to different non-muscle:muscle ratios in vores and carnivores: the part of the convex hull that is not predators and prey. In the context of changes within lin- supported by bony structures, and hence is estimated as a eages, such as changes in insular forms in the absence of relatively straight line, might in reality be a bulging abdom- predators, estimating body cavity dimensions from carefully inal wall. Whereas in carnivores, the rib cage may usually reconstructed mounted skeletons may provide additional represent the most ventral part of the torso contour, this evidence to understand constraints of vertebrate bauplan lowest point is typically not marked by the rib cage in herbi- evolution. vores, but is positioned posterior to it and marked by the In our dataset, diapsids and synapsids shared the charac- soft-tissue abdominal wall (Starck, 1982). The reconstruction teristic of an increasing divergence in the ‘free-hull ratio’ of this soft tissue border is particularly difﬁcult from with increasing body size. Some species had a high, and mounted skeletons (Bates et al. 2009b). In the proboscis some had a low proportion of the body cavity delineated monkey, with its typical bulging belly (Harding, 2015), it by soft tissue only. Such differences may be linked to differ- seemsevenasifareductionintheextentoftheribcage ences in cursoriality (Bramble, 1987), where a more rigid facilitates the extreme expansion of the abdominal cavity – torso (with a lower ‘free-hull ratio’) may be a prerequisite an effect not reﬂected in the convex hull estimate of the for galloping. For example, considering the debate about torso in this species. Correspondingly, in our dataset, the the locomotion capabilities of Triceratops (Thulborn, 1982; proboscis monkey represented an outlier as the mammalian Paul & Christiansen, 2000), the similarity of Triceratops to herbivore with the smallest relative torso volume (Fig. 2a). proboscideans (which do not gallop) with respect to an For a more realistic approximation of the total body cavity abdominal cavity with particularly little bony support might volumes, more comprehensive studies that include 3D

Fig. 3 Relationship between the femur length (as proxy for body size) and the proportion of the torso not supported by bone (free-hull ratio) in (a) synapsids and (b) diapsids. Closed symbols and full regression Fig. 2 Relationship between the femur length (as proxy for body size) lines (cf. Table 2) indicate herbivores (except for the Amphibia), open and the reconstructed volume of the body cavity in (a) synapsids and symbols and dotted lines indicate carnivores. Skeletal models with the (b) diapsids. Closed symbols and full regression lines (cf. Table 1) indi- estimated convex hull of the torso depicted include: (a, from top to cate herbivores (except for the Amphibia), open symbols and dotted bottom) Mammutus, Elephas, Giraffa, Diceros; (b, top to bottom) line indicate carnivores. Skeletal models with the estimated convex hull Triceratops, Atlasaurus, Diplodocus. Regression lines in (a) for mam- of the torso depicted include: (a, from left to right) Lycaenops, mals, in (b) for all diapsids. Moschops, Nasalis, Panthera leo, Bos gaurus; (b, from left to right) Varanus, Euoplocephalus, Giraffatitan, Stegosaurus, Iguanodon. Regression lines in (a) for mammals, in (b) for all diapsids. different lung anatomy between synapsids and diapsids, due to different levels of metabolism leading to differences reconstructions of taxidermic specimens or live animals at in the distinction in digestive anatomy between trophic various stages of food intake levels may be required. To guilds, or other hitherto unknown factors. our knowledge, no systematic investigations on these different bauplan strategies exist. In theory, animals could Acknowledgements evolve a voluminous body cavity either by soft tissue expansion, by a deepening and broadening of their ribc- The authors thank Najat Aquesbi and Mohammed Rochdy (Ministry age and corresponding pelvic structures, or by a combina- of Energy and Mines, Rabat), Thomas Bolliger (Sauriermuseum Aathal), Ken Carpenter (Utah State University Eastern Prehistoric tion of both. Museum), Loic Costeur (Natural History Museum Basle), Rainer Hut- In conclusion, differences in the body cavity volume that terer (Alexander Koenig Research Museum Bonn), Chen-sen Li (Bei- exist between herbivores and carnivores exist in mammals jing Museum of Natural History), Mark Norell and Carl Mehling that most likely reﬂect differences in the digestive anatomy (American Museum of Natural History), Barbara Oberholzer (Zoo- and physiology between these groups (Stevens & Hume, logical Museum, University of Zurich), Daniela Schwarz (Natural 1998). The apparent decrease in body cavity volume from History Museum Berlin), Paul Simoens and Marjan Doom (Depart- basal synapsids to mammals possibly represents an example ment of Morphology, Ghent University), Ingmar Werneburg (University of Tubingen),€ and Ye Yong and Peng Guangzhao of evolutionary optimization. In the comparison of dino- (Zigong Dinosaur Museum). Lucas Walstijn and Lida Fanara helped saurs with mammals, in addition to questions about the reli- with digital processing. The authors thank two reviewers for ability of skeletal reconstructions, our preliminary ﬁndings insightful comments that improved the manuscript. MC thanks may hint at fundamental bauplan differences linked to the Deborah Sarah Peter for inspiring this work. This study was

