6. Digital Reconstructions of Sauropod Dinosaurs and Implications for Feeding

Abstract

n recent years, sauropods HAVE been interpreted primarily as quadrupedal herbivores, with sympatric taxa differentiated in their feeding behavior presumably according to their dentition and feeding height in a quadrupedal stance (e.g., Fiorillo 1998; Upchurch and Barrett 2000). In order to generate detailed hypotheses concerning sauropod paleoecology, it is essential to start with as accurate a reconstruction of their body plans as can be afforded from their fossils. An accurate rendering of the life posture of a sauropod is necessary in order to determine the feeding envelope for each taxon in its conventional quadrupedal stance. We review here the body plan of several major sauropod groups, emphasizing the use of whole-body reconstructions to determine the approximate head height when the animal was standing quadrupedally, supporting its weight symmetrically from left to right, and holding the axial skeleton in an undeflected state. The undeflected state is termed the “neutral pose,” defined geometrically, and analyzed on the basis of osteological determinants in extant vertebrates as a guide to their reconstruction for sauropods. Neutral position head height is one key point for analyzing variation in feeding behaviors across sauropods, another being variation in dentition; both are set against the backdrop of available fodder. What was the relationship between a sauropod’s preferred feeding height and the height at which its head was held when the neck was undeflected? A bridging assumption is necessary to relate these two parameters for an extinct species. The habitual feeding posture of a terrestrial herbivore can relate to the neutral position of its neck in three ways: (1) the herbivore can deflect its neck ventrally relative to the neutral position for browsing, or “browse by ventriflexion” (BV); it can raise its neck relative to the neutral position, or “browse by dorsiflexion” (BD); or it can feed at or near the neutral position of the neck, or “browse neutrally”(BN). As browsing behavior is not directly preserved in the fossil record, it is necessary to consider the phylogenetic and functional distribution of these three feeding models among extant tetrapods. The form of browsing (BV, BD, or BN) is, in principle, independent of the neutral pose head height (relative to shoulder height) of a given SIX