Flexibility Along the Neck of the Ostrich (Struthio camelus) and Consequences for the Reconstruction of Dinosaurs With Extreme Neck Length Gordon Dzemski and Andreas Christian* Institut fu ¨r Biologie, Department IV, Universita ¨ t Flensburg, 24943 Flensburg, Germany ABSTRACT The gross morphology and the flexibility along the neck of the ostrich (Struthio camelus) were examined using fresh tissue as well as neck skeletons. The results of the morphologic studies were compared with results from observations of living ostriches. The investigation was focused on differences in the morphol- ogy and the function between different sections of the neck. Additionally, the function of major dorsal neck liga- ments was examined, including measurements of force- strain-relations. Comparative studies of giraffes (Giraffa camelopardalis) and camels (Camelus bactrianus) were conducted to find relations between the flexibility along the neck and the general feeding strategy. The examina- tions revealed that the neck of the ostrich can be divided into four sections with different functions. The first is the atlas-axis-complex which is responsible for torsion. The adjacent cranial section of the neck is flexible in dorso- ventral and lateral directions but this part of the neck is usually kept straight at rest and during feeding. Dorso- ventral flexibility is highest in the middle section of the neck, whereas the base of the neck is primarily used for lateral excursions of the neck. For giraffes and camels, the posture and utilization of the neck are also reflected in the flexibility of the neck. For all three species, it is possible to reconstruct the pattern of flexibility of the neck by using the neck skeletons alone. Therefore, it appears reasonable to reconstruct the neck utilization and the feeding strategies of dinosaurs with long necks by deriving the flexibility of the neck from preserved ver- tebrae. For Diplodocus carnegii the neck posture and the feeding strategy were reconstructed. Two neck regions, one around the 9th neck vertebra and the second at the base of the neck, indicate that Diplodocus, like the os- trich, adopted different neck postures. The neck was probably kept very low during feeding. During interrup- tions of the feeding, e.g., in an alert, the head could have been lifted in an economic way by raising the cranial sec- tion of the neck. During standing and locomotion the head was probably located well above the shoulders. J. Morphol. 268:701–714, 2007. Ó 2007 Wiley-Liss, Inc. KEY WORDS: neck; ostrich; flexibility; morphology; biomechanics; diplodocus; sauropod; dinosaur Together with the long legs, the long neck is a characteristic feature of the ostrich (Struthio came- lus). At rest and during locomotion, the neck is kept in a more or less vertical position. Major advantages of a vertical neck posture are a good overview of the surrounding area and a low force that is required for balancing the neck and the head. During feeding, the length of the neck enables the bird to reach the ground with the bill in a standing position. Various movements are performed by the neck. During feed- ing, the head is moved up and down several times a second by dorsoventral movements of the cranial section of the neck. To clean the plumage the neck can be flexed about 1808 backwards. Complex move- ments of the neck occur during activities like defense or mating (e.g., Grzimek, 1968). Balancing or moving the neck evokes stress along the neck (Baumel and Raikow, 1993; Proctor and Lynch, 1993). In a horizontally extended neck, static stress can be very high in comparison to the stress in a vertical posture, especially at the base of the neck. When the neck is in a low position, compressive forces act along the vertebral centra whereas tensile forces act in the epaxial muscles, tendons, and ligaments (for analyses of the forces acting in the extremely long necks of sauropod dinosaurs see, e.g., Preuschoft, 1976; Alexander, 1985, 1989, 1997; Christian, 2002a). In contrast to muscles, ligaments exert forces passively without energy expenditure. Ligaments, however, cannot generate forces actively, which means that they are not suitable for controlling movements. Liga- ments are useful as braces that constrain move- ments, for generating forces that counteract against gravity, or as a means for storing elastic energy. In the ostrich, there are two major liga- ments running along the dorsal side of the neck (Figs. 1 and 2). The first of these ligaments runs above the tips of the neural spines. Parts of this ligament are attached to the neural spines whereas other parts cross several intervertebral joints, especially in the cranial section of the neck. Contract grant sponsor: Deutsche Forschungsgemeinschaft (DFG). *Correspondence to: Andreas Christian, Biologie, Universita ¨t Flensburg, Auf dem Campus 1, 24943 Flensburg, Germany. E-mail: christian@uni-flensburg.de Published online 18 May 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jmor.10542 JOURNAL OF MORPHOLOGY 268:701–714 (2007) Ó 2007 WILEY-LISS, INC.