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R Foundation for Statistical Computing, Vienna, and digestive tract specialization: examples from the lizard Austria ISBN 3-900051-07-0, URL http://wwwR-projectorg/. family Liolaemidae. Zoology 108, 201–210. Thulborn RA (1982) Speeds and gaits of dinosaurs. Palaeogeogr Orme D, Freckleton R, Thomas G, et al. (2010) Caper: compara- Palaeoclimatol Palaeoecol 38, 227–256. tive analyses of phylogenetics and evolution in R. R package Treves F (1886) Abstracts of six lectures on the intestinal canal version 04/r71 See http://caperr-forger-projectorg/. and peritoneum in the mammalia. Br Med J i, 583–584, 638– Orr RT (1976) Vertebrate Biology. Philadelphia: WB Saunders. 640. Pagel M (1999) Inferring the historical patterns of biological Vermeij GJ (1987) Evolution and Escalation: an Ecological History evolution. Nature 401, 877–884. of Life. Princeton, NJ: Princeton University Press. Paul GS, Christiansen P (2000) Forelimb posture in neoceratop- Vermeij GJ (2013) On escalation. Annu Rev Earth Planet Sci 41, sian dinosaurs: implications for gait and locomotion. Paleobi- 1–19. ology 26, 450–465. Wagner CE, McIntyre PB, Buels KS, et al. (2009) Diet predicts Perry SF, Breuer T, Pajor N (2011) Structure and function of the intestine length in Lake Tanganyika’s cichlid fishes. Funct Ecol sauropod respiratory system. In: Understanding the Life of 23, 1122–1131. Giants the Biology of the Sauropod Dinosaurs. (eds Klein N, Walls GY (1981) Feeding ecology of the tuatara (Sphenodon Remes K, Gee CT, Sander M), pp. 83–93. Bloomington: Indiana punctatus) on Stephens Island, Cook Strait. N Z J Ecol 4,89–97. University Press. Wang DH, Pei YX, Yang JC, et al. (2003) Digestive tract mor- Peters RH (1983) The Ecological Implications of Body Size. Cam- phology and food habits in six species of rodents. Folia Zool bridge: Cambridge University Press. 52,51–56. Pinheiro J, Bates D, DebRoy S, et al. R Development Core Team Weishampel DB, Dodson P, Osmolska A (1990) The Dinosauria. (2011) Nlme: linear and nonlinear mixed effects models. R Berkeley: University of California Press. package version 3 1–102 Available at https://cranr-projectorg/ Werner J, Griebeler EM (2014) Allometries of maximum growth web/packages/nlme/. rate versus body mass at maximum growth indicate that non- Potgieter KR, Davies-Mostert HT (2012) A simple visual estima- avian dinosaurs had growth rates typical of fast growing tion of food consumption in carnivores. PLoS One 7, e34543. ectothermic sauropsids. PLoS One 9, e88834. Rand AS, Dugan BA, Monteza H, et al. (1990) The diet of a gen- Wilman H, Belmaker J, Simpson J, et al. (2014) Elton traits 1.0: eralized folivore: Iguana iguana in Panama. J Herpetol 24, species-level foraging attributes of the world’s birds and 211–214. mammals. Ecology, 95, 2027.

Wings O, Sander PM (2007) No gastric mill in sauropod dino- Fig. S4. 3D skeleton reconstructions of non-avian dinosaurs (in- saurs: new evidence from analysis of gastrolith mass and func- cluding indications of the convex hull of the body cavity). tion in ostriches. Proc R Soc B 274, 635–640. Fig. S5. 3D skeleton reconstructions of reptiles and amphibia (in- Wu C (2007) SiftGPU: a GPU implementation of scale invariant cluding indications of the convex hull of the body cavity). feature transform (SIFT). Available at: http://cs.unc.edu/ Fig. S6. Phylogenetic tree (also available as supplementary nexus ccwu/siftgpu. ﬁle). Wu C (2012) VisualSFM: a Visual Structure from Motion System. Fig. S7. Visual outlier inspection: exclusion of the ﬂamingo Available at http://www.cs.washington.edu/home/ccwu/vsfm. (combination of very long femur and very small torso) and two Wu C, Agarwal S, Curless B, et al. (2011) Multicore bundle marine mammals (combination of very short femurs and very adjustment. Proc Conf Comput Vis Pattern Recognit 24, 3057– voluminous torsos). 3064. Table S1. Specimens used in this study, categories and measurements. Table S2. Time of divergence provided for different nodes in Supporting Information the tree. Table S3. Results of statistical analyses according to Torso vol- Additional Supporting Information may be found in the online ume = a (factor) Body massb (and the corresponding fac- version of this article: tor 9 body mass interaction) in OLS and PGLS for extant Fig. S1. 3D skeleton reconstructions of early synapsids (including mammals, birds and reptiles (n = 63). indications of the convex hull of the body cavity). Table S4. Results of statistical analyses according to Body Fig. S2. 3D skeleton reconstructions of mammals (including indi- mass = a (factor) Femur lengthb (and the corresponding fac- cations of the convex hull of the body cavity). tor 9 femur length interaction) in OLS and PGLS for extant Fig. S3. 3D skeleton reconstructions of birds (including indica- mammals, birds and reptiles (n = 63). tions of the convex hull of the body cavity).

Journal of Anatomy - Evolutionary Morphology Online Supplement for

Body cavity volume reconstruction in terrestrial tetrapods

Marcus Clauss, Irina Nurutdinova, Carlo Meloro, Hanns-Christian Gunga, Duofang Jiang, Johannes Koller, Bernd Herkner, P. Martin Sander, Olaf Hellwich

Correspondence [email protected]

Supplement: Tetrapod body cavities 2

Basal synapsids/ mammal-like reptiles

Chiniquodon Dimetrodon Edaphosaurus Keratocephalus

Lycaenops Moschops Ophiacodon Sauroctonus

Stahleckeria Tetragonias

Figure S1. 3D skeleton reconstructions of early synapsids (incl. indications of the convex hull of the body cavity).

