FIGURE 5.4 Cranial bones in Allosaurus fragilis: compare with Figure 1.6.

bones are sutured tightly to one another and have no evidence of former movement. Others, such as the bones associated with the jaws, were capable of some rather complex movements (Chapters 9 to 13). Missing from this list of cranial bones is the postfrontal, which was present in ancestors of dinosaurs; its absence assists in their definition.

To invoke lukewarm responses from dinosaur paleontologists, tell them that you have found only teeth. Although teeth were part of the skull, in some areas they are commonly the only body fossils that remain of some dinosaur species, so their discovery seldom adds much to a paleontological survey. However, some teeth are distinctive enough to identify the presence of species that were previously unde-scribed. They also are extremely important for interpreting dinosaur paleobiology as they can be a guide to dinosaur dietary preferences, especially if the teeth can be matched to toothmarks (Chapter 14).

Teeth are preferentially preserved more often than other ossified tissues because they are typically composed of dense, compact bone (Chapter 8). Additionally, dinosaur teeth were in sockets (instead of being fused to the jaws, as in lizards), which caused them to pop out occasionally. These lost teeth were then continually replaced with new ones, which tended to bias the fossil record further. A problem with this abundance of dinosaur teeth in the fossil record is that teeth, because they are relatively smaller than many dinosaur bones and are composed of more durable material, have been more subject to reworking or transportation. So their occurrence in strata may not be in the same place or originated at the same time as the original dinosaur, making them suspect as guide fossils (Chapters 4 and 7).

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