Image: Edmontosaurus jaw

Description: The mandible (lower jaw) of an Edmontosaurus at the Museum of the Rockies in Bozeman, Montana, seen from the inner side (i.e. from the tongue side). It is not clear where this specimen was collected. Edmontosaurs belong to the so-called duck-billed dinosaurs (hadrosaurs), and were exceptionally numerous in Latest Cretaceous times throughout upper North America. As herbivores, they ripped leaves and plants using their bills, and then, unlike reptiles usually do, chewed the leaves and stems extensively. This caused wear to their teeth, which ground down quickly. The teeth were not only lying next to each other but were also stacked one above the other within the jawbone to form vertical tooth rows. So there were quite a lot of teeth in one jaw and all the densely packed teeth together are referred to as ‘tooth battery’. In the jaw that is shown above, many unworn, keeled, diamond-shaped surfaces of the stacked teeth are visible. Furthermore, the teeth erupted in a way that there was more than one tooth functional in each vertical row: The teeth rotated during their lifetime around the long axis of the jaw so that a new tooth first reached the mouth cavity on the inner side of the jaw, yet before the older tooth or teeth, sitting closer to the cheek, were entirely worn down. The tooth wear acting on the surfaces of about one hundred functional teeth formed an inclined chewing surface on each tooth battery. In the image above the chewing or wear surface is not visible because in the mandible it faces toward the cheek, not toward the tongue (but see this image for comparison). Only the inner edge of the chewing surface, running along the top of the inner surface of the tooth battery, with the keels forming conspicious spikes, is discernible.
Title: Edmontosaurus jaw
Credit: Edmontosaurus jaw from above showing rows of inner teeth - Museum of the Rockies - 2013-07-08 Uploaded by FunkMonk
Author: Tim Evanson from Washington, D.C., United States of America
Usage Terms: Creative Commons Attribution-Share Alike 2.0
License: CC BY-SA 2.0
License Link: http://creativecommons.org/licenses/by-sa/2.0
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