Supplement: Tetrapod body cavities 3

Mammals

Acinonyx Agouti Ailurus Amphicyon

Archaeotherium Arctitis Bison* Blastocerus

Bos gaurus Bos taurus* Brontops Camelus

Canis Caracal Castor Cavia

Cephalophus Cervus* Choloepus Dama

Dicerorhinus* Diceros Dinohippus Elephantulus

Elephas Equus caballus* Equus scotti Felis

Gazella Giraffa Glossotherium Gomphotherium Supplement: Tetrapod body cavities 4

Gorilla Herpestes Hexaprotodon Hippopotamus

Hoplophoenus Hyaenodon Hydrochaeris Hystrix

Indricotherium# Lama Lemmus Loxodonta*

Lutra Mammut Mammuthus Megaladapis

Megaloceros* Merychippus Metaxytherium Myrmecophaga

Nasalis Neohipparion Okapia Palaeoparadoxia

Panthera leo Panthera pardus Panthera tigris Pecari

Phascolarctos Phascolonus Platygonus Procavia Supplement: Tetrapod body cavities 5

Rangifer* Smilodon Sus* Tamandua

Tapirus indicus* Tapirus terrestris Toxodon Tragulus

Ursus maritimus* Ursus spelaeus Vombatus Vulpes

Wallabia Zalophus

Figure S2. 3D skeleton reconstructions of mammals (incl. indications of the convex hull of the body cavity). Reconstructions from this study, except *(from Sellers et al., 2012) and #(from Stoinski et al., 2011).

Supplement: Tetrapod body cavities 6

Birds

Anser Apteryx Grus Phoenicopterus

Rhea Sagittarius Struthio

Figure S3. 3D skeleton reconstructions of birds (incl. indications of the convex hull of the body cavity).

Supplement: Tetrapod body cavities 7

Non-avian dinosaurs

Allosaurus* Atlasaurus* Bactrosaurus* Datousaurus*

Diplodocus carnegii* Diplodocus longus Edmontosaurus Euoplocephalus

Gastonia Gigantspinosaurus* Giraffatitan§ Iguanodon

Mamenchisaurus Mamenchisaurus Lufengosaurus* constructus* jingyanensis* Omeisaurus*

Plateosaurus# Protoceratops* Shunosaurus* Stegosaurus*

Stegosaurus stenops Szechuanosaurus* Tenontosaurus Triceratops

Tyrannosaurus Yandusaurus* Yangchuanosaurus*

Figure S4. 3D skeleton reconstructions of non-avian dinosaurs (incl. indications of the convex hull of the body cavity). Reconstructions from this study, except #(from Gunga et al., 2007), §(from Gunga et al., 2008), *(from Stoinski et al., 2011).

Supplement: Tetrapod body cavities 8

Reptiles

Iguana Sphenodon

Stenaulorhynchus Trilophosaurus

Varanus

Amphibia

Diadectes Eryops

Figure S5. 3D skeleton reconstructions of reptiles and amphibia (incl. indications of the convex hull of the body cavity).

Table S1. Specimens used in this study, categories and measurements Femur Torso Free-hull Mirrored/ ID Specimen as taken Species name in tree Fooda Chewb Originc Sourced length volume ratio split torso at Origin cm cm3

Early synapsids Chiniquodon theotonicus Chiniquodon theotonicus carn 16.45 25257.3 0.235 mirr GPIT 1 RE-07112 (Belesodon magnificus) Dimetrodon incisivus Dimetrodon incisivus carn 17.99 52310.0 0.084 - GPIT 1 RE-07100 Edaphosaurus boanerges Edaphosaurus boanerges herb 18.54 38933.1 0.129 - AMNH 1 7003 Keratocephalus moloch Keratocephalus moloch herb 32.31 591338.0 0.299 mirr GPIT 1 RE-07102 Lycaenops ornatus Lycaenops ornatus carn 18.18 10442.8 0.199 - AMNH 1 2240 Moschops capensis Moschops capensis herb 38.28 445972.0 0.167 - AMNH 1 5552 Ophiacodon retroversus Ophiacodon retroversus carn 17.90 32421.0 0.127 mirr AMNH 1 4155 Sauroctonus parringtoni Sauroctonus parringtoni carn 18.65 18277.5 0.207 - GPIT 1 RE-07113 Stahleckeria potens Stahleckeria potens herb 45.02 867003.0 0.172 - GPIT 1 RE-07106 Tetragonias (Dicynodon) njalilus Tetragonias njalilus herb 20.46 67309.0 0.258 - GPIT 1 RE-08649 Mammals Acinonyx jubatus Acinonyx jubatus carn 23.23 5913.2 0.252 - ZFMK 1 MAM 1931.0070 Coelogenys paca Agouti paca herb 10.22 2212.2 0.307 - ZMUZ 1 10698 Ailurus fulgens Ailurus fulgens herb 10.93 1457.1 0.203 mirr BNHM 1 8223 Amphicyon ingens Amphicyon ingens carn 53.85 167553.0 0.220 - AMNH 1 FAM 68117/54262 Archaeotherium mortoni Archaeotherium mortoni herb 28.58 58047.3 0.254 - AMNH 1 11323 Arctictis binturong Arctictis binturong herb 15.59 4726.7 0.337 - BNHM 1 7553 Bison bison Bison bison herb 42.42 275565.0 0.093 - 2

