Jaw Mechanics in Basal Ceratopsia (Ornithischia, Dinosauria)

Abstract

Ceratopsian dinosaurs were a dominant group of herbivores in Cretaceous terrestrial ecosystems. We hypothesize that an understanding of the feeding system will provide important insight into the evolutionary success of these animals. The mandibular mechanics of eight genera of basal ceratopsians was examined to understand the variability in shape of the jaws and the early evolution of the masticatory system in Ceratopsia. Data were collected on lever arms, cranial angles and tooth row lengths. The results indicate that psittacosaurids had higher leverage at the beak and in the rostral part of the tooth row than basal neoceratopsians, but lower leverage in the caudal part of the tooth row. Although the vertebrate mandible is generally considered as a third-class lever, that of basal neoceratopsians acted as a second-class lever at the caudal part of the tooth row, as is also true in ceratopsids. When total input force from the mandibular adductor muscles on both sides of the skull is considered, the largest bite force in basal ceratopsian tooth rows was exerted in the caudal part of the tooth row at the caudal extremity of the zone with near-maximum input force. Medially positioned teeth generate higher leverage than laterally positioned teeth. The largest bite force in all basal ceratopsians is smaller than the maximum input force, a limit imposed by the morphology of the basal ceratopsian masticatory system. In ceratopsids, caudal extension of the tooth row resulted in a much larger bite force, even exceeding the maximum input force. Anat Rec, 292:1352Rec, 292: -1369Rec, 292: , 2009. V V C 2009 Wiley-Liss, Inc.

The Functional and Palaeoecological Implications of Tooth Morphology and Wear for the Megaherbivorous Dinosaurs from the Dinosaur Park Formation (Upper Campanian) of Alberta, Canada

“…For this reason, many authors have envisioned ceratopsid jaws as having acted in a similar fashion, with the mandible rotating in an arcilineal fashion about the jaw joint to bring the teeth into occlusion [68], [70], [101]–[105]. However, the scissor analogy must not be taken too far because the jaw joint is offset ventrally from the tooth row, which would have constrained the teeth to occlude in a nearly parallel fashion [42].…”

Skull Ecomorphology of Megaherbivorous Dinosaurs from the Dinosaur Park Formation (Upper Campanian) of Alberta, Canada

“…Ankylosaurs are not strongly distinguished from either ceratopsids or hadrosaurids based on the distance between the jaw joint and coronoid process apex. This is somewhat surprising because both ceratopsids and hadrosaurids possess elevated coronoid processes and depressed jaw joints that are otherwise not developed to the same degree in ankylosaurs [84]–[86]. It may be that the ankylosaur coronoid apex is more rostrally displaced than in ceratopsids and hadrosaurids, resulting in subequal measurements of this variable.…”

“…Likewise, the rostral placement of the tooth row relative to the coronoid process in ankylosaurs means that they did not possess as powerful a bite as the other two taxa, in which the tooth row extends caudal to the coronoid process, resulting in increased leverage of the distal tooth row [84]–[86]. Other evidence cited in favour of a relatively weak bite in ankylosaurs is the presence of small, phyliform teeth with peg-like roots [92]–[94], and simple jaw musculature [95].…”

Feeding height stratification among the herbivorous dinosaurs from the Dinosaur Park Formation (upper Campanian) of Alberta, Canada

“…A common theme in the literature is the persistence of open-habitat cycadophytes (bennettitaleans and cycads) as forage for Late Cretaceous herbivores [34,97,108-113]. However, bennettitaleans went extinct by the Santonian [114], and cycads were probably absent from the DPF ([65,115,116], D. R. Braman, pers.…”