Horner & Weishampel, 1988
Horner & Weishampel, 1988
The remains of Orodromeus were discovered by Robert Makela during the excavation in Teton County, Montana, of the Egg Mountain brooding colony of a much larger relative, Maiasaura. The type species, Orodromeus makelai, was named and shortly described by Jack Horner and David B. Weishampel in 1988. The generic name is derived from Greek ὄρος, oros, "mountain", in reference to the Egg Mountain site, and δρομεύς, dromeus, "runner", referring to the cursorial habits of the animal. The specific name honoured the late Makela.
The holotype specimen, MOR 294, was found in a layer of the Two Medicine Formation, dating from the Campanian stage, about 75 million years ago. It consists of a partial skeleton with skull. The paratypes are MOR 246, a clutch of nineteen eggs, some with embryo; PP 22412, a set of hindlimbs; MOR 331, a partial skeleton; MOR 248, a skeleton with skull; and MOR 403, a braincase. A full published description is still lacking, though an unpublished thesis on Orodromeus exists. However, MOR 246 and other eggs from Egg Mountain are now considered to belong to a troodontid which may be Stenonychosaurus.
In 1990, the species Laosaurus minimus, described by Charles Gilmore in 1909 based on NMC 9438, a partial left hindlimb and pieces of vertebra from the Oldman Formation in Alberta, was noted as possibly being Orodromeus. The fragmentary nature of the remains, however, make it difficult to assign the specimen with certainty.
Orodromeus is distinguished by a palpebral that is at its back attached to the postorbital; a boss on the jugal; a non-fused wrist; and triangular maxillary and dentary teeth with a vertical occlusion.
Orodromeus was by Horner & Weishampel assigned to the Hypsilophodontidae, as the youngest known member. Today these are seen as an unnatural, paraphyletic, group, and Orodromeus is simply considered to be a basal member of the Euornithopoda. Brown et al. (2013) put it in the family Thescelosauridae and named a new subfamily (Orodrominae) after it.
Because of the advanced development of the bones and teeth of the embryos, Horner concluded that the young of Orodromeus were precocial, in contrast to those of Maiasaura that would have been altricial.
Mallon et al. (2013) examined herbivore coexistence on the island continent of Laramidia, during the Late Cretaceous. It was concluded that small ornithischians like Orodromeus were generally restricted to feeding on vegetation at, or below the height of 1 meter.
Albertadromeus is an extinct genus of orodromine parksosaurid dinosaur known from the upper part of the Late Cretaceous Oldman Formation (middle Campanian stage) of Alberta, Canada. It contains a single species, Albertadromeus syntarsus.Averostra
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Changchunsaurus
Changchunsaurus (meaning "Changchun lizard") is an extinct genus of small herbivorous parksosaurid dinosaur from Early Cretaceous deposits of Gongzhuling, Jilin, China. It is the first named dinosaur genus from Jilin.Jeholosaurus
Jeholosaurus is a genus of ornithischian dinosaur from the Early Cretaceous Period. It is thought to have been a herbivorous small ornithopod.Jingshanosaurus
Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.Koreanosaurus
Koreanosaurus (meaning "Korean lizard") is a genus of ornithopod dinosaur. One species has been described, Koreanosaurus boseongensis.Laosaurus
Laosaurus (meaning "stone or fossil lizard") is a genus of neornithischian dinosaur. The type species is Laosaurus celer, first described by O.C. Marsh in 1878 from remains from the Oxfordian-Tithonian-age Upper Jurassic Morrison Formation of Wyoming. The validity of this genus is doubtful because it is based on fragmentary fossils. A second species from the Morrison Formation, L. gracilis, and a species from the late Cretaceous of Alberta, Laosaurus minimus, are also considered dubious.Neornithischia
Neornithischia ("new ornithischians") is a clade of the dinosaur order Ornithischia. They are the sister group of the Thyreophora within the clade Genasauria. Neornithischians are united by having a thicker layer of asymmetrical enamel on the inside of their lower teeth. The teeth wore unevenly with chewing and developed sharp ridges that allowed neornithischians to break down tougher plant food than other dinosaurs. Neornithischians include a variety of basal forms historically known as "hypsilophodonts", including the Parksosauridae; in addition, there are derived forms classified in the groups Marginocephalia and Ornithopoda. The former includes clades Pachycephalosauria and Ceratopsia, while the latter typically includes Hypsilophodon and the more derived Iguanodontia.Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Orodrominae
Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.Oryctodromeus
Oryctodromeus (meaning "digging runner") was a genus of small parksosaurid dinosaur. Fossils are known from the middle Cretaceous Blackleaf Formation of southwestern Montana and the Wayan Formation of southeastern Idaho, USA, both of the Cenomanian stage, roughly 95 million years ago. A member of the small, presumably fast-running herbivorous family Parksosauridae, Oryctodromeus is the first dinosaur published that shows evidence of burrowing behavior.Parksosauridae
Parksosauridae is a clade or family of small ornithischians which have previously been generally allied to hypsilophodontids. Parksosauridae is often considered a synonym of Thescelosauridae, but the two groups cannot be synonyms because Parksosauridae is defined as a stem, while Thescelosauridae is defined as a node.Parksosaurus
Parksosaurus (meaning "William Parks's lizard") is a genus of hypsilophodont ornithopod dinosaur from the early Maastrichtian-age Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada. It is based on most of a partially articulated skeleton and partial skull, showing it to have been a small, bipedal, herbivorous dinosaur. It is one of the few described non-hadrosaurid ornithopods from the end of the Cretaceous in North America, existing around 70 million years ago.Thescelosaurinae
Thescelosaurinae is a subfamily of ornithischian dinosaurs from the Early Cretaceous of Asia and the Late Cretaceous of North America.Thescelosaurus
Thescelosaurus ( THESS-il-ə-SOR-əs; ancient Greek θέσκελος-/theskelos- meaning "godlike", "marvelous", or "wondrous" and σαυρος/sauros "lizard") was a genus of small ornithopod dinosaur that appeared at the very end of the Late Cretaceous period in North America. It was a member of the last dinosaurian fauna before the Cretaceous–Paleogene extinction event around 66 million years ago. The preservation and completeness of many of its specimens indicate that it may have preferred to live near streams.
This bipedal ornithopod is known from several partial skeletons and skulls that indicate it grew to between 2.5 and 4.0 meters (8.2 to 13.1 ft) in length on average. It had sturdy hind limbs, small wide hands, and a head with an elongate pointed snout. The form of the teeth and jaws suggest a primarily herbivorous animal. This genus of dinosaur is regarded as a specialized basal ornithopod, traditionally described as a hypsilophodont, but more recently recognized as distinct from Hypsilophodon. Several species have been suggested for this genus. Three currently are recognized as valid: the type species T. neglectus, T. garbanii and T. assiniboiensis.
The genus attracted media attention in 2000, when a specimen unearthed in 1993 in South Dakota, United States, was interpreted as including a fossilized heart. There was much discussion over whether the remains were of a heart. Many scientists now doubt the identification of the object and the implications of such an identification.Zephyrosaurus
Zephyrosaurus (meaning "westward wind lizard") is a genus of orodromine ornithischian dinosaur. It is based on a partial skull and postcranial fragments discovered in the Aptian-Albian-age Lower Cretaceous Cloverly Formation of Carbon County, Montana, USA. New remains are under description, and tracks from Maryland and Virginia, also in the USA, have been attributed to animals similar to Zephyrosarus.