Over the years, there has been much speculation as to what the prosauropods actually fed on (Sect. 10.2). The subject has been reviewed by VanHeerden (1997) who presented a table (see Table 4) adapted from the work of P.M. Galton contrasting the features of the jaws and teeth of carnivorous and herbivorous reptiles past and present. When the articulation of the jaw is in line with the rows of teeth, as in carnivorous reptiles, the jaws close in a scissors-like manner. In con-
■ Table 4. Features of the jaws and teeth of herbivores and carnivorous reptiles. (Based on VanHeerden 1997)
Jaw articulation below the rows of teeth Teeth closely spaced
Tooth crowns twisted so that they overlap in side view Teeth leaf-shaped
Teeth have coarse serrations at about 45° to the edge of the crown that occur more towards the tips
Teeth are more or less the same size (because there is less breakage)
Jaw articulation in line with the rows of teeth Teeth with large gaps between them Tooth crowns in line along middle of the jaw
Teeth taper from root to tip
Teeth have fine serrations at right angles to the edge of the crown
Teeth are of different sizes. New teeth replace broken and lost ones trast, when the jaw articulation is offset vertically from the rows of teeth, the force of the bite is distributed over a greater distance and less force is applied at any one point. Widely spaced teeth are better for piercing; closely spaced teeth form a cutting edge. When teeth are set in line along the middle of the jaw, they are less likely to be broken by struggling prey than when their crowns are twisted. Moreover, leaf-shaped herbivorous teeth are weaker than are spiky, tapering teeth - which work like daggers and can easily be extracted from the body of the prey when the jaws are opened. Teeth with fine serrations can cut harder material, such as bone, than can teeth with coarse serrations.
Despite the fact that plant material tends to be more resistant than animal flesh, it is argued that, in general, herbivorous dinosaurs would have selected softer vegetation and avoided the woody parts. From this, it is clear that most, if not all, of the basal sauropodomorphs would have been poorly adapted to a carnivorous diet - as would all the herbivorous forms discussed in Chapter 10. The theropods were probably all more or less carnivorous, even the toothless forms described below (Sect. 11.3.1).
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