Blastoceros pampaeus Blastocerus dichotomus herb 22.96 16767.9 0.237 - AMNH 1 11202 Bos gaurus Bos frontalis herb 56.48 545800.0 0.243 - AMNH 1 18465 Bos taurus Bos taurus herb 37.37 145353.0 0.214 - 2

Brontops robustus Brontops robustus herb 80.50 1569812.0 0.138 - AMNH 1 518 Camelus dromedarius Camelus dromedarius herb 54.66 284066.0 0.163 - DMUG 1 no ID Canis canis Canis lupus carn 26.45 22138.5 0.193 split DMUG 1 no ID Caracal caracal Caracal caracal carn 17.13 2708.5 0.323 split BNHM 1 10766 Castor canadensis Castor canadensis herb 11.40 5654.2 0.250 - BNHM 1 1997 (ctd.) Supplement: Tetrapod body cavities 10

Femur Torso Free-hull Mirrored/ ID Specimen as taken Species name in tree Fooda Chewb Originc Sourced length volume ratio split torso at Origin cm cm3

Cavia porcellus Cavia porcellus herb 4.66 354.5 0.360 - CZAEPW 1 no ID Cephalophus niger Cephalophus niger herb 18.00 9507.9 0.244 - BNHM 1 2493 Cervus elaphus Cervus elaphus herb 29.12 53778.3 0.196 - 2

Choloepus didactylus Choloepus didactylus herb 16.87 5262.1 0.267 split ZFMK 1 no ID Dama dama Dama dama herb 21.17 21706.5 0.250 - DMUG 1 no ID Dicerorhinus sumatrensis Dicerorhinus sumatrensis herb 40.91 251521.0 0.073 - 2

Diceros bicornis Diceros bicornis herb 43.14 364154.0 0.054 - ZFMK 1 MAM 1934.0047 Dinohippus leidyanus Dinohippus leidyanus herb 33.51 73237.2 0.224 - AMNH 1 17224 Elephantulus rozeti Elephantulus rozeti carn 2.41 14.7 0.285 - BNHM 1 9159 Elephas maximus Elephas maximus herb 93.09 1323760.0 0.193 - DMUG 1 no ID Equus caballus Equus caballus herb 51.65 233771.0 0.114 - 2

Equus scotti Equus scotti herb 41.07 209734.0 0.196 - AMNH 1 10606 Felis catus Felis silvestris carn 12.64 1713.9 0.271 - ZFMK 1 MAM 1986.0005 Nanger dama Gazella dama herb 24.89 24901.2 0.174 - BNHM 1 1467 Giraffa camelopardalis Giraffa camelopardalis herb 49.87 295159.4 0.061 - DMUG 1 no ID Glossotherium robustus Glossotherium robustus herb 47.08 483877.0 0.139 - AMNH 1 11277 Gomphotherium productum Gomphotherium productum herb 66.58 2739370.0 0.238 - AMNH 1 10582 Gorilla gorilla Gorilla gorilla herb 38.25 43739.2 0.106 - ZMUZ 1 11880 Herpestes brachyurus Herpestes brachyurus carn 7.28 676.7 0.269 - ZMUZ 1 10328 Hexaprotodon liberiensis Hexaprotodon liberiensis herb 24.77 53075.2 0.180 - DMUG 1 no ID Hippopotamus amphibius Hippopotamus amphibius herb 48.91 475857.0 0.192 - BNHM 1 2767 Hoplophoneus primaevus Hoplophoneus primaevus carn 21.35 9944.9 0.337 - AMNH 1 1406 Hyaenodon horridus Hyaenodon horridus carn 21.92 12888.4 0.279 - AMNH 1 1375 Hydrochaeris hydrochaeris Hydrochaeris hydrochaeris herb 19.87 23589.2 0.329 split DMUG 1 no ID Hystrix spp. Hystrix cristata herb 12.02 6234.3 0.273 - DMUG 1 no ID Paracerathrium tianshanensis Indricotherium transouralicum herb 124.63 4969740.0 0.259 - BCNHM 3 no ID Lama guanicoe Lama guanicoe herb 32.48 71884.6 0.230 - ZMUZ 1 10814 Lemmus lemmus Lemmus lemmus herb 2.22 25.9 0.393 - CZAEPW 1 no ID Loxodonta africana Loxodonta africana herb 114.99 1546200.0 0.155 - 2

(ctd.) Supplement: Tetrapod body cavities 11

Femur Torso Free-hull Mirrored/ ID Specimen as taken Species name in tree Fooda Chewb Originc Sourced length volume ratio split torso at Origin cm cm3

Lutra lutra Lutra lutra carn 8.18 1841.2 0.198 split BNHM 1 115 Mammut americanum Mammut americanum herb 110.36 3563910.0 0.285 - AMNH 1 9951 Mammuthus jeffersoni Mammuthus columbi herb 127.38 2541860.0 0.213 - AMNH 1 FAM 99927 Megaladapis edwardsi Megaladapis edwardsi herb 23.33 42604.3 0.258 - AMNH 1 15868 Megaloceros giganteus Megaloceros giganteus herb 48.07 156848.0 0.229 - 2

