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Home , Barosaurus, Cetiosaurus, Mamenchisauridae, Neosauropoda, Puertasaurus, Supersaurus

PNEUMATICITY, NECK LENGTH, AND BODY SIZE IN SAUROPODS Mathew Wedel, UCMP, Berkeley, CA 94720-4780 · [email protected] · http://www.sauroposeidon.net/

ABSTRACT UPDATED! 4. HOW ARE THE VARIABLES RELATED? Long necks are synapomorphic for sauropods, and additional neck elongation occurred independently Organisms and their traits are not statistically independent because they are united by in different sauropod . Increases to 15 or more occurred at least four times, in common descent. Phylogenetically independent contrasts must be used to remove the effect of mamenchisaurs, diplodocids, , and . Necks longer than 10 meters also evolved at phylogeny from studies of character correlation (Felsenstein 1985). I used the PDAP module in least four times, in mamenchisaurs, diplodocids, brachiosaurids, and giant titanosaurs like . The Mesquite v1.12 (Milford et al. 2005, Maddison & Maddison 2006) to test correlations among the longest-necked sauropod for which a rigorous estimate is possible is , which had a neck at least following: absolute neck length (ANL), trunk length (TL), femur length (FL), cervical count (CC), 13.7 meters long. The sauropods with the longest necks, such as Supersaurus, , and maximum elongation index (MEI), proportional neck length (PNL; ANL/TL), air space proportion Puertasaurus, are also among the largest known terrestrial vertebrates. (ASP). Pneumatic vertebrae facilitated neck elongation in sauropods. The lightest sauropod vertebrae were I ran two sets of tests. The first set included only the 15 taxa for which ASP values are known 89% air by volume and had a specific gravity (SG) of 0.22. By comparison, cervical vertebrae of the or could be reasonably estimated (see Table 1). The second set of tests included all 19 taxa in Table giraffe have an SG of 1.3, and are scarcely lighter than other postcranial elements (SGs up to 1.7). The 1, but did not include the ASP variable. Both sets of tests were run using four different tree cervical column of is 8.5 meters long but the vertebrae would have totaled less than 600 topologies: (1) the topology of Wilson (2002), with , , and kilograms—about the same mass as the ’s paired humeri, which are each only two meters long. C added, and prosauropods monophyletic; (2) the same topology but with prosauropods paraphyletic; The relationships between body size, neck length, and pneumaticity can be evaluated statistically using (3) the topology of Upchurch et al. (2004), with Massospondylus and Plateosaurus added, and EI phylogenetically independent contrasts. I used the PDAP module in Mesquite v1.06 to test the correlations prosauropods monophyletic; and (4) the topology of Rauhut et al. (2005), with Massospondylus, among femur length (FL), trunk length (TL), absolute neck length (ANL), proportional neck length (PNL; 16 Plateosaurus, and Cetiosaurus added, and prosauropods monophyletic. These phylogenetic neck length/dorsal length), cervical count (CC), maximum elongation index (MEI), and air space proportion rearrangements had very little effect on character correlation. ANL and FL are only correlated when (ASP) in 14 sauropodomorphs. ASP and the size-independent measures of neck length (PNL, CC, and MEI) the topology of Upchurch (2004) is used; otherwise the same statistically significant correlations form a pool of mutually-correlated variables (at p<0.05), as do the variables related to absolute size (FL, TL, were detected under all topologies. In addition, the same relationships are found among the and ANL). However, few significant correlations link the two pools. Neck elongation in sauropods is tied to variables other than ASP in the tests with 15 and 19 taxa. Statistical relationships among the pneumaticity but largely independent from size-related variables. variables are shown below; black lines indicate significant correlations (r2 > 0.65, p < 0.05).

INTRODUCTION MEI NECK PROPORTIONS Sauropods were the largest and longest-necked terrestrial of all time. The presacral vertebrae of most sauropods were filled with pneumatic spaces that would have greatly reduced the mass of the Figure 3. At roughly 600 kg, the 8.5-meter cervical series of Brachiosaurus had about 12 FL PNL vertebral column. The goal of this project is to answer the following questions: 15 the same mass as the animal’s paired 2-meter humeri.

