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) |