Dryosaurus (lat.: Dryosaurus) a genus of dinosaurs of the Upper Jurassic period from the infraorder Ornithopoda (Ornithopoda), which lived on the territory of modern North America. It belongs to the family Dryosaurids (lat.: Dryosauridae), which is a group of bipedal herbivorous dinosaurs of small to medium size.
The first dryosaurus fossils were found in western North America, in the Morrison Formation.: Morrison Formation), containing large deposits of fossil remains of prehistoric animals.
The only currently recognized species of this dinosaur is Dryosaurus altus, although earlier 2 more species were included in this genus, which were found in England and Tanzania. However, today they are classified as separate genera Dizalotosaurus (lat.: Dysalotosaurus) and Valdosaurus (Valdosaurus).
Anatomical features
Dryosaurus had a physique typical of dryosaurids. So, he had long hind limbs, and the tibia was longer than the femur.
Its front (upper) limbs were short and ended in five-fingered hands. The sacrum consisted of 6 fused sacral vertebrae, while the anterior and posterior parts of the pubic bone were long and thin.
Unlike members of the Hypsilophodontidae family (lat.: Hypsilophodontidae) its premaxilla, located in front of the upper jaw, was devoid of teeth. The jaws of the dryosaurus ended in a beak made of horny substance.
paleobiology
As part of a histological study of the found bone material, a group of American paleontologists led by John R. Horner (English).: John R. Horner studied the developmental patterns of this dinosaur and two other ornithopods. All the bones of the dryosaurus studied by these scientists belonged only to juvenile animals, since the remains of adults could not be found. Perhaps the growth of these dinosaurs stopped only at the age of 15.
In the smaller ornithopod orodromea (lat.: Orodromeus), on the contrary, the growth process was very much weakened already at the teenage stage of development. It is assumed that in these animals it completely stopped when they reached 4-6 years of age.
Based on their found remains, the researchers suggested that the body length of relatively young individuals of the dryosaurus was 2.5-4.3 m, and the weight was from 77 to 90 kg.
Classification
Dryosaurus is an eponymous (giving its name to a higher taxon) representative of the Dryosaurid family, which is part of the Iguanodont suborder (lat.: Iguanodontia). Its relationship to other dryosaurids is unclear.
For a long time, the dryosaurus was considered a member of the Hypsilophodontidae family (lat.: Hypsilophodontidae). And only in 1984, British researchers Angela Milner (Eng.: Angela Milner) and David Norman (David Norman) assigned this dinosaur to a separate family of Dryosaurids they identified to reflect its differences from hypsilophodontids.
In 1985 John Cooper.: John Cooper) introduced into the classification the now rejected subfamily Dryosaurines (lat.: Dryosaurinae), but at the same time included it in the family Hypsilophodontidae.
History of finds and names
The first dryosaurus specimen found includes 1 tooth, pelvis and bones of one hind limb (holotype specimen no. YPM 1876). It was found in the US state of Wyoming in the highlands of Como Bluff (Eng.: Como Bluff), in the Morrison Formation, known throughout the world as a graveyard of dinosaurs.
In 1878, the American Othniel (Othniel) Charles Marsh (eng.: Othniel Charles Marsh) originally described this find as a new species of the genus Laosaurus, Laosaurus altus. And only after the discovery of new fossils of this unknown species, in 1894, the scientist noticed its important differences from other types of Laosaurus, such as longer cervical vertebrae and a thinner front part of the pubic bone, and classified it as a representative of the independent genus Dryosaurus he identified.
Marsh used the Latin generic name “Dryosaurus” (from the Greek words “drys” “tree” and “sauros” “lizard”), that is, “arboreal lizard”, to emphasize that this animal was supposedly herbivorous and possibly lived in forests. In any case, the area of sedimentary deposits of the Morrison Formation, where the habitat of the Driosaur was located, he interpreted as a lush forest with freshwater lakes.
circa 1922 in Dinosaur National Park.: Dinosaur National Monument) in Utah managed to recover from the sedimentary rock almost a complete skeleton, including a crushed skull (specimen No. CM 3392). In 1925, the found bone material was described by Charles Whitney Gilmour (Eng.: Charles Whitney Gilmore. This skeleton is currently on display at the Carnegie Museum of Natural History in the Pittsburgh suburb of Oakland.
Subsequent copies of the fossils of the Driosaurus were found in particular in the Montrosa district, Colorado (there in 1973, many fragmentary remains of young animals were discovered), in the dinosaur cemetery, known as the “excavation of the bone hut” (English.: Bone Cabin Quarry, Wyoming, as well as Johnson County, also Wyoming, and Moffat County, Colorado.
