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auropod hatchlings may have been only a meter long from head to tail (Chiappe et al. 1998, 2001) and weighed in at less than 10 kg (Breton et al. 1985; Weishampel and Horner 1994), while many adult sauropods attained sizes rivaling those of extant whales (Appenzeller 1994; Seebacher 2001; Erickson et al. 2001). This range of sizes is greater than for any other dinosaurian lineage , and includes the largest terrestrial vertebrates ever to inhabit the planet. In addition to this dramatic range of ontogenetic size variability , sauropod sizes vary interspecifically (fig. 11.1). The Romanian titanosaur Magyarosaurus has been dubbed the “smallest of the largest” because of its minute adult stature (5 m [Jianu and Weishampel 1999]). Similarly , the saltasaurids Saltasaurus and Neuquensaurus are on the “small” end of sauropod size, reaching adult lengths of only 7 m and weights of 10,000 kg (Powell 1986, 1990, 2003). Conversely, Argentinosaurus, Paralititan, and Seismosaurus push the envelope of size for land-dwelling vertebrates (Anderson et al. 1985; Coe et al. 1987; Gillette 1991; Appenzeller 1994; Seebacher 2001; Smith et al. 2001). As adults, these giants are estimated to have reached lengths of more than 30 m and weighed between 30 and 100 tons. The growth strategies that permitted sauropods to attain such massive proportions have historically been a topic of great interest, but until recently they remained among the greatest of biological mysteries. In early investigations , workers extrapolated from reptilian growth rates and hypothesized that giant sauropods would have taken decades to reach sexual maturity and well over a century to attain their enormous adult sizes (e.g., Case 1978b; Calder 1984). More recent workers have focused specifically on evidence gleaned from bones and have revealed astounding new data that indicate that sauropod growth rates soared through most of ontogeny (e.g., Ricqlès 1968a,b; Reid 1981, 1990, 1997; Rimblot-Baly et al. 1995; Curry 1998; Sander 2000, 2003; Erickson et al. 2001; Curry Rogers et al. 2003; Sander and Tückmantel 2003). On the outside, fossilized bones provide the raw data on which we base our interpretation of sauropod anatomy, relationships, function, and biomechanics, and our confidence in the 303 ELEVEN Sauropod Histology MICROSCOPIC VIEWS ON THE LIVES OF GIANTS Kristina Curry Rogers and Gregory M. Erickson S restored version of long-extinct sauropods rests almost exclusively on evidence obtained from fossil bones. The sizes and body proportions outlined above are readily reconstructed from the skeleton, even when remains are relatively fragmentary. Muscle scars on bones help determine where muscles originate and insert, and the resultant pattern of musculature dictates reconstructed body shape, as well as our interpretations of bone and muscle synergy and biomechanical function (chapters 6 and 8). Similarly, osteological correlates of soft tissues preserved in fossil bones (e.g., pneumatic fossae ; chapter 7) make it possible to reconstruct unpreserved soft parts that may never be found in the fossil record. For example, Witmer (2001) reconstructed Diplodocus with terminally positioned external nares on the basis of soft tissue correlates in the skull. The gross morphology of bones thus enriches the story of sauropod evolution. Through osteology we document the debut and demise of major lineages and the evolutionary tale told by the trail of characters observed in fossil skeletons. The internal architecture of fossil bones documents patterns of bone deposition and remodeling and can sometimes allow access to the portions of the bone growth record throughout ontogeny. The clues preserved in fossil bone tissue thus provide the necessary comparative data for choosing among extant analogues, and allow for sauropod growth rate quantification on microstructural and organismal levels. Bone histology breathes new life into fossil bones and offers a rigorous, testable means of addressing hypotheses of sauropod growth rates and life history. Did sauropods grow indeterminately? Did sauropods grow at constant rates throughout ontogeny, or did they experience regular cycles of relative growth rate variation? When did sauropods attain maturity? How long did it take sauropods to reach their massive adult sizes? Did all sauropods exhibit the same basic growth strategy? Along the same lines, is sauropod histology relevant to sauropod phylogeny? The answers to these questions lie under microscopes and deep within sauropod bone tissue. In this chapter we consider sauropod growth throughout ontogeny from both histological and whole-body perspectives. We first provide a primer on relevant bone histological patterns, followed by a brief overview of the evidence from living and fossil vertebrate taxa relevant to qualitative interpretations of sauropod bone tissue. We outline a method...

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