Temporal range: Early Jurassic, 190–188Ma
|Reconstruction of the skeleton|
Hammer & Hickerson, 1994
Hammer & Hickerson, 1994
Cryolophosaurus (// or //; "CRY-oh-loaf-oh-SAWR-us") was a large dilophosaurid theropod from the Early Jurassic. It possesed a crest on its head that, unlike other dilophosaurids, went across its head and looked strangely 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, formerly the upper Falla Formation, by paleontologist Dr. William Hammer in 1991. It was the first carnivorous dinosaur to be discovered in Antarctica and the first non-avian dinosaur from the continent to be officially named. Dated at 190 million years ago, from the Early Jurassic Period, it was originally described as the earliest known tetanuran, though subsequent studies have found that it is most likely a dilophosaurid.
The holotype FMNH PR1821 is the only known specimen of Cryolophosaurus. The specimen consists of a partial posterior skull, two maxillary fragments; nine maxillary teeth; both posterior mandibles; a fragmentary sixth cervical centrum; cervical vertebrae 7-10; several posterior cervical ribs; several anterior dorsal vertebrae; most mid and posterior dorsal vertebrae; several dorsal ribs; the fifth sacral vertebrae; three chevrons; many partial and complete caudal vertebrae and centra; two partial humeri; a proximal radius; a proximal ulna; a partial ilium; a proximal pubis; both ischia, but only one distal; two incomplete femora; the distal end of a tibia; the distal end of a fibula, and the astragalus and calcaneum. The specimen is not thought to be fully mature.
Cryolophosaurus was estimated as being 6 to 7 m (19.7 to 23.0 ft) in length and weighing approximately 460 kilograms (1,000 lb). Based on these length and weight estimates, Cryolophosaurus is the largest known Early Jurassic theropod. Smith et al. (2007) noted that this individual may represent a sub-adult.
The holotype of Cryolophosaurus consists of a high, narrow skull, which was discovered along with part of the rest of the skeleton. The skull is an estimates 65 centimetres (26 in) long. The peculiar nasal crest runs just over the eyes, where it rises up perpendicular to the skull and fans out. It is thin and highly furrowed, giving it a Spanish comb-like appearance. It is an extension of the skull bones, near the tear ducts, fused on either side to orbital horns which rise from the eye sockets. While other theropods like the Monolophosaurus have crests, they usually run along the skull instead of across it. The crest would have been ineffective as a weapon and may have possibly functioned as a display feature during certain types of social behavior such as mating.
A recent study has found that previous studies have lacked focus on endocranial details. The study found that Cryolophosaurus has a nearly complete, undistorted cranial cavity. The cavity is complete enough to give an approximate shape and size of the living brain. The endocast features clarified the dissimilarity of the skull with the endocast of Allosauroids and Coelurosaurs giving Cryolophosaurus a basal position in Theropoda.
Classification is difficult because Cryolophosaurus has a mix of primitive and advanced characteristics. The femur has traits of early theropods, while the skull resembles much later species of the clade Tetanurae, like China's Sinraptor and Yangchuanosaurus. This led Sereno et al. (1994) to place Cryolophosaurus in the taxon Allosauridae. 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, instead of being close to tetanurans. 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. The current scientific consensus is that Cryolophosaurus is a dilophosaurid, consistent with the Smith et al. (2007) conclusion.
Distinguishing anatomical features
A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism or group.
These distinguishing characters were identified by Smith et al. (2007b) in a description on the oseology of Cryolophosaurus:
- the presence of a large, anterodorsally curving midline crest on the top of the skull, with fluted rostral and caudal surfaces formed by dorsal expansions of the lacrimal bones;
- a complete constriction across the infratemporal fenestra formed by the squamosal and jugal;
- and the presence of extremely elongate cranial processes on the cervical ribs.
According to Smith, Makovicky, Pol, Hammer & Currie (2007), Cryolophosaurus can be distinguished based on the following cranial features:
- an anorbital fossa extending onto the lateroventral nasal side;
- nasolatcrimal crestsexpanding onto the anterior end of the jugal;
- a deep surangular;
- and a pendant medial process on the articular.
Cryolophosaurus can also be distinguished according to Smith et al. (2007) according to these postcranial features:
- amphicoelous cervical centra;
- a sigmoidal femus with an anteromedially directed head;
- and a low triangular astragalar ascending processes.
Discovery and naming
Cryolophosaurus was the first theropod to be discovered from Antarctica, but is was only the second dinosaur discovered. Cryolophosaurus was discovered after Antarctopelta, but even so, Antarctopelta was named later. It originally was collected during the 1990-91 austral summer on Mount Kirkpatrick in the Beardmore Glacier region of the Transantarctic Mountains. The discovery was made by William R. Hammer, a professor at the 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 State University 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 around the altitude of 4,000 m (13,000 ft) high and about 640 km (400 mi) from the South Pole. When the discovery was made, they soon notified Hammer. Over the next three weeks, Hammer excavated 2,300 kg (5,100 lb) of fossil-bearing rock. The team recovered over 100 fossil bones, including those of Cryolophosaurus. The specimens were formally named and described in 1994 by Hammer and William J. Hickerson, in the journal Science. 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 metres higher in the section on Mt. Kirkpatrick.
The name Cryolophosaurus ellioti is derived from the Greek words κρυος (meaning 'cold' or 'frozen'), λοφος (meaning 'crest') and σαυρος (meaning 'lizard'), thus "cold crest lizard". Hammer and Hickerson named the species C. ellioti, after David Elliot, who had made the initial discovery of the fossils.
Cranial display features, such as the one possessed by Cryolophosaurus, make sense in social, gregarious animals, where other members of the species are available to observe and interpret messages of sexual status. Padian, Horner and Dhaliwal (2004) challenged conventional hypotheses that that the purpose of bizarre cranial structures and post-cranial armor in dinosaurs, was either for attracting mates, intimidating/fighting rivals in the group, or intimidating potential predators of other species. Padian et al. noted that based on phylogenetic, histological, and functional evidence these bizarre structures can be explained by the phenomenon of intra-species recognition, which is supported by the fossil evidence.
When the type specimen was discovered, several long cervical ribs, of a prosauropod dinosaur were found in the mouth of Cryolophosaurus, which led Hammer (1998) to conclude that it was feeding on the prosauropod when it died. Hammer further noted that since the ribs were found extending all the way back to the theropod's neck region, this Cryolophosaurus individual may have choked to death these ribs. Smith et al. instead found that these remains belonged to the Cryolophosaurus specimen itself. Hammer also concluded that a post-canine tooth belonging to a tritylodont (an early mammal relative), found with the Cryolophosaurus remains, was part of its stomach contents when it died.
Some of the bones of Cryolophosaurus have pathologies that show evidence of scavenging. Broken teeth from at least two different theropods have also been found nearby.
Provenance and occurrence
All known specimens of Cryolophosaurus have been recovered in the Hanson Formation, which is one of only two major dinosaur-bearing rock formations found on the continent of Antarctica. It was discovered in 1990-1991 in "tuffaceous" siltstone deposited in the Pliensbachian stage of the Early Jurassic, approximately 182 to 190 million years ago. This geological formation is part of the Victoria Group of the Transantarctic Mountains, which is approximately 4,000 metres (13,000 ft) above sea level. The high altitude of this site supports the idea that early Jurassic Antarctica had forests populated by a diverse range of species, at least along the coast. Dinosaurs lived on all seven continents, but Antarctica was the last continent to produce dinosaur fossils. The Hanson Formation was deposited in an active volcano−tectonic rift system formed during the breakup of Gondwana.
Fauna and Habitat
In the Early Jurassic, Antarctica was closer to the equator and the world was considerably warmer than today, but 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 kilometres (400 mi) from the South Pole but, at the time it lived, this was about 1,000 km (621 mi) or so farther north. This formation has produced the remains of Glacialisaurus (a large basal sauropodomorph), a crow-sized pterosaur, a mammal-like reptile (a tritylodont, which is a type of synapsid about the size of a rat), herbivorous mammal-like reptiles, and another unknown theropod. In 2004, paleontologists discovered the partial remains of a large sauropod dinosaur that has not formally been described yet. There were also fossilized tree trunks recovered only two meters away from Cryolophosaurus, suggesting that plant matter had once grown on Antarctica's surface before it drifted southward.
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