Post by Super Communist on Nov 4, 2011 20:48:07 GMT -5
Cryolophosaurus ( /ˌkraɪ.ɵˌlɒfɵˈsɔrəs/ or /kraɪˌɒlɵfəˈsɔrəs/; meaning "cold crest lizard") was a large theropod dinosaur, with a crest on its head that looked like a Spanish comb. Due to the resemblance of this feature to Elvis Presley's pompadour haircut from the 1950s, this dinosaur was at one point informally known as "Elvisaurus".
Cryolophosaurus was excavated from Antarctica's Early Jurassic (Pliensbachian stage) Hanson Formation (former the upper Falla Formation) by paleontologist Dr. William Hammer in 1991. It is the first carnivorous dinosaur to be discovered in Antarctica and the first dinosaur of any kind from the continent to be officially named (other than birds). Dating from the Early Jurassic Period, it was originally described as the earliest known tetanuran, though subsequent studies have found that it is probably a dilophosaurid. Nesbitt (et al., 2009) using the characters of Tawa found it to be a neither dilophosaurid nor averostran neotheropod but the sister group of a clade composed of dilophosaurids and averostrans.
Description
The holotype and only known individual of Cryolophosaurus is estimated as 6.5 metres (21 ft) long and weighing 465 kilograms (1,030 lb); this individual may represent a sub-adult and thus not fully grown, however.
A high, narrow skull was discovered, 65 centimeters (25 inches) long. The peculiar nasal crest runs just over the eyes, where it rises up perpendicular to the skull and fans out. It is furrowed, giving it a comb-like appearance. It is an extension of the skull bones, near the tear ducts, fused on either side to horns which rise from the eye sockets (orbital horns). While other theropods like the Monolophosaurus have crests, they usually run along the skull instead of across it.
Classification
"Cryolophosaurus is also of significance because it represents the oldest known tetanuran from any continent — it is the only one from the Early Jurassic."
—William R. Hammer
Classification is difficult because Cryolophosaurus has a mix of primitive and advanced characteristics. The leg bone (femur) has traits of early theropods, while the skull resembles much later species of the clade Tetanurae, like China's Sinraptor and Yangchuanosaurus. Originally, Hammer and colleagues suspected that Cryolophosaurus might be a ceratosaur or even an early abelisaur, with some traits convergent with those of more advanced tetanurans, but ultimately concluded that it was itself the earliest known member of the tetanuran group. While a subsequent study by Hammer (along with Smith and Currie) again recovered Cryolophosaurus as a tetanuran, a later (2007) study by the same authors found that it was more closely related to Dilophosaurus and Dracovenator than to tetanurans.
Discovery
Cryolophosaurus was originally collected during the 1990-91 austral summer on Mount Kirkpatrick in the Beardmore Glacier region of the Transantarctic Mountains, by William R. Hammer, professor at Augustana College, and his team. The fossils were found in the siliceous siltstone of the Hanson Formation (formerly the upper Falla Formation) and dated to the Pliensbachian stage of the early Jurassic.
In 1991, both Hammer and the Ohio geologist David Elliot had excavated separate outcroppings near Beardmore Glacier, sharing logistical expenses. Elliot's team first came across the remains of Cryolophosaurus in a rock formation (altitude 13,000 feet (4,000 m) and 400 miles (640 km) from the South Pole), and notified Hammer. Over the next three weeks, Hammer excavated 5,000 pounds (2300 kg) of fossil-bearing rock. The team recovered over 100 fossil bones, including those of Cryolophosaurus.
The remains included part of a partially-crushed skull, a jaw bone (mandible), parts of the backbone (30 vertebrae), hip bones (the ilium, ischium, and pubis), leg bones (femur and fibula), an ankle bone (tibiotarsus) and foot bones (metatarsals). These specimens were formally named and described in 1994 by Hammer and William J. Hickerson, in the journal Science. The name Cryolophosaurus ellioti was derived from the Greek κρυος (meaning 'cold' or 'frozen'), λοφος (meaning 'crest') and σαυρος (meaning 'lizard'). Hammer and Hickerson named the species C. ellioti after David Elliot, who had made the initial discovery of the fossils.
During the 2003 season, a field team returned and collected more material from the original site. In addition, a second locality was discovered about 30 meters higher in the section on Mt. Kirkpatrick.
Paleoecology
The remains of the Cryolophosaurus were found in the Hanson Formation with the remains of Glacialisaurus (a large basal sauropodomorph), a small pterosaur, a mammal-like reptile (a tritylodont, which is a type of synapsid about the size of a rat), and another unknown theropod. There were also fossilized tree trunks two meters away. The site is about 4,000 meters (13,000 feet) above sea level.
This supports the idea that, even at high altitudes, early Jurassic Antarctica had forests populated by a diverse range of species, at least along the coast. Even though Antarctica was closer to the equator and the world was considerably warmer than today, the climate was still cool temperate. Recent models of Jurassic air flow indicate that coastal areas probably never dropped much below freezing, although more extreme conditions existed inland. Cryolophosaurus was found about 650 kilometers (400 mi) from the South Pole but, at the time it lived, this was about 1,000 km (621 mi) or so farther north.
(Information taken directly from wikipedia)
