The species belongs to the allosauroids, a group of small to large-bodied, two-legged carnivorous dinosaurs that lived during the Jurassic and Cretaceous periods.Allosaurus jimmadseni, possesses several unique features, among them a short narrow skull with low facial crests extending from the horns in front of the eyes forward to the nose and a relatively narrow back of the skull with a flat surface to the bottom of the skull under the eyes. The skull was weaker with less of an overlapping field of vision than its younger cousinAllosaurus fragilis.Allosaurus jimmadsenievolved at least 5 million years earlier than fragilis, and was the most common and the top predator in its ecosystem. It had relatively long legs and tail, and long arms with three sharp claws. The nameAllosaurustranslates as "different reptile," and the second part, jimmadseni, honors Utah State Paleontologist James H. Madsen Jr.

Following an initial description by Othniel C. Marsh in 1877,Allosaurusquickly became the best known -- indeed the quintessential -- Jurassic theropod. The taxonomic composition of the genus has long been a debate over the past 130 years. Paleontologists argue that there are anywhere between one and 12 species ofAllosaurus在莫里森北美的形成。这个年代tudy recognizes only two species --A. fragilisandA. jimmadseni.

"Previously, paleontologists thought there was only one species ofAllosaurusin Jurassic North America, but this study shows there were two species -- the newly describedAllosaurus jimmadsenievolved at least 5 million years earlier than its younger cousin,Allosaurus fragilis," said co-lead author Mark Loewen, research associate at the Natural History Museum of Utah, and associate professor in the Department of Geology and Geophysics at the University of Utah led the study. "The skull ofAllosaurus jimmadseniis more lightly built than its later relativeAllosaurus fragilis, suggesting a different feeding behavior between the two."

George Engelmann of the University of Nebraska, Omaha initially discovered the initial skeleton of the new species within Dinosaur National Monument in 1990. In 1996, several years after the headless skeleton was collected, the radioactive skull belonging to the skeleton using a radiation detector by Ramal Jones of the University of Utah. Both skeleton and skull were excavated by teams from Dinosaur National Monument.

"Big Al," another specimen belonging to the new species, was discovered in Wyoming on United States Bureau of Land Management (BLM) land in 1991 and is housed in the collections of the Museum of The Rockies in Bozeman, Montana. Previously thought to belong toAllosaurus fragilis, "Big Al" was featured in the BBC's 2001 "Walking with Dinosaurs: Ballad of Big Al" video. Over the last 30 years, crews from various museums have collected and prepared materials of this new species. Other specimens include "Big Al Two" at the Saurier Museum Aathal in Switzerland andAllosaurusmaterial from the Dry Mesa Quarry of Colorado at Brigham Young University.

Early Morrison Formation dinosaurs were replaced by some of the most iconic dinosaurs of the Late Jurassic

Allosaurus jimmadseni住在半干旱莫里森floodpla形成ins of the interior of western North America. The older rocks of the Morrison Formation preserve a fauna of dinosaurs distinct from the iconic younger Morrison Formation faunas that includeAllosaurus fragilis, Diplodocus and Stegosaurus. Paleontologists have recently determined that specimens of this new species of dinosaur lived in several places throughout the western interior of North America (Utah, Colorado and Wyoming).

Study summary

Dinosaurs were the dominant members of terrestrial ecosystems during the Mesozoic. However, the pattern of evolution and turnover of ecosystems during the middle Mesozoic remains poorly understood. The authors report the discovery of the earliest member of the group of large-bodied allosauroids in the Morrison Formation ecosystem that was replaced byAllosaurus fragilis和说明的变化获得的属time. The study includes an in-depth description of every bone of the skull and comparisons with the cranial materials of other carnivorous dinosaurs. Finally, the study recognizes just two species ofAllosaurusin North America withAllosaurus fragilisreplacing its earlier relativeAllosaurus jimmadseni.

Fact sheet: Major points of the paper

• A remarkable new species of meat-eating dinosaur,Allosaurus jimmadseni, is described based on two spectacularly complete skeletons. The first specimen was unearthed in Dinosaur National Monument, in northeastern Utah.
• Allosaurus jimmadseniis distinguished by a number of unique features, including low crests running from above the eyes to the snout and a relatively narrow back of the skull with a flat surface to the bottom of the upper skull under the eyes. The skull was weaker with less of an overlapping field of vision than its younger cousinAllosaurus fragilis.
• At 155 million years old,Allosaurus jimmadseniis the geologically-oldest species of Allosaurus predating the more well-known State Fossil of UtahAllosaurus fragilis.
• Allosaurus jimmadseniwas the most common and the top predator in its ecosystem. It had relatively long legs and tail, and long arms with three sharp claws.

