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15. Neck Posture in Sauropods

Nicole Klein Indiana University Press ePub

ANDREAS CHRISTIAN AND GORDON DZEMSKI

The neck posture in sauropod dinosaurs is a crucial feature that affects their biomechanics, physiology, ecology, and evolution. Yet neck posture and utilization in sauropods are still controversial topics. In this chapter, we use a biomechanical approach to reconstruct the habitual neck posture of sauropods. The analysis is based on a comparison of stresses on the intervertebral cartilage along the vertebral column of the neck. In previous studies on extant animals with long necks, this method has shown to yield reliable results. The habitual neck posture is shown to differ considerably among sauropods. At least in some sauropod species, the long sauropod neck was biomechanically capable of both feeding at great heights and sweeping over a large feeding area without moving much of the body. Differences in neck posture indicate that the feeding strategy varied among sauropods.

A long neck is a characteristic feature of almost all sauropod dinosaurs (McIntosh 1990; but see Rauhut et al. 2005). The necks of some sauropods, such as Brachiosaurus, Barosaurus, Diplodocus, and Mamenchisaurus, reach twice or even more the length of the trunk (e.g., Janensch 1950a, 1950b; Bonaparte 1986; McIntosh 1990). Neck posture is a crucial feature for understanding the ecology, physiology, biomechanics, and evolution of sauropods. Yet the neck posture continues to be a highly controversial subject (Figs. 15.1, 15.2). The long neck has been interpreted as either a means for high vertical browsing (e.g., Bakker 1987; Paul 1987, 1988) or for increasing the horizontal feeding range (e.g., Martin 1987). Taking a single species, Brachiosaurus brancai for example, the range of neck postures suggested extends from horizontal (Frey & Martin 1997; Berman & Rothschild 2005; Stevens & Parrish 2005a, 2005b), to forwardly inclined (Janensch 1950b; Christian & Dzemski 2007), to nearly vertical (Bakker 1987; Paul 1987, 1988; Christian & Heinrich 1998; Christian 2002) (Figs. 15.1, 15.2).

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14. Rearing Giants: Kinetic–Dynamic Modeling of Sauropod Bipedal and Tripodal Poses

Nicole Klein Indiana University Press ePub

HEINRICH MALLISON

Because of their large body masses, sauropod dinosaurs must have required enormous amounts of plant matter to support their metabolism, even if one assumes a much lower metabolic rate in adults than in extant mammals and birds. Therefore, their methods of food acquisition are of interest, specifically how they procured a sufficient volume of food without expending unlikely large amounts of energy during feeding. Some, if not all, sauropods supposedly could rear up onto their hindlimbs to access food at heights beyond the reach of other herbivores, increasing their feeding envelopes without requiring energetically more costly locomotion. Kinetic–dynamic modeling in comparison with elephants indicates that at least diplodocids could rear easily and for prolonged times without significant exertion, while brachiosaurids were probably not capable of extended upright feeding. Modeling results also suggest that optimizing body shape for rearing by a posterior shift of the center of mass may be detrimental to locomotory abilities.

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17. Sauropod Bone Histology and its Implications for Sauropod Biology

Nicole Klein Indiana University Press ePub

P. MARTIN SANDER, NICOLE KLEIN, KOEN STEIN, AND OLIVER WINGS

Bone histology has emerged as the major source of information on life history of dinosaurs, and sauropodomorphs are one of the best-sampled clades. The large long bones (humerus and femur) preserve the most complete growth record, which allows inference on life history, thermometabolism, and other aspects of sauropod biology.

Basal sauropodomorphs have fibrolamellar bone interrupted by regularly spaced growth marks, and termination of growth is recorded in an external fundamental system (EFS). However, in the best-studied basal sauropodomorph, Plateosaurus engelhardti, growth rate deduced from growth mark counts and termination of growth are highly variable (developmental plasticity). Growth series of many taxa of sauropods also show fibrolamellar bone exclusively but differ in that growth marks appear only late in life, or in most taxa only in the EFS. Growth rate and final size are taxon specific, not variable, and genetically predetermined.