C 1. How many times did characters related to neck length and pneumaticity evolve ANL independently in sauropods? EI CC 3. HOW MUCH DOES PNEUMATICITY MATTER? 2. How long was the longest neck of any sauropod? TL In contrast to prosauropods and sauropods, mamenchisaurids and neosauropods had extensive 2. Was pneumaticity important in reducing the mass of sauropod vertebrae? vertebral pneumaticity. Percent pneumatization of the presacral vertebrae—the number of pneumatic elements ASP divided by the total presacral count—rose to a maximum early in sauropod and was subject to only 3. Are variables related to pneumaticity, neck length, and body size statistically correlated? ABSOLUTE SIZE PNEUMATICITY one notable reversal, in dicraeosaurids (Table 1). The idea that pneumatic bones are lighter than marrow bones is intuitively appealing, but it needs to be tested. In particular, we need to know how much lighter pneumatic The variables related to absolute size (ANL, FL, and TL) and neck proportions (CC, MEI, 1. HOW MUCH HOMOPLASY? vertebrae are compared to apneumatic vertebrae if we want to understand any functional advantage. and PNL) share many correlations within pools but few correlations between pools: absolute neck Resolving characters on a phylogeny is a powerful tool for exploring evolutionary patterns. In The presacral vertebrae of most neosauropods were on average 60% air by volume (Wedel 2005, length is correlated with maximum elongation index and proportional neck length (and the latter particular, repeated evolution of characters in closely related lineages can elucidate shared developmental Woodward 2005, Schwarz & Fritsch 2006). The centrum walls, laminae, septa, and struts that composed the may be the result of autocorrelation, because PNL is based in part on ANL). Pneumaticity is processes and evolutionary trends. I collected character data by CT scanning and personal observation when Missing elements vertebrae are primarily made up of compact bone (Reid 1996). The specific gravity (SG) of compact bone is correlated with absolute and proportional neck length and cervical count. Importantly, in all possible, and from the literature when necessary (Table 1). The phylogeny shown here (Fig. 1) is broadly EI 2.0 in most tetrapods, so an element with an ASP of 0.60 would have an in vivo SG of 0.8. Some sauropod permutations none of the pneumaticity or neck proportion variables are correlated with femur length C vertebrae were much lighter. For example, Sauroposeidon had ASP values up to 0.89 and thus SG as low as or trunk length. congruent with several recent cladistic analyses (Wilson 2002, Upchurch et al. 2004, Rauhut et al. 2005, Increases in cervical count 17 Harris 2006), but agnostic about the relationships of several taxa that have proven to be unstable in those 15 0.22. On the other hand, many basal sauropods had ASPs of 0.30-0.40 and SG of 1.2-1.4. analyses (e.g., Cetiosaurus, , and ). To explore the impact of pneumaticity on skeletal construction, I estimated the in vivo mass of the CONCLUSIONS cervical skeleton of Brachiosaurus. From CT scans it is possible to calculate the volume of bone tissue in a The evolution of long necks in sauropods is marked by the repeated evolution of several important EI Elongation index > 4.0 1. Many characters related to neck length and pneumaticity evolved in parallel in different single and thus determine the mass of the element. I multiplied the mass of a single vertebra by scale characters, including the number of cervical vertebrae, the length of the individual vertebrae, the complexity 15 sauropod lineages. factors to determine the masses of the other vertebrae in the neck, and added the resulting values to estimate of vertebral internal structure, and the ratio of bone to air space. 