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Significantly more is known about the foraging of ornithopods than other dinosaurs, primarily due to the fact that mummified remains, with stomach contents intact, have been found. It is known from the hadrosauid mummies that they ate twigs, berries and coarse plant matter, which correlates nicely with their size: ornithopods are thought to have been active foragers on ground cover and low-level foliage from conifers and in some cases deciduous shrubs and trees of the newly evolved anigosperms.

Although the exact oral mechanism differs among different ornithopods, the ornithopods generally had beaks in the front for cropping vegetation, the dental battery for shearing coarse plant matter, a large, robust coronoid process for well developed chewing muscles, as well as a tooth row that was deeply set in, indicating that large fleshy cheeks were present.

The first extensive study of ornithopod jaw mechanism was carried out by J.H. Ostrom in 1961, in which he concluded that the hadrosaurids chewed in propalinal (back to front) jaw movement on both sides of the mouth at the same time. This was confirmed by R.A. Thulborn, who claimed that chewing in heterodontosaurids as similar to what Ostrom suggested for hadrosaurids: bilateral proalinal jaw movement. However, other palaeontologists suggested otherwise, at least for different ornithopods such as in the case of Hypsilophodon, which may have chewed in much the same was as many mammals do today – side-to-side on one side of the mouth at a time as according to P.M. Galton.

More recently, studies by D.B. Norman, D.B. Weishampel, A.W. Crompton, and J. Attridge have been based not only on comparisons of ornithopod skulls and teeth, but also on computer analyses of cranial mobility, which showed yet another great variation. In the most primitive ornithopods, the very front of the cornified beak was relatively narrow and lacked teeth, suggesting a degree of selectivity in cropping ability. On the other hand, Iguanodontians have enlarged snouts, lost their front teeth and even developed a strongly serrate margin to their rhamphotheca, indicating that they were generalist; lacking selectivity in what they consume.

The heterodontosaurids chewed by combining vertical movement of the lower jaws with a slight degree of rotation of the mandible about their long axes, illustrated by their skull structure, patterns of tooth wear, and computer modeling. In this way, they were able to move their upper and lower teeth in a transverse direction and thus break up the bits of plant food that the tongue had placed between them. On the other hand, Euoronithopods evolved what Norman called pleurolinesis; mobilized their upper jaws to allow a slight rotation of the upper jaw, especially the maxilla relative to the snout and skull roof. When the upper and lower teeth were brought into contact on both sides, the upper jaws rotate laterally and the opposing surfaces of the teeth sheared past one another to break up plant food in the mouth.

As in all of the other ornithischians that have been discussed, once the food was properly chewed, it was swallowed and quickly passed into a capacious gut, which was present in all ornithopods and appears to have been relatively larger in the absolutely larger iguanodontians. Between the extensive chewing of food in the mouth and fermentation in the large gut, it is very likely that all ornithopods were well suited for a subsistence diet of low-quality, high-fiber vegetation.


Fastovsky, D.E. & Weishampel, D.B (2005) The Evolution and Extinction of the Dinosaurs(2nd Ed.), Cambridge University Press: Cambridge, UK.
Weishampel, D.B., Dodson, P., Osmolska, H. (2004).The Dinosauria (Ed.), University of California Press: California, US.



© 2008 Earth Sciences, University of Bristol