Dinosaur Teeth Herbivorous and Carnivorous

People with cavity-bearing teeth pulled from their jaws or who have seen X-ray photographs of their teeth have the opportunity to observe a few or most of the tooth parts and their orientations. Teeth have two primary layers, tough enamel on the outside and softer dentine on the inside. The part of the tooth exposed above the gumline of an animal is its crown, whereas the part within the socket is the root. In many cases, the root composed the majority (as much as 75%) of a dinosaur tooth. The side of a tooth closest to the tongue is its lingual side, whereas the outer side is labial. Small protuberances, in some cases found on the apical (top) parts of the crowns, are denticles. Narrow places on teeth that form blades or ridges, typically on their anterior and posterior sides, are carinae.

Another detailed feature in teeth of some modern and ancient animals, but absent in humans, are serrations. These are square, triangular, oval, or rectangular denticles on carinae separated by narrow indentations (cellae) along a tooth surface. Serrations considerably increase the surface area of a tooth and can be described as coarse or fine, depending on the relative size of the denticles. Coarse serrations are useful for roughly cutting soft material, such as woody tissue. Fine serrations are more efficient at ripping through both soft and hard tissue, such as flesh and bone. Serrations also serve to temporarily hold the object being cut, especially if the serrations are angled with respect to the long-axis orientation of the tooth. The cutting motion is accomplished by pulling the serrated surface across the object. A motion in the opposite direction would encounter more resistance because of the angled serrations gripping the cut object. A smooth (non-serrated) blade applies its shearing force to a much smaller area and thus causes more stress, which cuts efficiently with either a pulling or pushing motion, but does not grip the cut object. The latter principle shows why some swords, such as those made in medieval Japan (katana or wakazashi) were designed with thin, smooth blades instead of serrations. In contrast, steak knives typically are designed with serrations so that they can grip a steak as it is being cut mainly with a pulling motion.

Dentition is the sum of a dinosaur's teeth in its jawbones, which consist of the dentary, maxillary, and in some cases the premaxillary. Dinosaur teeth were individually grown in sockets of the jawbones, which differs from teeth fused to those bones, seen in modern lizards. This socketing allowed for lost teeth to be replaced by teeth below the roots. The closing of a dinosaur mouth, so that the teeth from the upper and lower parts of the jaw came together, is called occlusion; where teeth come together is the occlusal surface. If the occlusion causes teeth from the maxillary or premaxillary to cover the teeth of the dentary and predentary, an overbite results, whereas the opposite condition is an underbite. Most dinosaurs had a noticeable overbite, especially theropods (Chapter 9). Occlusion could have varied as a result of any tooth injuries that broke or damaged a tooth.

In most dinosaurs, dentition was composed of individual teeth that were similarly shaped, with tooth shapes including teardrop-shaped, peg-like (cylindrical), conical, or bladed with diamond- or D-shaped cross-sections (Fig. 8.6). However, even if teeth were similarly shaped, the sizes of the teeth could have varied within the same jaw of a dinosaur. Heterodont dentition shows a variety of tooth shapes

FIGURE 8.6 General tooth shapes typically associated with certain clades of dinosaurs (but with some exceptions as noted in the text). (A) Leaf-like (prosauropods, ornithopods, thyreophorans). (B) Peg-like (sauropods). (C) Conical (some theropods).

FIGURE 8.6 General tooth shapes typically associated with certain clades of dinosaurs (but with some exceptions as noted in the text). (A) Leaf-like (prosauropods, ornithopods, thyreophorans). (B) Peg-like (sauropods). (C) Conical (some theropods).

Theropod Tooth

in a dinosaur's jaws, as is seen in the Eoraptor from the Late Triassic of Argentina (Chapter 6). This dentition is also a namesake feature of one clade of ornithopods, the Heterodontosauridae (Chapter 11). Another variation of teeth in some ornithopods and ceratopsians were dental batteries, in which the teeth in the cheek region were fused together to form compound teeth. The most complex dental batteries known are those of hadrosaurs, which had more than a hundred teeth in each battery (Chapter 11). Some ceratopsians (Chapter 13) had less numerous teeth but similar batteries. One analogy that may help with visualizing how the arrangement of teeth in a dental battery worked is to think of them as bricks in a wall. Individually they would have had little supportive strength for grinding food, but when cemented together they composed a formidable tool for increasing the surface area to grind tough plants. Dental batteries apparently developed just prior to the middle of the Cretaceous Period. Thus, they may indicate some evolutionary response to changing vegetation patterns during the Mesozoic Era.

A secondary characteristic that dinosaur teeth acquired during life were signs of wear. In most instances these wear marks were inflicted by a dinosaur's own teeth with normal occlusion during biting or chewing. These wear patterns provide valuable evidence of jaw mechanics for dinosaurs, indicating how certain dinosaur species chewed. In other cases, the teeth may have been damaged after encountering resistance from whatever object a dinosaur was biting. Worn and damaged teeth, as documented from the geologic record, bear testimony of dinosaur food preferences. For example, some paleontologists have proposed that a few carnivorous dinosaur species must have been scavengers because their teeth show little evidence of wear, suggesting that they may have fed only on soft, rotting flesh. In contrast, high incidences of worn and broken teeth may represent attempts at biting live, struggling prey or fracturing primarily compact (versus cancellous) bones. Although tooth hardness with respect to the bitten object is a factor, the role of jaw strength in tooth wear cannot be underestimated. For perspective, the biting force measured from some humans indicates that they could bite through a steel bar if their teeth were composed of diamond instead of dahllite. Indeed, some dinosaur toothmarks provide indirect evidence of their bite strength, clarifying why dinosaurs show numerous replacement teeth in their jaws. They should have lost their teeth on a frequent basis in correspondence with food choices and bite forces.

Herbivorous dinosaurs had teeth that were functional for grasping, tearing, shearing, and grinding plant material. The wide variation of tooth shapes in different herbivorous dinosaurs is an indirect indicator of the plant diversity consumed by these dinosaurs. In modern herbivorous reptiles, a model for comparison to presumed herbivorous dinosaurs, teeth are:

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    How to differ dinosaur teeth?
    8 years ago
  • aatifa
    Why are some dinosaurs teeth serrated?
    8 years ago
  • Jana
    Did herbivorous dinosaurs have teeth?
    7 years ago
  • aleksi
    How carnivorous dinosaurs fed?
    7 years ago

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