2. Necks longer than 10 meters evolved independently in four sauropod clades. Supersaurus C Complex internal structure the mass of the whole cervical series. The mass of the cervical column of Brachiosaurus is 590 kilograms. For Cervical Count—If the primitive number of cervical vertebrae in is 13 (Gomani 2005), had the longest neck of any known animal: at least 13.7 meters, and possibly more than 16 the sake of comparison, I used graphic double integration (Hurlburt 1999) to estimate the mass of a then increases to 15 or more cervicals occurred at least four times: in the , , meters. Brachiosaurus humerus at 290 kg. The animal’s humeri are each 2 meters long but together they weighed as Euhelopus, and Rapetosaurus. Alternatively, 15 or more cervicals may be primitive for , the 3. Pneumatic presacral vertebrae of neosauropods were, on average, 60% air by volume, and much as the 8.5-meter cervical series. The presacral vertebrae of Brachiosaurus have an average ASP of 0.67 lower counts in and may be reversals, and increases to 15 or more cervicals may therefore half as dense as the marrow bones of mammals. Figure 1. The evolution of long necks in sauropods. and a mean SG of 0.66. The cervical vertebrae of the giraffe are almost exactly twice as dense, with SG of 1.3 have only happened three times. The relatively primitive count of 13 cervicals in Brachiosaurus is 4. When the effects of phylogeny are removed by the use of independent contrasts, neck (Van Schalkwyk et al. 2004). If the cervical vertebrae of Brachiosaurus were built like those of a giraffe, they noteworthy; no other known sauropod had such a long neck with so few vertebrae. See text and Table 1 for details and data. elongation is related to pneumaticity but not to absolute size. would weigh twice as much. Elongation Index—The elongation index (EI) is the length of a vertebra divided by its diameter. The cervical vertebrae of basal sauropodomorphs did not exceed an EI of 3.2. Elongate vertebrae with EIs greater 2. HOW LONG WAS THE LONGEST NECK? than 4.0 evolved independently at least three times, in Mamenchisauridae, Diplodocidae, and LITERATURE CITED Titanosauriformes. The sauropods with the most elongate vertebrae are the brachiosaurid Sauroposeidon and Supersaurus is without question the longest-necked animal Many authors have speculated about the hemodynamic Table 1. Neck length, body size, and pneumaticity variables for taxa included in this study. with preserved cervical material. Jim Jensen recovered a single and respiratory debits imposed by the long necks of sauropods Britt. 1993. Pneumatic postcranial bones in and Sauropodomorph Dinosaurs. Indiana Univ. Press. the basal somphospondylan ; in both taxa the maximum EI is greater than 6.0. Cervical Neck Trunk Femur Proportional Max. Elongation % Presacral Air Space other archosaurs. Ph.D. thesis, Univ. of Calgary. Midford et al. 2005. PDAP Package of Mesquite. Version cervical vertebra of Supersaurus from in (Hohnke 1973; Seymour 1976; Choy & Altman 1992; Daniels & Choy & Altman. 1992. Lancet 340:534-536. 1.07. Count Length (m) Length (m) Length (cm) Neck Length Index Pneumaticity Proportion Source Vertebral Internal Structure—In most basal sauropods, the centrum of each vertebra contains a pair western . The vertebra, BYU 9024, has a total length of Pratt 1992; Gunga et al. 1995; Badeer & Hicks 1996; Seymour Cooper. 1981. Occasional Papers of the National Museum Novas et al. 2005. Revista del Museo Argentino de CC ANL TL FL PNL = ANL/DL MEI (- atlas) ASP of large chambers and has a cross-section similar to an I-beam. In more derived sauropods the number of 1378 mm. Neck length estimates for Supersaurus vary depending & Lillywhite 2000). Whatever problems came along with a 9-m and Monuments of Rhodesia, Series B 6:689-840. Ciencias Naturales 7:37-41. Massospondylus 10 0.8 0.8 60 1.02 3.0 0 0.00 Cooper 1981 Curry-Rogers & Forster. 