Merychippus quintus Merychippus quintus herb 28.14 38294.0 0.232 - AMNH 1 14185 Metaxytherium floridanum Metaxytherium floridanum herb 17.20 279265.0 0.273 - AMNH 1 26838 Myrmecophaga tridactyla Myrmecophaga tridactyla carn 22.46 10049.6 0.160 - ZZ 1 no ID Nasalis larvatus Nasalis larvatus herb 22.27 3223.0 0.305 - ZFMK 1 MAM 1939.0042 Neohipparion affine Neohipparion affine herb 30.79 66395.5 0.268 - AMNH 1 9815 Okapia johnstoni Okapia johnstoni herb 34.36 111079.0 0.099 - BNHM 1 3940 Palaeoparadoxia tabatai Palaeoparadoxia tabatai herb 41.96 271982.0 0.240 - AMNH 1 129177 Panthera leo Panthera leo carn 30.97 31630.9 0.249 - DMUG 1 no ID Panthera pardus Panthera pardus carn 25.07 14958.9 0.212 - BNHM 1 273 Panthera tigris Panthera tigris carn 36.84 46061.8 0.208 - DMUG 1 no ID Pecari tajacu Pecari tajacu herb 17.68 12891.4 0.202 - BNHM 1 1071 Phascolarctos cinereus Phascolarctos cinereus herb 12.96 2781.3 0.327 - BNHM 1 6260 Phascolonus gigas Phascolonus gigas herb 33.80 168794.0 0.317 - AMNH 1 129499 Platygonus leptorhinus Platygonus compressus herb 21.15 25493.9 0.207 - AMNH 1 10388 Procavia capensis Procavia capensis herb 7.65 1488.4 0.356 - ZMUZ 1 10850 Rangifer tarandus Rangifer tarandus herb 30.90 50442.0 0.100 - 2

Smilodon floridanus Smilodon fatalis carn 39.34 59137.8 0.219 - AMNH 1 FM 14398 Sus scrofa Sus scrofa herb 24.58 45418.0 0.180 - 2

Tamandua mexicana Tamandua mexicana carn 7.70 865.3 0.245 - BNHM 1 1257 Tapirus indicus Tapirus indicus herb 35.26 103340.0 0.149 - 2

Tapirus terrestris Tapirus terrestris herb 29.90 50212.0 0.134 - ZFMK 1 MAM 1934.0105 Toxodon burmeisteri Toxodon platensis herb 60.97 762687.0 0.143 - AMNH 1 14943 Tragulus javanicus Tragulus javanicus herb 6.98 412.4 0.336 - ZMUZ 1 11021 Ursus maritimus Ursus maritimus carn 41.98 72996.4 0.188 - 2

(ctd.) Supplement: Tetrapod body cavities 12

Femur Torso Free-hull Mirrored/ ID Specimen as taken Species name in tree Fooda Chewb Originc Sourced length volume ratio split torso at Origin cm cm3

Ursus spelaeus Ursus spelaeus herb 45.71 161547.0 0.128 - AMNH 1 39416 Vombatus ursinus Vombatus ursinus herb 13.74 6447.2 0.215 - ZMUZ 1 11068 Vulpes vulpes Vulpes vulpes carn 14.16 2358.6 0.220 - ZFMK 1 MAM 1933.0126a Wallabia spp. Wallabia bicolor herb 17.00 5361.8 0.337 split DMUG 1 no ID Otarid spp. Zalophus californianus carn 7.26 9898.8 0.148 - DMUG 1 no ID Birds Anser anser Anser anser herb 8.12 2626.3 0.127 - DMUG 1 no ID Apteryx owenii Apteryx owenii herb 8.61 396.9 0.230 - BNHM 1 2344 Grus spp. Grus grus herb 16.23 4196.7 0.250 - DMUG 1 no ID Phoenicopterus roseus Phoenicopterus roseus carn 27.13 1194.0 0.229 - DMUG 1 no ID Rhea americana Rhea americana herb 20.53 12239.3 0.229 - DMUG 1 no ID Sagittarius serpentarius Sagittarius serpentarius carn 11.86 1334.9 0.206 - DMUG 1 no ID Struthio camelus Struthio camelus herb 32.22 73816.9 0.242 - DMUG 1 no ID Non-avian dinosaurs Allosaurus fragilis Allosaurus fragilis carn 84.28 774160.0 0.169 - SMA 3 Big Al II

Atlasaurus imelakei Atlasaurus imelakei herb nonchew 190.62 6535910.0 0.126 split MMEM 3 no ID Bactrosaurus johnsoni Bactrosaurus johnsoni herb chew 81.00 505908.0 0.232 - BCNHM 3 no ID Datousaurus bashanensis Datousaurus bashanensis herb nonchew 119.86 2829100.0 0.143 - ZMNH 3 no ID Diplodocus carnegii Diplodocus carnegii herb nonchew 158.01 6693450.0 0.083 - MNHB 3 no ID Diplodocus longus Diplodocus longus herb nonchew 144.33 3933920.0 0.127 - NMSF 1 no ID Anatotitan copei Edmontosaurus annectens herb chew 118.17 1499110.0 0.201 - AMNH 1 5886 Euoplocephalus tutus Euoplocephalus tutus herb nonchew 66.54 1873940.0 0.261 - NMSF 1 no ID Gastonia burgei Gastonia burgei herb nonchew 35.91 301690.0 0.280 - USUEPM 1 no ID Gigantspinosaurus sichuanensis Gigantspinosaurus sichuanensis herb nonchew 67.36 775033.0 0.281 - ZMNH 3 no ID Brachiosaurus brancai Giraffatitan brancai herb nonchew 197.46 17029000.0 0.101 - MNHB 5 no ID Iguanodon bernissartensis Iguanodon bernissartensis herb chew 102.17 2242310.0 0.185 - NMSF 1 no ID Lufengosaurus huenei Lufengosaurus huenei herb nonchew 56.38 339974.0 0.157 - BCNHM 3 no ID Mamenchisaurus constructus Mamenchisaurus constructus herb nonchew 146.74 5709280.0 0.194 - ZMNH 3 no ID Mamenchisaurus jingyanensis Mamenchisaurus jingyanensis herb nonchew 142.95 6206260.0 0.163 - BCNHM 3 no ID (ctd.) Supplement: Tetrapod body cavities 13