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13. Plateosaurus in 3D: How CAD Models and Kinetic–Dynamic Modeling Bring an Extinct Animal to Life

Nicole Klein Indiana University Press ePub

HEINRICH MALLISON

Cad (computer-aided design) software combined with biomechanical considerations can be used to create extremely accurate skeletal reconstructions of dinosaurs and other extinct vertebrates. CAE (computer-aided engineering) methods that are based on such accurate models give insight into the way dinosaurs moved and behaved, and they greatly ease the task of calculating physical properties (such as position of the center of mass) compared to traditional methods. On the basis of a high-resolution 3D model of Plateosaurus, I show that this animal was an agile obligate biped with strong grasping hands. The assessment of possible postures and ranges of motions of the 3D model was done with a CAD program, while the total mass, mass distribution, and the position of the center of mass of the model were assessed with CAE software.

Biomechanics deals with the function and structure of biological systems. This chapter will address certain aspects within this broad field of study, focusing on the mechanics of posture and motion of animals. The prosauropod dinosaur Plateosaurus will be used as a detailed example of how two different modern computer technologies can aid research on extinct animals. CAD (computer-aided design) programs can be applied to the study of large assemblies of objects, for example, bones in a skeletal mount of a dinosaur, without the bother of actually having to lift and support the many, and often heavy, elements. Digital bones, in contrast, have no weight and cannot break, and are easily combined into a virtual skeleton in a CAD program. A virtual skeleton of Plateosaurus is used to assess the posture and range of motion of this animal. Additional information on posture and on locomotion capabilities is derived from CAE (computer-aided engineering) modeling, using a CAD model of the living animal based on the virtual skeleton. The CAE modeling can be used to determine the position of the center of mass (COM) and its shift when the animal moves, as well as joint torques and many other important physical parameters. This approach to biomechanical modeling was termed kinetic–dynamic modeling by Mallison (2007) because it derives information on the kinetics—the movements of the modeled animal—from the dynamics—the forces that cause this movement—and vice versa.

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4. The Diet of Sauropod Dinosaurs: Implications of Carbon Isotope Analysis on Teeth, Bones, and Plants

Nicole Klein Indiana University Press ePub

THOMAS TÜTKEN

Sauropods were megaherbivores that fed predominantly on nonangiosperm vegetation such as gymnosperms, sphenophytes, and pteridophytes. In this chapter, the potential of carbon isotope (δ13C) analysis in skeletal apatite for inferring the diet and niche partitioning of sauropods was tested. The carbon isotope composition of food plants is transferred with a metabolic offset to higher trophic levels along the food chain, which suggests that differences in isotopic composition of sauropod food plants can be used to infer sauropod feeding behavior. For this purpose, the δ13C values of sauropod bones and teeth, primarily from the Late Jurassic Morrison Formation, USA, and the Tendaguru Beds, Tanzania, East Africa, were analyzed, as were the leaves of extant and fossil potential sauropod food plants such as Araucaria, cycads, ferns, horsetails, and ginkgo. The metabolic carbon isotope fractionation between diet and enamel apatite estimated for sauropods is 16‰. By means of this fractionation, a diet based only on terrestria C3 plants can be reconstructed for sauropods. Therefore, sauropods did not ingest significant amounts of plants with high, C4 plant-like δ13C values such as marine algae or C4 plants. However, plants that used crassulacean acid metabolism for biosynthesis and possibly freshwater aquatic plants may have contributed to the diet of sauropods. A more detailed discrimination of exactly which type of food plants was consumed by sauropods based on apatite δ13C values alone is difficult because taxon-specific differences between C3 plants are small and not well constrained. Mean enamel δ13C values of sympatric sauropods differ by approximately 3‰, which may indicate a certain niche partitioning. Differences in mean δ13C values for the living representatives of potential sauropod food plants suggest that a differentiation between low-browsing taxa feeding on ferns or horsetails with lower δ13C values and high-browsing taxa feeding on conifers with higher δ13C values might be possible.

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