Early Jurassic, 194–188Ma
|Replica of a reconstruction of the holotype skeleton, Brussels|
Hammer & Hickerson, 1994
Hammer & Hickerson, 1994
Cryolophosaurus (// or //; "CRY-oh-loaf-oh-SAWR-us") is a genus of large theropods including the single species Cryolophosaurus ellioti, known from the early Jurassic period of Antarctica. It was about 6 to 7 metres (20 to 23 ft) long and 460 kilograms (1,010 lb) in weight, making it one of the largest theropods of its time. Members of this species may have grown even larger, because the only known specimen probably represents a sub-adult.
C. ellioti possessed a distinctive crest on its head that spanned the head from side to side, similar to a Spanish comb. The shape of the crest has also been compared to a Pompadour hairstyle similar to the one famously worn by Elvis Presley, earning the species the nickname "Elvisaurus" before it was officially named. Based on evidence from related species and studies of bone texture, it is thought that this bizarre crest was used for intra-species recognition.
Cryolophosaurus is known from a skull, a femur and other material, the skull and femur of which have caused its classification to vary greatly. The femur possesses many primitive characteristics that have classified Cryolophosaurus as a dilophosaurid or a neotheropod outside of Dilophosauridae and Averostra, where as the skull has many advanced features, leading the genus to be considered a tetanuran, an abelisaurid, a ceratosaur and even an allosaurid. Currently, the consensus is that Cryolophosaurus is either a primitive member of the Tetanurae or a close relative of that group.
Cryolophosaurus was excavated from Antarctica's Early Jurassic, Sinemurian to Pliensbachian aged 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. The sediments in which its fossils were found have been dated at ~194 to 188 million years ago, representing the Early Jurassic Period.
All known specimens of Cryolophosaurus have come from one geological area, the Hanson Formation. Inside the Hanson Formation, Cryolophosaurus lived alongside Glacialisaurus (a large basal sauropodomorph), a dimorphodontid (a crow-sized pterosaur), a carnivorous tritylodont (a mammal-like reptile about the size of a rat), herbivorous mammal-like reptiles, and another unknown theropod.
Cryolophosaurus was a large, well-built theropod, one of the largest of its time. The genus has been described by Benson (2012) to clearly be a top predator in Antarctica. It had slender proportions. