![]() A hinge is present between the premaxilla, upper part of the jaws, and braincase on the one side and the maxilla and bones of the cheek region on the other. Additionally, ornithopods have a more complex chewing (grinding of upper teeth against lower ones) than other dinosaurs. Most ornithopods have premaxillae with rugose (roughened) surfaces, at least some development of an olecranon process ("funny bone projection") of the ulna, and caudal neural spines which extend beyond their centrum. Given the uncertainty about their relationships and membership, there aren't any clear synapomorphies for the group. The latest studies (from 2020) have re-expanded Ornithopoda to include most of the classic "hypsilophodont"-grade (i.e., non-iguanodontian) ornithopods. So what IS an ornithopod, then? Ornithopoda is defined as Parasaurolophus and all taxa closer to it than to Triceratops. So small ornithischians show complex types of integument beyond scales (and beyond fuzz). It has some parts of its body (bottoms of the feet) there are simple scales on the front of the legs and on top of the tail are more plate-like scales on other parts of the body are simple filaments and then there are odd plates with fuzz coming off them (unlike any structure known in other dinosaurs). It is found in an environment which fine details can be preserved. More interesting than that, though, is its body covering. Firstly it was found in bonebeds of many dozens of individuals, so it is very likely it lived in groups. It is a noteworthy animal: not so much in terms of its skeleton (which is boringly standard for a neornithischian), but for its behavioral evidence and integument. Of currently uncertain position is early Middle Jurassic Siberian Kulindadromeus it might be a basal ornithopod, or a basal marginocephalian, or (as shown here) outside Cerapoda. The data from these fossils are helping to sort out the relationships of the bird-hipped dinosaurs.) A few studies from 2015 onward went further: they found thescelosaurids, jeholosaurids, and even Hypsilophodon itself (the classic non-iguanodontian ornithopod) as outside Ornithopoda! ![]() (The recognition of the non-ornithopod status of these Jurassic forms comes in great part with the discovery of Eocursor, " Stormbergia" (really, adult Lesothosaurus), and other Late Triassic/Early Jurassic ornithischians. (Cerapods are united by the shared presence of asymmetrical teeth with enamel on only one side, allowing them to be ever-sharpening.). So there are at present no recognized Late Triassic or Early Jurassic ornithopods.Įven more recently, Middle Jurassic taxa (such as Chinese Agilisaurus and Hexinlusaurus, and the Cretaceous ultra-long tailed Australian Leaellynasaura were found to be neornithischians outside of Ornithopoda plus Marginocephalia: the clade clade Cerapoda. More recently, however, heterodontosaurids have been recognized as splitting from other ornithischians at a very basal divergence, and thus are no closer to ornithopods than to marginocephalians or to thyreophorans. With the development of cladistic analysis, it was recognized that Scutellosaurus and Scelidosaurus belonged with the stegosaur-ankylosaur clade, and that Pisanosaurus and Lesothosaurus (both of which were originally called "fabrosaurs") were primitive ornithischians outside of all the other major groups.īut even at the dawn of the 21st Century, Heterodontosauridae was still generally considered as sharing a more recent common ancestor with the "hypsilophodonts" and iguanodontians than with any other group of dinosaur: thus, the heterodontosaurids were thought to be the oldest branch of Ornithopoda. Eventually, pachycephalosaurs were recognized as their own distinct clade, and psittacosaurids as ceratopsians. Traditionally, Ornithopoda ("bird feet") comprised all ornithischians that weren't stegosaurs, ankylosaurs, or neoceratopisans. Both major clades-hollow-crested Lambeosaurinae and broad-snouted Hadrosaurinae-show extensive features for some form of visual (and/or auditory) displays, suggested complex social interactions. These "duck-billed" dinosaurs are known from the entire life cycle, and from entire herds. ![]()
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