Evolutionary Morphology of the Neck System in Ratites, Fowl and Waterfowl

Abstract

The avian neck is a complex, kinematically redundant system that controls the position and orientation of the head. The kinematic redundancy is resolved by movement principles, which result in characteristic movement patterns. General neck movement patterns are compared between Ratites, Fowl and Waterfowl in order to nd a relationship with anatomical differences and to identify the biological role(s) to which neck movement is adapted. Kinematic analyses show that Fowl move their vertebrae according to a minimal rotation principle that maximizes rotation ef ciency. The resulting movement pattern shows rotations in some joints, while keeping the other vertebrae as straight bars. Waterfowl show a pattern of successive, rather than simultaneous rotations of vertebrae, limited to the rostral part of the neck. A third movement pattern is found in Ratites, which show successive rotations of the vertebrae in the middle region of the neck. The ratite-pattern is related to large vertical head trajectories, and is occasionaly also found in the Chicken. However, due to large body movements in the Chicken, head trajectories are relatively much shorter than in the Rhea. A kinematic neck model based on the minimal rotation principle only produces the Waterfowl pattern if a constraint on the movement of the caudal vertebrae is introduced. We conclude that a fundamental change occurred in the movement pattern of the Waterfowl neck, which is energetically advantageous and an adaptation to aquatic feeding.

Inter-Vertebral Flexibility of the Ostrich Neck: Implications for Estimating Sauropod Neck Flexibility

“…The general pattern of a division of the neck into three sections with varying flexibility concurs with previous research into the flexibility of avian necks ([43]: pg. 248, fig.…”

“…However, it should be noted that there are some differences in inter-vertebral articulations between these taxa (heterocoelous in ostriches, opisthocoelous in sauropods) that would affect direct comparisons of their flexibility. It is thought that ratites evolved elongate necks independently on several occasions [43]. Three female ostrich necks were used in this study, donated by MNS Ostriches Ltd, U.K. All three were humanely destroyed at around the same age (∼ 6 months).…”

The Articulation of Sauropod Necks: Methodology and Mythology

“…The osteologically neutral pose or ONP [30]–[32] (Figure 1) defines the state of an deflected vertebral column, relative to which extremes of joint dorsiflexion, ventriflexion, and mediolateral flexion are subsequently measured [15], [63]–[65], [48]. Additional refinement to the operational definition of ONP is warranted, especially when the joint geometry suggests differing degrees of dorsal versus ventral flexibility, but a satisfactory convention is to define ONP as when the pre- and post- zygapophyses are centered and maximally overlapping, which often coincides at the centrum to parallel margins of synovial capsule surrounding the condyle-cotyle.…”

The rhea, a ratite native to South America

“…The myology of the neck in the rhea is different from that in chickens and waterfowl. The Muscularis biventer cervicus does not have the characteristic two muscle bellies connected by a tendon, but several series of up to three parallel tendons are connected by muscle fibers (Van der Leeuw, 2001). Furthermore, the ligamentum nuchae in the neck of the Greater rhea splits ventrally into two halves as the neural spines become bifurcated in the posterior cervical region (Tsuihiji, 2004).…”

“…The quadrate and palatepterygoid complex in the rhea move forward pushing the upper bill upward (Gussekloo et al, 2000). Rheas keep their bodies more or less stationary during feeding (Van der Leeuw et al, 2001).…”