2001. Nature 412:530-534. Osborn & Mook. 1921. Memoirs of the AMNH 3:247–287. pneumatic cavities increases and the vertebrae become honeycombed with small cavities. Complex, many- on the taxon chosen for comparison and the serial position neck, sauropods were certainly adept at achieving and exceeding Daniels & Pratt. 1992. Comparative Biochemistry and Powell. 1992. pp. 165-230 in Los Dinosaurios y Su chambered vertebrae evolved independently at least three times, in Mamenchisauridae, Diplodocidae, and assumed for BYU 9024. The vertebra shares many similarities that mark, as evidenced by , Supersaurus, Plateosaurus 10 1.0 1.4 80 0.74 2.8 0 0.00 Huene 1926, pers. obs. Physiology 101A:43-46. Entorno Biotico. Instituto Juan de Valdes, . Felsenstein. 1985. American Naturalist 125:1-15. Rauhut et al. 2005. Nature 435:670-672. 13 1.3 1.5 87 0.87 3.2 28 0.10† Zhang 1988 Titanosauriformes. with that are not found in other diplodocines, Sauroposeidon, and Puertasaurus. It is of particular interest that Gilmore. 1936. Memoirs of the Carnegie Museum 11:175- Reid. 1996. BYU Geology Studies 41:25-72. Air Space Proportion—The air space proportion (ASP) of a bone is the proportion of its volume taken including a proportionally long centrum, dual posterior all of the studies just mentioned used , Barosaurus, 16 8.5 2.2 134 3.79 4.9 100 -- He et al. 1988 300. Russell & Zheng. 1993. Canadian Journal of Earth Science centrodiapophyseal laminae, a low neural spine, and ventrolateral Brachiosaurus, or Mamenchisaurus as models. At a probable Gomani. 2005. Palaeontologica Electronica 8(1) 27A:1-37. 30:2082-2095. up by pneumatic cavities. The presacral vertebrae of most neosauropods had ASPs between 0.60 and 0.70— Mamenchisaurus 19 9.5 2.7 128 3.52 4.2 100 -- Young & Zhao 1972, pers. obs. Gunga et al. 1995. Naturwissenschaften 82:190-192. Salgado & Bonaparte. 1991. Ameghiniana 28:333-346. flanges that connect to the parapophyses. The neural spine of BYU 16.2 m, the neck of Supersaurus was 70% longer than that of Cetiosaurus 13 2.9 1.8 166 1.61 3.2 100 0.30† Upchurch & Martin 2002, pers. obs. Harris. 2006. Journal of Systematic Palaeontology 4:185- Schwarz & Fritsch. 2006. Eclogae Geologicae Helvetiae as lightly built as the bones of most birds (Wedel 2005). The only exceptions among neosauropods are the 9024 is very low and only very slightly bifurcated at its apex. In any sauropod whose blood pressure or respiratory dead space 198. 99:65–78. dicraeosaurids, which have fewer pneumatic vertebrae and much lower ASPs (< 0.20). In contrast to the Jobaria 12 4.0 3.2 180 1.25 2.1 58 0.40† Sereno et al. 1999, pers. obs. Hatcher. 1901. Memoirs of the Carnegie Museum 1:1-63. Sereno et al. 1999. Science 286:1342-1347. these characters, it is most similar to C9 of Barosaurus. However, has been calculated. In other words, no previous investigation Hatcher. 1903. Memoirs of the Carnegie Museum 2:1-72. Seymour. 1976. Nature 262:207-208. Haplocanthosaurus 13 2.3 1.9 128 1.21 3.0 100 0.40 Hatcher 1903, pers. obs. majority of neosauropods, Cetiosaurus, Jobaria, and Haplocanthosaurus had much lower ASPs, around 0.40. the proportions of the centrum of BYU 9024 are more similar to of the physiological limits of sauropod necks has come within He et al. 1988. The Middle fauna from Seymour & Lillywhite. 2000. Proceedings of the Royal those of C14 of Barosaurus, which is the longest vertebra in the a literal stone’s throw of what we now know to be possible. 13 1.5 1.3 105 1.15 2.1 67 -- Salgado & Bonaparte 1991 Dashanpu, Zigong, Sichuan, Vol. IV, The Sauropod Society of London B 267:1883-1887. Unfortunately, these three taxa have proven unstable in recent phylogenetic analyses, especially with respect Dinosaurs (2). Sichuan Scientific and Technological Upchurch & Martin. 