By David B. Weishampel
The Ornithopoda, one in every of 5 suborders in the Ornithischia, used to be initially proposed by way of Marsh in 1881 to incorporate these bipedal dinosaurs owning a predentary bone outfitted over the rostral finish of the mandibles. Ornithopods as well-known this present day may be additional characterised by way of reasonably lengthy facial skele plenty built with well-developed, frequently toothless premaxillae and average to giant exterior nares. Maxillary and dentary dentitions differ yet frequently encompass at the very least one substitute sequence underneath the sensible set; a few have many rows of successional enamel. the teeth morphology indicates ornithopods have been suc cessful herbivores yet, as can be mentioned, the correct way(s) during which ornitho pods chewed their nutrients, therefore lending vital information regarding their tro phic place, has now not been settled. Postcranially, ornithopods exhibit specializa tion for bipedality in hindlimb building and shortage well-developed protecting buildings on their flanks, again, and tail. The Ornithopoda can itself be divided into 5 households: Fabrosauridae, He terodontosauridae, Hypsilophodontidae, 19uanodontidae, and Hadrosauridae (subdivided into the subfamilies Hadrosaurinae and Lambeosaurinae). either fabrosaurids and heterodontosaurids, first recognized from the overdue Triassic and Early Jurassic of Argentina and South Africa, have been small animals differing in information of cranial, dental, and appendicular anatomy. Fabrosaurids are be lieved to symbolize the basal ornithopod inventory (Galton 1972, 1978; Thulborn 1970a, 1972). in the course of the Jurassic, ornithopods underwent significant radiations that integrated the medium- to large-sized Hypsilophodontidae and the big bodied Iguanodontidae, either one of which survived into the Cretaceous.
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Extra resources for Evolution of Jaw Mechanisms in Ornithopod Dinosaurs
It is the combined caudal margin of the jugal and the rostral part of the quadratojugal that marks the rostral rim of the fenestra. In the remaining ornithopods (iguanodontids and hadrosaurids), the jugalquadratojugal articulation is a simple lapping joint in which a facet on the medial face of the caudal process of the jugal receives the lateral surface of the rostral quadratojugal. The former bears horizontal striae, indicating a firm connection between the jugal and quadratojugal. Additionally, in I.
Orientation and size of the pre- and postquadratic processes of the squamosal, size and depth of the squamosal socket, and development of a caudal protuberance on the quadrate in this region vary among ornithopods. In fabrosaurids, the dorsal head of the quadrate is somewhat constricted (Fig. , cf. Lesothosaurus diagnosticus BMNH R8501). The postquadratic process is small and directed away from the caudal margin of the quadrate head. Morphologic details of the quadrate head come from an isolated quadrate belonging to L.
In a somewhat different fashion, the rostroventrallacrimal in hadrosaurids is overlapped by the dorsal margin of the maxillary process of the jugal, as well as by the adjacent dorsal maxilla (Fig. 7b-d). Caudally, the lacrimal sends a stout buttress to the jugal, the ventral surface of which is transversely concave and receives the adjacent convex caudal margin of the jugal (e. , Lambeosaurus lambei NMC 351, AMNH 5353, ROM 1218, Parasaurolophus tubicen PIUU R222, Hypacrosaurus altispinus NMC 2246, Corythosaurus casuarius ROM 871, NMC 8503, AMNH 5240, Edmontosaurus regalis CM 26258, UM 20000, BMNH R8927, Maiasaura peeblesorum PU 22405, Gilmoreosaurus mongoliensis AMNH 6551, Saurolophus osborni AMNH 5221).
Evolution of Jaw Mechanisms in Ornithopod Dinosaurs by David B. Weishampel