Femur Torso Free-hull Mirrored/ ID Specimen as taken Species name in tree Fooda Chewb Originc Sourced length volume ratio split torso at Origin cm cm3

Omeisaurus yianfuensis Omeisaurus yianfuensis herb nonchew 129.40 5695660.0 0.065 - ZMNH 3 no ID Plateosaurus engelhardti Plateosaurus engelhardti herb nonchew 58.03 322912.0 0.102 - GPIT 4 RE-07288 Protoceratops andrewsi Protoceratops andrewsi herb chew 24.61 28244.8 0.456 - BCNHM 3 no ID Shunosaurus lii Shunosaurus lii herb nonchew 90.41 1730150.0 0.106 - ZMNH 3 no ID Stegosaurus Stegosaurus armatus herb nonchew 78.47 802276.0 0.236 mirr SMA 3 Moritz Stegosaurus stenops Stegosaurus stenops herb nonchew 107.66 1425560.0 0.213 - NMSF 1 no ID Szechuanosaurus campi Szechuanosaurus campi carn 60.20 269308.0 0.143 - ZMNH 3 no ID

Tenontosaurus tilletti Tenontosaurus tilletti herb chew 71.65 411004.0 0.282 - AMNH 1 FARB 3034 Triceratops elatus Triceratops horridus herb chew 104.74 3113700.0 0.239 - NMSF 1 no ID Tyrannosaurus rex Tyrannosaurus rex carn 126.47 3762000.0 0.134 - NMSF 1 no ID

Yandusaurus multidens Yandusaurus hongheensis herb nonchew 15.80 4213.4 0.325 - ZMNH 3 no ID Yangchuanosaurus hepingensis Yangchuanosaurus shangyouensis carn 98.57 974264.0 0.167 - ZMNH 3 no ID

Reptiles Iguana rhinolopha Iguana iguana herb 9.01 1012.1 0.271 - BNHM 1 1260 Sphenodon punctatus Sphenodon punctatus carn 4.42 163.8 0.183 split ZMUZ 1 no ID Stenaulorhynchus stockley Stenaulorhynchus stockley herb 17.71 33364.7 0.197 - GPIT 1 RE-07192 Trilophosaurus buettneri Trilophosaurus buettneri herb 23.88 11695.5 0.151 - AMNH 1 7502 Varanus salvator Varanus salvator carn 13.18 13188.5 0.105 - ZMUZ 1 no ID Amphibia Diadectes phaseolinus Diadectes phaseolinus herb 18.75 72289.2 0.231 - AMNH 1 4684 Eryops megacephalus Eryops megacephalus carn 19.46 32237.5 0.324 - AMNH 1 4657 abased on Walls (1981), Losos and Greene (1988), Rand et al. (1990), Weishampel et al. (1990), Reisz and Sues (2000), Reisz (2006), Wilman et al. (2014) and the Paleobiology Database (www.paleobiodb.org) bbased on Weishampel et al. (1990) and Wings and Sander (2007) cfor skeletons from sources 1, 3-5: AMNH American Museum of Natural History New York USA, BCNHM = Bejing Natural History Museum China, BNHM = Natural History Museum Basle Switzerland, CZAEPW = Clinic of Zoo Animals Exotic Pets and Wildlife Univeristy of Zurich Switzerland, DMUG = Anatomy Museum Department of Morphology Faculty of Veterinary Medicine Ghent University Belgium, MMEM = Moroccan Ministry of Energy and Mining Morocco, MNHB = Natural History Museum Berlin Germany, NMSF = Senckenberg Naturmuseum Frankfurt Germany, GPIT = Paleontological Collection University of Tübingen Germany, SMA = Sauriermuseum Aathal Switzerland, USUEPM = Utah State University Eastern Prehistoric Museum Price USA, ZFMK = Alexander Koenig Research Museum Bonn Germany, ZMNH = Zigong Museum of Natural History China, ZMUZ = Zoological Museum University of Zurich Switzerland, ZZ = Zurich Zoo Switzerland dSources: 1 = this study, 2 = Sellers et al. (2012), 3 = described in Stoinski et al. (2011), 4 = described in Gunga et al. (2007), 5 = described in Gunga et al. (2008)

