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Chapter 3: Meet the Dinosaurs
The dinosaurs were a huge and varied group. This is reflected in their skeletons which show a variety of forms, from enormous frames that supported the largest animals ever to walk the Earth through to the delicate, elegant structures of the smallest dinosaurs. Despite such diversity of skeletal forms, there were many common themes that were replayed throughout their history.
SKELETAL DIVERSITY The secret of the dinosaurs' success lies partly in their design. Their legs were held directly under the body, allowing them to swing forward and backward and to avoid the sprawling gait characteristic of many other reptiles. A number of groups such as the theropods also had hallow bones that provided strength and support while keeping the animals' weight to a minimum. Sauropads also had weight-reducing adaptations in their skeletons. Despite, or, more properly, because of their immense size, their skeletons had to be as light as possible while still providing the strength needed to support their tremendous weight. The neck vertebrae, for example, had hallows and cavities with many of the processes reduced to struts. Edward Drinker Cope acknowledged this feature when he named CAMARASAURUS (box-lizard) after the hallow, box-like nature of this dinosaurs' neck vertebrae. There were also parts of the skeleton where structural strength was more important then weight-saving. Massive solid leg and arm bones held up by heavy bodies of sauropods, ceratopsians, stegosaurs, and ankylosaurs. Weight-bearing legs were held as straight as possible, improving their weight-carrying capacity. Armor, spikes, plates, and shields made of bone tended to make an animal heavy. It is no surprise that these features are found in dinosaurs that moved on all fours, where the extra weight could be distributed more evenly. In small dinosaurs, the emphasis was on flexibilty and agility. Small theropods and ornithipods had lightly built skeletons and a great deal of movement at the skeletal joints. They also tended to have very long legs for their size, indicating that they were fast runners able to duck and dive away from larger predators.