Evolutionary Trends in the Jaw Adductor Mechanics of Ornithischian Dinosaurs

Abstract

Jaw mechanics in ornithischian dinosaurs have been widely studied for well over a century. Most of these studies, however, use only one or few taxa within a given ornithischian clade as a model for feeding mechanics across the entire clade. In this study, mandibular mechanical advantages among 52 ornithischian genera spanning all subclades are calculated using 2D lever arm methods. These lever arm calculations estimate the effect of jaw shape and difference in adductor muscle line of action on relative bite forces along the jaw. Results show major instances of overlap between taxa in tooth positions at which there was highest mechanical advantage. A relatively low bite force is seen across the tooth row among thyreophorans (e.g., stegosaurs and ankylosaurs), with variation among taxa. A convergent transition occurs from a more evenly distributed bite force along the jaw in basal ornithopods and basal marginocephalians to a strong distal bite force in hadrosaurids and ceratopsids, respectively. Accordingly, adductor muscle vector angles show repeated trends from a mid-range caudodorsal orientation in basal ornithischians to a decrease in vector angles indicating more caudally oriented jaw movements in derived taxa (e.g., derived thyreophorans, basal ornithopods, lambeosaurines, pachycephalosaurs, and derived ceratopsids). Analyses of hypothetical jaw morphologies were also performed, indicating that both the coronoid process and lowered jaw joint increase moment arm length therefore increasing mechanical advantage of the jaw apparatus. Adaptive trends in craniomandibular anatomy show that ornithischians evolved more complex feeding apparatuses within different clades as well as morphological convergences between clades. Anat Rec, 299:271-294, 2016. V C 2015 Wiley Periodicals, Inc.

Cranial Musculature in Herbivorous Dinosaurs: A Survey of Reconstructed Anatomical Diversity and Feeding Mechanisms

“…The incredible diversity of herbivorous dinosaur feeding mechanisms has been well documented through numerous studies ranging from those examining cranial osteology and dental microwear (e.g., Haas, 1955Haas, , 1963Haas, , 1969Ostrom, 1961Ostrom, , 1964Norman, 1984;Weishampel, 1984;Norman and Weishampel, 1985;Barrett and Upchurch, 1994;Calvo, 1994;Barrett, 2001;Rybczynski and Vickaryous, 2001;Varriale, 2011Varriale, , 2016Whitlock, 2011;Mallon and Anderson, 2014;Nabavizadeh, 2014;Nabavizadeh and Weishampel, 2016;Virág and } Osi, 2017) to those modeling the biomechanical performance of bite forces and cranial stresses in feeding, both two dimensionally (e.g., Ostrom, 1961Ostrom, , 1964Ostrom, , 1966Tanoue et al, 2009;Mallon and Anderson, 2015;Nabavizadeh, 2016) and three dimensionally (e.g., Rybczynski et al, 2008;Porro, 2009;Lautenschlager, 2013Lautenschlager, , 2015Lautenschlager, , 2017Button et al, 2014Button et al, , 2016Lautenschlager et al, 2016;Taylor et al, 2017). In order to accurately model cranial feeding mechanics, a detailed understanding of muscle architecture is required and, for this reason, muscle reconstruction is crucial.…”

Morphometry, Microstructure, and Wear Pattern of Neornithischian Dinosaur Teeth From the Upper Cretaceous Iharkút Locality (Hungary)

“…These assumptions were further strengthened by the observations of Nabavizadeh () on the craniomandibular system of numerous hadrosauroid specimens. According to Varriale (), Nabavizadeh (), as well as Nabavizadeh and Weishampel (), it now seems that mandibular long‐axis rotation, combined with an orthopalinal power stroke and accessory palinal movements, is a more viable model of the ornithopod jaw mechanism than pleurokinesis.…”

Linkage mechanisms in the vertebrate skull: Structure and function of three‐dimensional, parallel transmission systems

“…Biomechanical models link structure and function by providing quantitative hypotheses of how relevant morphological parameters relate to a particular biomechanical function (Herrel et al, 2002;Westneat, 2003;Van Wassenbergh et al, 2006;Davis et al, 2010;O'Brien and Bourke, 2015). In combination with comparative morphological datasets, such models can be used to identify patterns of functional evolution (Westneat, 1995;Wainwright et al, 2004;Nabavizadeh, 2016) or test the biomechanical hypotheses themselves (Bertram and Biewener, 1988;Druzinsky, 1993;Dumont et al, 2005;Ross et al, 2009;Soons et al, 2010). Mechanical linkages, interjointed chains of rigid links (Hartenberg and Denavit, 1964), provide a useful model for the motion and force transmission of musculoskeletal systems.…”