2002. Palaeontology 45:1049-1074. to the fundamental neosauropod divergence. It is therefore unclear whether high ASPs evolved independently neck. BYU 9024 is 1.6 times as long as C14 and 1.9 times as long 11 2.2 1.8 128 1.22 2.2 61 0.20 Janensch 1929, Schwarz & Fritsch 2006 Publishing House. Upchurch et al. 2004. pp. 259–324 in The Dinosauria, 2nd Hohnke. 1973. Nature 244:309-310. ed . Univ. of California Press. in Diplodocidae and , or if a high ASP is synapomorphic for . To further complicate as C9. If it was built like that of Barosaurus, the neck of 15 4.9 2.2 179 2.23 3.3 100 0.58 Glimore 1936, pers. obs. Supersaurus was at least 13.7 m (44.8 ft) long, and may have been Huene. 1926. Geologische und Palaontologische Van Schalkwyk et al. 2004. Journal of Zoology 264:307- matters, no relevant data have been published for any mamenchisaurid. In published descriptions, the internal Diplodocus 15 6.1 2.8 154 2.18 4.9 100 0.53 Hatcher 1901, pers. obs. Abhandlungen 15:129-179. 315. Hurlburt. 1999. Journal of Vertebrate Wedel. 2005. pp. 201–228 in The Sauropods: Evolution as long as 16.2 m (53.2 ft). Barosaurus 16 8.5 2.4 144 3.54 5.3 100 0.70 McIntosh 2005, pers. obs. structure of mamenchisaurid vertebrae is described as a honeycomb of small cavities (Young and Zhao 1972, Based on new material from Wyoming, Lovelace et al. Figure 2. The three longest vertebrae ever 19:338–350. and Paleobiology. Univ. of California Press. Russell and Zheng 1993). It therefore seems likely that mamenchisaurids had ASPs similar to those of most 12 4.0 2.5 180 1.60 3.5 100 0.57 Osborn & Mook 1921, pers. obs. Janensch. 1929. Palaeontographica, Supplement 7, 2(1):37- Wedel et al. 2000. Acta Palaeontologica Polonica 45:343- (2005) proposed that Barosaurus was the most basal diplodocid described. All are midcervical vertebrae 133. 388. neosauropods. If that is the case, then high ASPs (> 0.50) evolved at least twice, in Mamenchisauridae and and that Supersaurus was most closely related to Apatosaurus (the Brachiosaurus 13 8.5 3.8 200 2.24 5.4 100 0.67 Janensch 1950, 1961, pers. obs. Janensch. 1950. Palaeontographica, Supplement 7, 3(2):27- Wilson. 2002. Zoological Journal of the Linnean Society and substantially longer than one meter. Euhelopus 17 4.0 1.6 89 2.50 4.0 100 0.65† Wiman 1929, Britt 1993 93. 136:217–276. Neosauropoda. similarities between Barosaurus and Supersaurus would then be Janensch. 1961. Palaeontographica, Supplement 7, Wiman. 1929. Palaeontologia Sinica 6:1-67. Summary—Many characters related to neck length and pneumaticity evolved independently in symplesiomorphies). BYU 9024 does not closely resemble any of Puertasaurus from Novas et al. 2005; Malawisaurus 13 3.4 1.7 95 2.00 4.7 100 0.65 Gomani 2005, pers. obs. 3(4):177-235. Woodward. 2005. Journal of Vertebrate Paleontology Lovelace et al. 2005. Journal of Vertebrate Paleontology 25:132A. the cervical vertebrae of Apatosaurus. If we conservatively Rapetosaurus 16 1.9* 0.8* 100 2.38 5.1 100 -- Curry-Rogers & Forster 2001 Mamenchisauridae, Diplodocidae, and Titanosauriformes. Within Titanosauriformes, brachiosaurids are 25:84A-85A. Young & Zhao. 1972. Institute of Vertebrate Paleontology estimate that it was the longest vertebra in the neck, the total neck Sauroposeidon and Supersaurus characterized by a relatively small number of very elongate cervical vertebrae. The vertebrae of most Saltasaurus 13 1.8 1.5 150 1.20 2.7 100 0.69 Powell 1992 Maddison & Maddison. 2006. Mesquite Version 1.12. and Paleoanthropology Monographs, A, 8:1-30. length would still be 13.7 meters, substantially longer than the photographed by the author. http://mesquiteproject.org. Zhang. 1988. Journal of the Chengdu College of Geology somphospondylans are proportionally shorter, but the number of cervicals is increased in some taxa. * Estimated from press photos of assembled skeleton. McIntosh. 2005. pp. 38-77 in Thunder-: the 3:1-87. neck of any other known sauropod. † Estimated from photos or personal examination (as opposed to cross-sections).