Restoring Maximum Vertical Browsing Reach in Sauropod Dinosaurs

Abstract

The ongoing controversy centered on neck posture and function in sauropod dinosaurs is misplaced for a number of reasons. Because of an absence of pertinent data it is not possible to accurately restore the posture and range of motion in long necked fossil animals, only gross approximations are possible. The existence of a single "neutral posture" in animals with long, slender necks may not exist, and its relationship to feeding habits is weak. Restorations of neutral osteological neck posture based on seemingly detailed diagrams of cervical articulations are not reliable because the pictures are not sufficiently accurate due to a combination of illustration errors, and distortion of the fossil cervicals. This is all the more true because fossil cervical series lack the critical inter-centra cartilage. Maximum vertical reach is more readily restorable and biologically informative for long necked herbivores. Modest extension of 10° between each caudal cervical allowed high shouldered sauropods to raise the cranial portion of their necks to vertical postures that allowed them to reach floral resources far higher than seen in the tallest mammals. This hypothesis is supported by the dorsally extended articulation of the only known co-fused sauropod cervicals. Many sauropods appear to have been well adapted for rearing in order to boost vertical reach, some possessed retroverted pelves that may have allowed them to walk slowly while bipedal. A combination of improved high browsing abilities and sexual selection probably explains the unusually long necks of tall ungulates and super tall sauropods. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:1802-1825, 2017. © 2017 Wiley Periodicals, Inc.

Ontogenetic similarities between giraffe and sauropod neck osteological mobility

“…The same is true for estimating intervertebral space, since differences on the bone texture of the cotyles and condyles of opisthocoelus vertebrae with different amounts of intervertebral space are indistinguishable [12]. Our approach of estimating intervertebral space with the osteologically neutral pose in the newborn giraffe TMM M-16050 showed two things: (i) that in the newborn specimen, only the ONP rendered an intervertebral space which came close to the intervertebral space observed in the articulated CT-Scan of the specimen and, (ii) neutral bone only posture (NBOP), in which the rims of the vertebral centra are situated parallel [21], greatly underestimates the amount of intervertebral space as observed in the articulated CT-Scan of the specimen (Fig 2C vs. Fig 3C).…”

“…In this work, ONP is the full articulation of the zygapophyseal facets, with complete overlap of the facet outlines in all three anatomical planes (antero-posterior, lateral-medial, dorso-ventral). Neutral Bone Only Posture (NBOP sensu Paul [21]) was coined for accounting not only for the best possible articulation of pre-and postzygapophyseal facets, but also to have the rims of the vertebral centra parallel (Fig 3; see discussion).…”

“…The following hypotheses have been evaluated: (i) osteology alone does not allow to estimate the amount of intervertebral space [20,21], (ii) some neck postures attained in life require disarticulating vertebrae [10,12], (iii) the amount of intervertebral space diminishes with ontogenetic development [12], and (iv) the range of motion of the neck increases with ontogenetic National Boubou Hama (MNN, Niamey, Niger). The digital fossils used to build the virtual skeleton are deposited at the Museo Paleontológico de Elche.…”

High browsing skeletal adaptations in Spinophorosaurus reveal an evolutionary innovation in sauropod dinosaurs

“…Those with longer forelimbs relative to their hindlimbs are interpreted as having high browsing capabilities 14,15 . Camarasaurus is a genus typically interpreted as a capable medium to high browser based on its shoulder height 14,33 , with a humerus to scapula ratio around 0.74 and a femur to humerus ratio around 1.37. Both the humerus to scapula ratio (0.816) and the estimated femur to humerus ratio (1.21) of Spinophorosaurus indicate a relatively larger humerus than that of Camarasaurus.…”

“…Therefore the preserved forelimb and pectoral girdle elements of Spinophorosaurus are relatively longer than those of Camarasaurus. All in all, Spinophorosaurus had a humerus and scapula relatively longer, making its shoulders relatively taller than those of most known sauropods, with the exception of at least Atlasaurus 34 brachiosaurids 10,33,35 and some titanosaurs ( Table 1, Fig. 2B).…”