Supplement: Tetrapod body cavities 1

Phylogenetic tree The phylogenetic tree (Fig. S6) used in the PGLS analysis was constructed based on various sources. The topology was based on a combination of tree sources that included some of the most recent phylogenetic hypotheses. Due to the taxa selection of the present study, which was mainly driven by mounted skeleton availability and the logistics of obtaining their respective scans or photographs, it was not possible to build a supertree based on a character matrix because the taxa considered were too distantly related. Due to the sample, inevitably certain taxonomic groups (i.e., mammals) are more represented than others. The phylogeny includes both fossil and living tetrapods. The basic topology of tetrapod groups is based on tree of life project (Maddison and Schulz, 2007) supplemented with specific references. Eryops megacephalus is here basal to all the other taxa as member of Temnospondyli (extinct group of primitive tetrapods) (Ruta et al., 2007). It is followed by Diadectes phaseolinus, the sister taxon of all the Amniota (Berman and Henrici, 2003). Within the Amniota an early split is recognised between the Diapsida and the Synapsida (represented by basal Eupleycosauria, therapsids, and mammals) (Benton, 2014). Within Diapsida, the sample is characterized by a mix of extant and fossil Sauria. The presence of extant Sphenodon, Iguana and Varanus characterizes the split of Lepidosauriamorpha from Archosauriamorpha that include crocodiles (not present in our study), birds and their fossil relatives (i.e., dinosaurs). The position of Sphenodon relative to the other Squamata follows Pyron et al. (Pyron et al., 2013). Within Archosauromorpha we positioned Trilophosaurus and Stenaulorhynchus basal to dinosaurs and birds after Ezcurra et al. (Ezcurra et al., 2014) who presented a recent updated phylogeny of Sauria. In their topology Stenaulorhynchus is not present however Trilophosaurus is positioned basal to Rhynchosauria (the group to which Stenaulorhynchus belongs). Dinosauria is the other large clade of Archosauromorpha. Its topology is based on the supertree of Lloyd et al. (Lloyd et al., 2008) with the manual addition of extant Aves as from the topology in Xu et al. (Xu et al., 2014). The position of certain specific dinosaur taxa was updated such as that of Datousaurus bashanensis that is basal to Eusaropoda (Sekiya, 2011) and for Szechuanosaurus campi that is closely related to Yangchuanosaurus within theropods (Carrano et al., 2012). Modern bird topology was generated after Jetz et al. (Jetz et al., 2012), and Prum et al. (Prum et al., 2015) with respect to the position of the kiwi (Apteryx owenii) and the rhea (Rhea americana). Within Synapsida, the position of primitive Eupelycosauria and the general topology of therapsids follows Sidor (Sidor, 2003). The historical Beselodon magnificus was updated as Chiniquodon theotonicus (member of Eucynodontia) (Abdala and Giannini, 2002), and Scymnognathus parringtoni was named Sauroctonus parringtoni (Gebauer, 2014). For mammals the topology of extant taxa was generated following Bininda-Emonds et al. (Bininda-Emonds et al., 2007, Bininda-Emonds et al., 2008) with the addition of specific fossil branches after Raia et al. (Raia et al., 2013). A substantial addition was the inclusion of the fossil Notoungulate Toxodon and the Demostylia Palaeoparadoxia, whose taxonomic position was recently updated as basal members of Perissodactyla (Cooper et al., 2014, Welker et al., 2015). Following Cooper et al. (Cooper et al., 2014) for Palaeoparadoxia also allowed to place the ancient sirenid Metaxytherium as sister Supplement: Tetrapod body cavities 2 taxon of Proboscidea. For fossil Xenathra we followed the topology presented by Gaudin (Gaudin, 2004). The position of Ferae (Carnivora and Creodonta) and basal ungulates follows Raia et al. (Raia et al., 2013) and Spaulding et al. (Spaulding et al., 2009) while the relationship of primates and extant rodents follows Bininda-Emonds et al. (Bininda- Emonds et al., 2007, Bininda-Emonds et al., 2008). In order to date the tree we opted to combine multiple empirical and analytical approaches. Firstly we recorded first and last occurrence for each taxon with the assumption that last occurrence for all extant species is zero. To avoid bias in relation to the scattered information, we employed the palaeodb website (http://fossilworks.org/?page=paleodb) to record species' time ranges. When a particular species was not present in the database, we used the genus range or conservatively stratigraphic clues based on the literature. We then employed the script 'timePaleoPhy' from the R package 'paleotree' (Bapst, 2013) to constrain time of divergence of taxa based on their stratigraphic occurrences. This script follows the same method proposed by Brusatte et al. (Brusatte et al., 2008) to date the supertree of fossil dinosaurs. In addition, we constrained the tree internal nodes based on Kepska et al. (Ksepka et al., 2015). The list of nodes and their respective dates (Table S2) was compiled after searching the fossil calibration database that includes some but not all of the internal nodes for our topology.

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Table S2. Time of divergence provided for different nodes in the tree. Dates are conservatively based on the maximum nodal age reported on the website http://fossilcalibrations.org/ developed by Ksepka et al. (Ksepka et al., 2015). All the other internal nodes ages were set to 'NA' and automatically generated using the script timepaleophy (Bapst, 2013). Node # Node label Time 1 Tetrapoda 351 3 Amniota 332.9 11 Theria 169.6 14 Boreoeutheria 164.6 15 Euarchontoglires 164.6 16 Rodentia 66 19 Primates 66 25 Whippomorpha 66 29 Bovidae 28.1 56 Carnivora 66 73 Xenarthra 164.6 76 Afrotheria 164.6 78 Sirenia 66 79 Proboscidea 23.03 83 Marsupialia 131.3 89 Diapsida 295.9 90 Archosauromorpha 255.9 92 Dinosauria 235 93 Ornitischia 230 105 Sauropodomorpha 232 120 Palaeognathae 86.8 122 Neognathae 86.8 123 Neoaves 60.2 125 Lepidosauria 252.7 126 Squamata 209.5

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Figure S6. Phylogenetic tree (also available as supplementary nexus file)

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Outliers Three outliers were eliminated from the dataset used in the main study after visual inspection: the flamingo (Phoenicopterus), the sirenian (Metaxytherium) and the sea lion (Zalopus) (Fig. S7). In the case of the flamingos, we can only speculate that its typical diet - shrimp and algae caught in the filter system of the beak (Zweers et al., 1995) - is so small and requires so little processing that a particularly small gastrointestinal tract and coelomic cavity is feasible, and/or that flamingos have particularly long legs for their body volume. In the case of the marine mammals, it is plausible that the different mechanical constraints of their lifestyle leads to systematically different proportions of limbs and torso (Jones and Pierce, 2016).

