The Articulation of Sauropod Necks: Methodology and Mythology

Abstract

Sauropods are often imagined to have held their heads high atop necks that ascended in a sweeping curve that was formed either intrinsically because of the shape of their vertebrae, or behaviorally by lifting the head, or both. Their necks are also popularly depicted in life with poses suggesting avian flexibility. The grounds for such interpretations are examined in terms of vertebral osteology, inferences about missing soft tissues, intervertebral flexibility, and behavior. Osteologically, the pronounced opisthocoely and conformal central and zygapophyseal articular surfaces strongly constrain the reconstruction of the cervical vertebral column. The sauropod cervico-dorsal vertebral column is essentially straight, in contrast to the curvature exhibited in those extant vertebrates that naturally hold their heads above rising necks. Regarding flexibility, extant vertebrates with homologous articular geometries preserve a degree of zygapophyseal overlap at the limits of deflection, a constraint that is further restricted by soft tissues. Sauropod necks, if similarly constrained, were capable of sweeping out large feeding surfaces, yet much less capable of retracting the head to explore the enclosed volume in an avian manner. Behaviorally, modern vertebrates generally assume characteristic neck postures which are close to the intrinsic curvature of the undeflected neck. With the exception of some vertebrates that can retract their heads to balance above their shoulders at rest (e.g., felids, lagomorphs, and some ratites), the undeflected neck generally predicts the default head height at rest and during locomotion.

A validated method for modeling anthropoid hip abduction in silico

“…The increased angle of abduction in the gibbon increases the spatial envelope of the hindlimb, positioning more supports within immediate reach compared with the macaque. Similar spatial concepts related to locomotor ability (Kapandji, ; Grand, ; Prost, ) and also feeding performance (Stevens and Parrish, ; Stevens, ) have been presented by other workers. In vivo hip joint ranges of motion from Hammond () guided the ranges of motion illustrated here.…”

“…Assessing joint mobility in fossil animals is critical for reconstructing their functional morphology and locomotor adaptation (Jenkins, ; Jenkins and Camazine, ; Ruff, ; Swartz, ; Ward, ; Ward et al, ; MacLatchy, ; Hamrick, ; MacLatchy and Bossert, ; Gatesy et al, ; Hutson and Hutson, ; Pierce et al, ; Stevens, ; Gatesy and Baier, ). To do this requires estimating ranges of motion from bony anatomy.…”

Functional morphology of the primate head and neck

“…Many early descriptions of primate cervical morphology as a whole concluded that skeletal variation was limited and that the region was thus relatively uninformative regarding functional or phylogenetic questions (e.g., Toerien, 1961; Ankel 1967 Ankel , 1970 Ankel , 1972. Notable exceptions include Slijper (1946) and Schultz (1961). Slijper's 1946 work investigated the presacral vertebral column across animals and developed several body-axis models stilled used today (e.g., Clauser, 1980;Shapiro, 1991;Dunbar et al, 2008;Stevens, 2013). Furthermore, the author recognized the positive relationship between body size and spinous process size and argued that the differences in cervical spinous process length between humans, great apes, and monkeys was related to head posture and position maintenance (see Toerien (1961) as well).…”

“…Notable exceptions include Slijper (1946) and Schultz (1961). Slijper's 1946 work investigated the presacral vertebral column across animals and developed several body-axis models still used today (e.g., Clauser, 1980;Shapiro, 1991;Dunbar et al, 2008;Stevens, 2013). Furthermore, the author recognized the positive relationship between body size and spinous process size and argued that the differences in cervical spinous process length between humans, great apes, and monkeys was related to head posture and position maintenance (see also Toerien, 1961).…”

Neck length and mean arterial pressure in the sauropod dinosaurs

“…The work of Christian (2010), Christian et al (2013) and Stevens (2013) suggests that the natural neck pose of the sauropods was horizontal. Taylor and colleagues (Taylor et al, 2009;Taylor and Wedel, 2013) have proposed sauropods held their neck in an erect 'S' shape -like a swan, for example.…”