The Cranium

One of the easiest ways to attract the attention of dinosaur paleontologists is to announce that you have found a cranium, especially one of a sauropod (Chapter 10). Most dinosaur paleontologists want to find a dinosaur skeleton that is at least 90% complete, but skulls are relatively rare prizes that can be extremely meaningful for classification and interpretations of behavior. Because of the large number of bones in the cranium, which was attached to the anterior part of the axial skeleton through the articulation of the occipital condyle with the first cervical vertebra, it is one of the most complicated structures of a dinosaur.

Adjectives applied to common bones in a dinosaur skull are (in alphabetical order) the angular, basioccipital, basisphenoid, dentary, frontal, jugal, lachrymal, maxilla, nasal, parietal, palatine, premaxilla, postorbital, prefrontal, ptery-goid, quadrate, quadratojugal, surangular, squamosal, and vomer (Fig. 5.4). Keep in mind that many of these bones are paired, which nearly doubles the number of bones from this list. Openings in the skull are foramens, fenestrae (plural of fenestra), and orbits. Foramens and fenestrae are named after their proximity to the bones surrounding them (that is, the antorbital fenestra and surangular foramen), whereas orbits refer to the former positions of a dinosaur's eyes. The size of a dinosaur's orbit gives an approximation of the original size of its eyes, which, of course, is connected to hypotheses on dinosaur vision (Chapters 9 to 13). Most of the skull

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

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