10$

1$ Metaxytherium- )$ 3 0.1$ Zalophus- 0.01$

Torso$volume$(m 0.001$ Phoenicopterus- 0.0001$

0.00001$ 2$ 20$ 200$ Femur$length$(cm)$

Figure S7. Visual outlier inspection: exclusion of the flamingo (combination of very long femur and very small torso) and two marine mammals (combination of very short femurs and very voluminous torsos)

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Considerations about body mass in relation to torso volume While the necessity to control for body size is self-evident, the answer to the question about which proxy is most suitable is not. Body mass is the most common basis against which other morphological and physiological measures are compared (Peters, 1983, Calder, 1996, Sibly et al., 2012). However, the volume of the torso represents a major proportion of overall body mass. Therefore, differences in torso volume most certainly are reflected in body mass differences already. On the other hand, we could hence predict that we could use body mass itself as a proxy for 'torso volume', and the relationship of body mass to femur length should resemble that of torso volume to femur length. For the testing of these hypotheses, a valid dataset is required where all measurements are taken from the same, healthy individuals. In particular, when using body mass in this way, the feeding status of the animals used for the measurement is critical. To our knowledge, the largest dataset on femur length and body mass is presented by Campione and Evans (2012); however, the methods do not indicate a protocol about the feeding status, i.e. the degree of gut fill, in the animals. In particular in herbivores, gut fill represents a constant, relevant proportion of body mass (Clauss et al., 2013) that is considered the reason for their larger torso volumes. Using the elephant as an example, Clauss et al. (2005) demonstrated how the feeding status of animals whose body mass and gut fill are measured can influence the position of a species in comparative datasets. To date, most likely, no completely reliable large data collection on body mass and femur length exists. However, it is noteworthy that in the data evaluated by Campione and Evans (2012), there is a difference in the femur length-body mass relationship between Carnivora (i.e., mainly carnivores) and Ungulata (i.e., mainly herbivores) that could indicate that, at comparable femur length, Ungulata have higher body masses than Carnivora - a finding that would corroborate the prediction made above. Campione and Evans (2012) demonstrate that femur circumference is better related to body mass than femur length; for the question of our study this means that femur circumference would probably be a less suitable proxy as it equalizes differences in body mass at similar stature. To perform an explorative test of these considerations, we compiled body mass data for the extant mammals, birds and reptiles of our dataset from a single source - the Animal Diversity Web (www.animaldiversity.org, accessed 25.05.2016). We consistently collected the mean (or calculated it from the minimum and maximum provided), even if in some cases the data given did not appear intuitively correct, added it to our own dataset (Table S1), and performed analyses using the same methods as outlined in the main text. There was a linear relationship (scaling including the exponent of 1.0 in the 95%CI) between torso volume and body mass, with no influence of diet (Table S3). In contrast, there was an expected cubic scaling for the relationship of body mass and femur length, and diet was a significant factor, suggesting that for similar femur lengths, herbivores have higher body masses than carnivores (Table S4).

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Table S3. Results of statistical analyses according to Torso volume = a (factor) Body massb (and the corresponding factor*Body mass interaction) in Ordinary Least Squares (OLS) and Phylogenetic Generalized Least Squares (PGLS) for extant mammals, birds and reptiles (n=63) Stats λ a b factor# interaction† (95%CI) p (95%CI) p (95%CI) p p Diet OLS (0) 384 <0.001 0.94 <0.001 1.07 0.680 n.s. (286, 515) (0.88, 1.00) (0.77, 1.48) PGLS 0 384 <0.001 0.94 <0.001 1.07 0.681 n.s. (286, 515) (0.88, 1.00) (0.77, 1.48) this is only an explorative analysis with Body mass estimates that have no connection to the Torso volume data generated in this study Torso volume in cm3, Body mass in kg #factor coding: Diet (carnivore = 0, herbivore = 1) †models were calculated with interaction term first; if this was not significant, the model was again calculated without the interaction term; estimates for the factor in this table always represent the models where either the interaction was significant or excluded

Table S4. Results of statistical analyses according to Body mass = a (factor) Femur lengthb (and the corresponding factor*Femur length interaction) in Ordinary Least Squares (OLS) and Phylogenetic Generalized Least Squares (PGLS) for extant mammals, birds and reptiles (n=63) Stats λ a b factor# interaction† (95%CI) p (95%CI) p (95%CI) p p Diet OLS (0) 0.004 <0.001 2.98 <0.001 1.75 0.005 n.s. (0.002, 0.007) (2.78, 3.19) (1.20, 2.55) PGLS 0 0.004 <0.001 2.98 <0.001 1.75 0.005 n.s. (0.002, 0.007) (2.78, 3.19) (1.20, 2.55) this is only an explorative analysis with Body mass estimates that have no connection to the Femur length data generated in this study Body mass in kg, Femur length in cm #factor coding: Diet (carnivore = 0, herbivore = 1) †models were calculated with interaction term first; if this was not significant, the model was again calculated without the interaction term; estimates for the factor in this table always represent the models where either the interaction was significant or excluded

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