The herbivorous sauropod dinosaurs of the Jurassic and Cretaceous periods were the largest terrestrial animals ever, surpassing the largest herbivorous mammals by an order of magnitude in body mass. Several evolutionary lineages among Sauropoda produced giants with body masses in excess of 50 metric tonnes by conservative estimates. With body mass increase driven by the selective advantages of large body size, animal lineages will increase in body size until they reach the limit determined by the interplay of bauplan, biology, and resource availability. There is no evidence, however, that resource availability and global physicochemical parameters were different enough in the Mesozoic to have led to sauropod gigantism.We review the biology of sauropod dinosaurs in detail and posit that sauropod gigantism was made possible by a specific combination of plesiomorphic characters (phylogenetic heritage) and evolutionary innovations at different levels which triggered a remarkable evolutionary cascade. Of these key innovations, the most important probably was the very long neck, the most conspicuous feature of the sauropod bauplan. Compared to other herbivores, the long neck allowed more efficient food uptake than in other large herbivores by covering a much larger feeding envelope and making food accessible that was out of the reach of other herbivores. Sauropods thus must have been able to take up more energy from their environment than other herbivores.The long neck, in turn, could only evolve because of the small head and the extensive pneumatization of the sauropod axial skeleton, lightening the neck. The small head was possible because food was ingested without mastication. Both mastication and a gastric mill would have limited food uptake rate. Scaling relationships between gastrointestinal tract size and basal metabolic rate (BMR) suggest that sauropods compensated for the lack of particle reduction with long retention times, even at high uptake rates.The extensive pneumatization of the axial skeleton resulted from the evolution of an avian-style respiratory system, presumably at the base of Saurischia. An avian-style respiratory system would also have lowered the cost of breathing, reduced specific gravity, and may have been important in removing excess body heat. Another crucial innovation inherited from basal dinosaurs was a high BMR. This is required for fueling the high growth rate necessary for a multi-tonne animal to survive to reproductive maturity.The retention of the plesiomorphic oviparous mode of reproduction appears to have been critical as well, allowing much faster population recovery than in megaherbivore mammals. Sauropods produced numerous but small offspring each season while land mammals show a negative correlation of reproductive output to body size. This permitted lower population densities in sauropods than in megaherbivore mammals but larger individuals.Our work on sauropod dinosaurs thus informs us about evolutionary limits to body size in other groups of herbivorous terrestrial tetrapo...

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 morphology and the function between different sections of the neck. Additionally, the function of major dorsal neck ligaments 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 examinations 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 dorsoventral and lateral directions but this part of the neck is usually kept straight at rest and during feeding. Dorsoventral 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 vertebrae. 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 ostrich, adopted different neck postures. The neck was probably kept very low during feeding. During interruptions of the feeding, e.g., in an alert, the head could have been lifted in an economic way by raising the cranial section of the neck. During standing and locomotion the head was probably located well above the shoulders.

The neck posture of Brachiosaurus brancai Janensch, 1914 is reanalysed by employing the Preuschoft method to deduce the pattern of stress in the joints between the vertebral centra along the neck. The cogency of different methods for reconstructing the posture of a long neck, especially the Preuschoft method and approaches that are based on optimal articulation of the neck vertebrae, is discussed critically. The results corroborate the reliability of the Preuschoft method whereas the analyses of recent vertebrates with long necks show that approaches based on optimal articulation of the neck vertebrae are less suited for reconstructing habitual postures of long necks during rest. Such models are better suited for reconstructing the neck posture that was employed during locomotion. With the evidence obtained by different methods a conclusive picture of the neck posture and the feeding strategy of Brachiosaurus brancai can be drawn. The neck appears to have been slightly S-shaped with a ventrally flexed cranial section, an approximately straight middle section, and a dorsally flexed proximal part. In the habitual posture during standing, the angle between the middle section of the neck and the horizontal plane was about 60 or 70. During locomotion the whole neck probably was kept in an lower position with the inclination reduced by approximately 20 compared with the position at rest. During feeding movements of the head relative to the neck and movements in the cranial neck section were performed without much altering the height of the centre of gravity of the neck. With slow dorsoventral movements of the whole neck pronounced changes in the feeding height were possible. Sideways movements of the whole neck were performed by lateral flexion at the base of the neck. According to these findings, the long neck of Brachiosaurus brancai was a means for browsing in great heights as well as a means for increasing the feeding volume without moving the body.

The mechanical laws which make possible several characteristic and well-known modes of primate locomotion are reviewed. Biological requirements are fulfilled in small and in large primates by utilizing different mechanical principles. On the basis of the mechanics, special morphological traits can be identified which are advantageous for performing these locomotor modes, and which determine different lifestyles. These morphological ‘adaptations’ consequently are different in larger and smaller primates. The divergence between large and small forms is clarified by the inclusion of non-primate mammals into the comparisons.

The lengths and diameters of the limb segments of 105 monitor lizards from 22 species were measured on preserved museum specimens in order to determine whether limb proportions vary in relation to snout-vent length (used as an indicator of overall body size). Scaling exponents (slopes of allometric equations) were estimated for log-transformed species' mean values, using both conventional nonphylogenetic statistics as well as the method of phylogenetically independent contrasts. Both methods gave essentially the same results. All limb segment lengths and diameters scale with exponents exceeding 1.0; thus, larger species of monitors tend to have larger limbs relative to their snout-vent length. Foot length, however, decreases relative to total hindlimb length in larger species. Measures of limb segment diameters scale with greater exponents than do limb lengths; thus, larger species also tend to have relatively thicker limbs. The empirical results on limb shape are consistent with predictions derived from biomechanical models.