Cryolophosaurus: Encyclopedia - Cryolophosaurus

Cryolophosaurus

Conservation status: Fossil

Cryolophosaurus ellioti (cry-oh-LOAF-oh-SORE-us, meaning "cold crested lizard") is a large bipedal dinosaur with a bizarre crest running across its head that looks like a Spanish comb. Due to the resemblance to Elvis Presley's pompadour haircut in the 1950s, the dinosaur is also informally known as the Elvisaurus.

Cryolophosaurus was discovered in Antarctica by the paleontologist 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. Dating from the early Jurassic, it is also the earliest tetanuran theropod yet discovered, though it is not the most primitive.

Cryolophosaurus - Description

Cryolophosaurus was about 6 to 8 meters (20 to 26 feet) long, which is significantly smaller than the largest Allosaurus, which reached up to 12 meters (40 feet) in length.

A high, narrow skull was discovered, which measures 65 centimeters (25 inches) in length. 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. The crest is actually an extension of the skull bones which lie near the tear ducts (the lachrymals), 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.

The crest is too fragile to be used in combat, so it was probably used in mating displays.

Cryolophosaurus - Forests of the night

The remains of the Cryolophosaurus were found with the remains of a very large prosauropod (related to plateosaurids like the Plateosaurus and Lufengosaurus), 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 a couple of meters away. The site is about 4,000 meters (13,000 feet) above sea level, and during the early Jurassic it was a riverbed on the southern coast of the supercontinent of Gondwana.

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 a cool temperate. Recent models of Jurassic air flow indicate that coastal areas probably never dropped much below freezing, though more extreme conditions existed inland. This suggests that dinosaurs can endure relatively cool environments, and even survive snow.

Cryolophosaurus was found about 650 kilometers (400 miles) from the South Pole, so it had to contend with the polar night. Since it is not currently believed that dinosaurs hibernated, or migrated en masse to more diurnal climes, Cryolophosaurus must have lived in the dark for months at a time.

The specimen was found in conjunction with a platter from the prosauropod which has led to speculation that it may have choked to death, though there is no concrete evidence of this one way or the other.

Cryolophosaurus - Classification

Classification is difficult because the 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 like China's Sinraptor and Yangchuanosaurus. Originally, it was suspected that the Cryolophosaurus might be a ceratosaur or even an early abelisaur with some traits convergent with those of more advanced tetanurans.

However, it is now believed to be an early tetanuran, specifically a carnosaur. It is not certain whether it is more closely related to the allosaurs or the sinoraptors. Any certain classification is difficult because early Jurassic dinosaurs are very rare. While Cryolophosaurus lived about 195 to 190 million years ago, its closest known relatives lived about 50 million years later.

A simplified possible evolutionary tree (cladogram):

• Theropoda (the misnamed "beast feet")
  • Tetanurae ("stiffened tails" and 3 fingers)
    • Carnosauria ("flesh eating lizards")
      • Cryolophosaurus
      • Allosauroidea
        • Sinraptoridae (like the Sinraptor and Yangchuanosaurus)
        • Allosauridae (like the Acrocanthosaurus and Allosaurus)

Cryolophosaurus - Discovery

Cryolophosaurus was discovered in 1991 by William R. Hammer and his team on Mount Kirkpatrick, the highest peak in the Queen Alexandra Range of the Transantarctic Mountains, and additional remains were excavated during a second expedition in 2003. They were located in the siltstone of the Falla Formation, and dated to the Pliensbachian age of the early Jurassic.

It was formally named and described in 1994 by William R. Hammer and William J. Hickerson, in the journal Science. The name Cryolophosaurus was dervived from the Greek kryos (meaning "cold" or "frozen"), lophos (meaning "crest") and sauros (meaning "lizard" or "reptile"). The name is a reference not to the extreme conditions faced by the excavation team, but to the relatively cool climate in which the dinosaur lived.

The remains include part of a skull (cranium), a jaw bone (mandible), parts of the backbone (30 vertebrae), hip bones (the illium, ischium, and pubis), leg bones (femur and fibula), an ankle bone (tibiotarsus), and foot bones (metatarsals). The skull was partially crushed by the Beardmore Glacier. At least the skull and jaw bone, and the foot bones, were found in their natural positions (articulated).

The 2003 expedition uncovered additional Cryolophosaurus remains which are awaiting preparation, and a possible skin impression.

Hammer is a professor of geology and paleontology at Augustana College in Rock Island, Illinois, and a curator at the Fryxell Geology Museum, where the holotype specimen currently resides.

Adapted from the Wikipedia article "Cryolophosaurus", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki