Biology of the Sauropod Dinosaurs: Understanding the Life of Giants

By Nicole Klein; Kristian Remes et al. | Go to book overview

15
Neck Posture in Sauropods

ANDREAS CHRISTIAN AND GORDON DZEMSKI

THE NECK POSTURE IN sauropod dinosaurs is a crucial fea-
ture that affects their biomechanics, physiology, ecology,
and evolution. Yet neck posture and utilization in sau-
ropods 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 stud-
ies on extant animals with long necks, this method has
shown to yield reliable results. The habitual neck pos-
ture 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 in-
dicate that the feeding strategy varied among sauropods.


Introduction

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).

Some physiologists doubt that the very long necks of some sauropods, such as Brachiosaurus, could have been held in a more or less vertical position for long periods of time, because if the head was elevated approximately 10 m above the heart, an unlikely high blood pressure would be required to perfuse the brain (Hohnke 1973; Seymour 1976, 2009a; Hargens et al. 1987; Pedley 1987; Dodson 1990; Badeer & Hicks 1996; Seymour & Lillywhite 2000). According to Seymor (2009b), energy expenditures due to higher blood pressure increase greatly with feeding height. To avoid imposing dangerous stresses on the cardiovascular system, sauropods with extreme neck length may have habitually fed at moderate heights, and browsed at relatively greater heights for shorter periods (Dodson 1990). However, the possibility of mechanisms that would have enabled sauropods to cope with the physiological problems associated with a greatly elevated head cannot be excluded. Such mechanisms have been described for giraffes

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