Bone Evidence

Figure 24: The differences between dinosaur bone and reptile bone. the top figure shows the bone of an endotherm that has many channels for blood vessels. The middle figure shows the bone of ectotherms which has few channels. The lower figure shows dinosaur bone which is like that of living endotherms in appearance.

In today's ecosystems, endotherms grow quickly. Birds grow the fastest (Ostriches may grow from egg to 150 pound bird in nine months). Ectotherms on the other hand grow very slowly. How can we measure the rate of growth of dinosaurs? An estimate of the growth rate can be estimated by studying the texture of the bone in thin section. Bones grow by the addition of crystals of mineral and the texture of the minerals may be examined. Dinosaur bone resembles mammal bones due to the presence of many tiny channels for blood vessels running through their bone. Both also contain Haversian canals which are long cylinders, pointed at both ends, where bone mineral had been dissolved and then redeposited in concentric layers. These Haversian canals are found in abundance in both mammals and dinosaurs but are quite rare in most reptiles. All dinosaurs show evidence of rapid growth rates. Bone consists of crystals of calcium phosphate and strands of collagen. When bone grows slowly, the collagen fibres are wrapped in layers resulting in densely packed crystals that are oriented in one direction. Dinosaur bone has a completely different texture due to rapid growth of the collagen fibers which are irregularly arranged.(Bakker, 1986)