Study design

• Comparison of the bones with all other known allosauroid dinosaurs indicate that the species possessed unique features of the upper jaw and cheeks (maxilla and jugal) and a decorative crest stretching from just in front of the eyes to the nose.
• Many of the comparisons were made with the thousands of bones ofAllosaurus fragiliscollected from the famous Cleveland-Lloyd Dinosaur Quarry administered by the Bureau of Land Management that are housed in the collections of the Natural History Museum of Utah.
• On the basis of these features, the scientific team named it a new genus and species of dinosaur,Allosaurus jimmadseni(translating to "Jim Madsen's different reptile").
• Allosaurus jimmadseniis particularly notable for its slender, narrow skull with short sharp nasal crests compared to its close relative and successorAllosaurus fragilis.
• The study was funded in part by the University of Utah, the National Park Service and the National Science Foundation.

New dinosaur name:Allosaurus jimmadseni

• The first part of the name,Allosaurus, (a·luh·SAW·ruhs) can be translated from Greek as the "other," "strange" or "different" and "lizard" or "reptile" literally to "different reptile." The second part of the name jimmadseni (gym-MAD-sehn-eye) honors the late Utah State Paleontologist James Madsen Jr. who excavated and studied tens of thousands ofAllosaurusbones from the famous Cleveland-Lloyd Dinosaur Quarry in central Utah and contributed greatly to the knowledge ofAllosaurus.

Size

• Allosaurus jimmadseniwas approximately 26 to 29 feet (8-9 meters) long.
• Allosaurus jimmadseniweighed around 4000 lbs. (1.8 metric tonnes).

Relationships

• Allosaurus jimmadsenibelongs to a group of carnivorous dinosaurs called "allosauroids," the same group as the famousAllosaurus fragilis.
• Other dinosaurs found in rocks containingAllosaurus jimmadseniinclude the carnivorous theropods Torvosaurus and Ceratosaurus; the long-necked sauropods Haplocanthosaurus and Supersaurus; and the plate-backed stegosaur Hesperosaurus.
• Allosaurus jimmadseniis closely related to the State Fossil of Utah,Allosaurus fragilis.

Anatomy

• Allosaurus jimmadseniwas a two-legged carnivore, with long forelimbs and sharp, recurved claws that were likely used for grasping prey.
• Like other allosauroid dinosaurs,Allosaurus jimmadsenihad a large head full of 80 sharp teeth. It was also the most common carnivore in its ecosystem.

Age and geography

• Allosaurus jimmadsenilived during the Kimmeridgian stage of the Late Jurassic period, which spanned from approximately 157 million to 152 million years ago.
• Allosaurus jimmadsenilived in a semi-arid inland basin filled with floodplains, braided stream systems, lakes, and seasonal mudflats along the western interior of North America.
• Allosaurus jimmadsenirepresents the earliest species ofAllosaurusin the world.

Discovery

• Allosaurus jimmadsenican be found in a geologic unit known as the Salt Wash Member of the Morrison Formation and its equivalents exposed in Colorado, Wyoming, and Utah.
• The first specimen ofAllosaurus jimmadseniwas discovered in the National Park Service administered by Dinosaur National Monument in Uintah County, near Vernal, Utah.
• Allosaurus jimmadseniwas first discovered by George Engelmann of the University of Nebraska, Omaha on July 15, 1990 during a contracted paleontological inventory of the Morrison Formation of Dinosaur National Monument.
• Another specimen ofAllosaurus jimmadseniknown as "Big Al," was found on land administered by the U.S. Department of the Interior's Bureau of Land Management in Wyoming.
• Further specimens ofAllosaurus jimmadsenihave been subsequently recognized in the collections of various museums.
• Allosaurus jimmadsenispecimens are permanently housed in the collections of Dinosaur National Monument, Utah; the Museum of the Rockies, Bozeman, Montana; the Saurier Museum of Aathal, Switzerland; the South Dakota School of Mines, Rapid City, South Dakota; Brigham Young University's Museum of Paleontology, Provo, Utah; and the United States National Museum (Smithsonian) Washington D.C.
• These discoveries are the result of a continuing collaboration between the Natural History Museum of Utah, the National Park Service, and the Bureau of Land Management.

Excavation

• The first skeleton ofAllosaurus jimmadseniwas excavated during the summers of 1990 to 1994 by staff of the National Park Service's Dinosaur National Monument. The skeleton block was so heavy it required the use of explosives to remove surrounding rock and a helicopter to fly out the 2700 kg block. The head of the skeleton was missing
• The first bones ofAllosaurus jimmadsenidiscovered included toes and some tail vertebrae. Later excavation revealed most of an articulated skeleton missing the head and part of the tail.
• The radioactive skull of the first specimen ofAllosaurus jimmadseni, which had previously eluded discovery, was found in 1996 by Ramal Jones of the University of Utah using a radiation detector.

Preparation

• It required seven years to fully prepare all of the bones ofAllosaurus jimmadseni.
• Much of the preparation was done by then Dinosaur National Monument employees Scott Madsen and Ann Elder, with some assistance from Dinosaur National Monument volunteers and students at Brigham Young University.