Othnielosaurus is a genus of ornithischian dinosaur that lived about 155 to 148 million years ago, during the Late Jurassic-age Morrison Formation of the western United States. It is named in honor of famed paleontologist Othniel Charles Marsh, and was formerly assigned to the genus Laosaurus. This genus was coined to hold fossils formerly included in Othnielia, which is based on remains that may be too sparse to hold a name; as such, it is part of decades of research to untangle the taxonomy left behind by Marsh and his rival Edward Drinker Cope from the Bone Wars. Othnielosaurus has usually been classified as a hypsilophodont, a type of generalized small bipedal herbivore or omnivore, although recent research has called this and the existence of a distinct group of hypsilophodonts into question.

 Othnielosaurus is known from material from all parts of the body, including two good skeletons, although the skull is still poorly known (note that earlier references use a multitude of names for this material, with most of them since 1977 using Othnielia rex). Othnielosaurus was a small animal, 2 meters (6.6 ft) or less in length and 10 kilograms (22 lb) or less in weight. It was a bipedal dinosaur with short forelimbs and long hindlimbs with large processes for muscle attachments. The hands were short and broad with short fingers. From the partial type skull and the skull on the possible specimen "Barbara", the head was small. It had small leaf-shaped cheek teeth (triangular and with small ridges and denticles lining the front and back edges), and premaxillary teeth with less ornamentation. Like several hypsilophodont or iguanodont-grade ornithopods such as Hypsilophodon, Thescelosaurus, and Talenkauen, Othnielosaurus had thin plates lying along the ribs. Called intercostal plates, these structures were cartilaginous in origin.

 Othnielosaurus (previously under the names Laosaurus, Nanosaurus, and Othnielia) has typically been regarded as a hypsilophodont ornithopod, a member of a nebulous and poorly defined group of small, running herbivorous dinosaurs. This was challenged by Robert Bakker et al. in 1990. In their description of the new taxon Drinker nisti, they split Othnielia into two species (O. rex and O. consors) and placed "othnieliids" as more basal than hypsilophodontids. With recent analyses suggesting a paraphyletic Hypsilophodontidae, the general idea of "othnielids" as basal to other hypsilophodonts has been supported, although Drinker has been controversial because virtually nothing new has been published on it since its description. Other basal ornithopods have sometimes been linked to Othnielosaurus, particularly Hexinlusaurus, considered by at least one author to be a species of "Othnielia", O. multidens. New studies concur with the hypothesis that Othnielosaurus is more basal than other traditional hypsilophodonts, but go even farther and remove the genus from Ornithopoda and the larger group Cerapoda, which also includes horned dinosaurs and domeheaded dinosaurs.

 Othnielosaurus was one of the smaller members of the diverse Morrison Formation dinosaur fauna, diminutive in comparison to the giant sauropods. The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons, and flat floodplains. Vegetation varied from river-lining gallery forests of conifers, tree ferns, and ferns, to fern savannas with rare trees. It has been a rich fossil hunting ground, holding fossils of green algae, fungi, mosses, horsetails, ferns, cycads, ginkgoes, and several families of conifers. Other fossils discovered include bivalves, snails, ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphans, several species of pterosaur, numerous dinosaur species, and early mammals such as docodonts, multituberculates, symmetrodonts, and triconodonts. Such dinosaurs as the theropods Ceratosaurus, Allosaurus, Ornitholestes, and Torvosaurus, the sauropods Apatosaurus, Brachiosaurus, Camarasaurus, and Diplodocus, and the ornithischians Camptosaurus, Dryosaurus, and Stegosaurus are known from the Morrison. Othnielosaurus is present in stratigraphic zones 2-5.

 Typically, Othnielosaurus has been interpreted like other hypsilophodonts as a small, swift herbivore, although Bakker (1986) interpreted the possibly related Nanosaurus as an omnivore. This idea has had some unofficial support, but little in the formal literature; description of more complete skull remains will be needed to test this hypothesis.

 Гофониилозавр — род птицетазовых динозавров, который жил около 155—148 миллионов лет назад, во времена позднего Юрского периода на территории формации Моррисон, в современной западной части Соединённых Штатов. Он назван в честь знаменитого палеонтолога Гофониила Чарльза Марша и первоначально был отнесён к роду лаозавров. Это название было придумано для окаменелостей, первоначально отнесённых к роду Othnielia, которых было слишком малое количество, чтобы давать им отдельное имя; ныне этот момент является предметом многолетних исследований по уточнению таксономии, составленной Маршем и его соперником Эдвардом Дринкером Копом во время так называемых Костяных войн.

 Гофониилозавр, как правило, классифицируется как гипсилофодонтид, член семейства небольших бипедальных всеядных динозавров, хотя последние исследования ставят под сомнение существование гипсилофодонтид как отдельного семейства.

 Гипсилофодонтиды (Hypsilophodontidae) — небольшие динозавры из группы орнитоподов, известны из Азии, Австралии, Европы, Северной Америки и Южной Америки, из пород со средней юры до позднего мелового периода. Рассматриваются как быстрые, двуногие, растительноядные, около 1—2 метров длиной. Группа традиционно включает почти всех двуногих птицетазовых динозавров, кроме игуанодонтов.

 Некоторые ранние филогенетические анализы определили, что это была естественная группа, но последние исследования показали, что группа в основном является парафилетической.

 Гипотеза о парафилетичности группы, т. н. «естественные гипсилофодонтиды» была выдвинута во второй половине 1990-x годов. В настоящее время гипсилофодонты традиционно описывается как парафилетическая группа находящаяся между Agilisaurus или Hexinlusaurus и Hypsilophodon или Gasparinisaura.

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Tags: Вымершие рептилии, Юра, авеметатарзалии, архозавроморфы, архозавры, гипсилофодонтиды, диапсиды, динозавроморфы, динозавры, неорнитискии, орнитоподы, птицетазовые, цераподы

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