Othnielosaurus ("Othniel's lizard") was a hypsilophodont dinosaur that lived during the Late Jurassic period of North America and it was named in honor of the famous paleontologist Othniel Charles Marsh in 1878. It lived in the redwood forests of the Morrison Formation in Colorado and was previously under the names Laosaurus, Nanosaurus and Othnielia. Recently, the type specimen of Othnelia was deemed nondiagnostic, meaning the animal is now known as Othnielosaurus.
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), andpremaxillary 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 werecartilaginous 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.
O.C. Marsh named several species and genera in the late 19th century that have come to be recognized as hypsilophodonts or hypsilophodont-like animals, including Nanosaurus agilis (possibly), "N." rex, Laosaurus celer, L. consors, and L. gracilis. Thistaxonomy has become very complicated, with numerous attempts at revision in the years since. In 1877, Marsh named two species of Nanosaurus in separate publications, based on partial remains from the Morrison Formation ofGarden Park, Colorado. One paper described N. agilis, based on YPM 1913, with remains including impressions of a dentary, andpostcranial bits including an ilium, thigh bones, shin bones, and a fibula. The other paper named N. rex, a second species which Marsh based on YPM 1915 (also called 1925 in Galton, 2007), a complete thigh bone. He regarded both species as small ("fox-sized") animals. He assigned this genus to the now-abandoned family Nanosauridae. The next year, he named the new genus Laosaurus on material collected by Samuel Wendell Williston from Como Bluff, Wyoming. Two species were named: the type species L. celer, based on parts of eleven vertebrae (YPM 1875); and the "smaller" L. gracilis, originally based on a back vertebra's centrum, a caudal centrum, and part of an ulna (review by Peter Galton in 1983 finds the specimen to now consist of thirteen back and eight caudal centra, and portions of both hindlimbs). A third species, L. consors, was established by Marsh in 1894 for YPM 1882, which consists of most of one articulated skeleton and part of at least one other individual. The skull was only partially preserved, and the fact that the vertebrae were represented only by centra suggests a partially grown individual. Galton (1983) notes that much of the current mounted skeleton was restored in plaster, or had paint applied. These animals attracted little professional attention until the 1970s and 1980s, when Peter Galton reviewed many the "hypsilophodonts" in a series of papers. In 1973, he and Jim Jensen described a partial skeleton (BYU ESM 163 as of Galton, 2007) missing the head, hands, and tail as Nanosaurus (?) rex, which had been damaged by other collectors prior to description. By 1977, he had determined thatNanosaurus agilis was quite different from N. rex and the new skeleton, and coined Othnielia for N. rex. The 1977 reference, somewhat buried in a paper concerning the transcontinental species of Dryosaurus, did not elaborate, but did assign Laosaurus consors and L. gracilis to the new genus, and considered L. celer a nomen nudum. The publication of Drinker further complicated matters. Most recently, in 2007 Galton reevaluated Morrison Formation ornithischians and concluded that the femur on which "Nanosaurus" rex(and by extension Othnielia) is based is not diagnostic, and reassigned the BYU skeleton to Laosaurus consors, which is based on more diagnostic material. As the genus Laosaurus is also based on nondiagnostic material, he gave the species L. consors its own genus, Othnielosaurus. As a result, in practical terms, what had been thought of as Othnielia is now known as Othnielosaurus consors. Othnielia is not a synonym of Othnielosaurus, because they are based on different specimens; however, the skeletons that had been used to describe and depict Othnielia were reassigned to Othnielosaurus, leaving the older name with only the original femur. The current status for the various species is as follows: Nanosaurus agilis is a possible basal ornithopod, "N." rex (Othnielia) is a dubious basal ornithopod, Drinker nisti is its own tentatively valid taxon, L. consors is the type species for Othnielosaurus, and L. celer and L. gracilis are still considered dubious.
Othnielosaurus was one of the smaller members of the diverse Morrison Formation dinosaur fauna, diminutive in comparison to the giantsauropods. 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, Saurophaganax, Allosaurus, Ornitholestes, and Torvosaurus, the sauropods Apatosaurus, Brachiosaurus, Camarasaurus, Brontosaurus, 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 anomnivore. 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.
On the Media Edit
- Othnielosaurus is shown in the Walking With Dinosaurs Special: The Ballad of Big Al. However, it is referred to as Othnielia. It is targeted for prey by Big Al but as it is feeding near a Stegosaurus dinosaur, Al is unable to make his attack with being wounded by the Stegosaurus' lethal spikes.
- Othnielosaurus was seen in the novel version of Jurassic Park, under its' old name Othnielia. It lives side by side with its relative Dryosaurus in the Hypsilophodon Highlands. Before the InGen Incident, an Othnielosaurus got its neck stuck in between the branches of a tree where it died of suffocation. The park hosted a population of 23 Othnielosaurus. Othnielosaurus is portrayed as a half-arboreal herbivore, a view about the smaller ornithopods that has recently been disproved. Because the Othys spend so much time in the trees they were impossible to accurately track with the motion sensors. They're always jumping their fences. This explains why there are so much more Othys than expected. The expected population was 16, but there are 23. It apparently had a colour similar to that of the novel's Velociraptors, as when Tim saw a Velociraptor in the Othnielosaurus paddock, the adults thought he had mistaken an Othnielosaurus for a raptor. Later in the novel Muldoon states that the Othnielosaurus scavenged on the Hadrosaurus HD/09.
- In The Lost World novel, Ian Malcolm hears jumping in the jungle trees, and when the group thinks monkeys, Malcolm disagrees. It is probably Othnielosaurus hopping throughout the foliage.
- Othnielosaurus appears in Jurassic Park III: Park Builder, under its' old name Othnielia. It is nr. 75 of the Herbivore Ones.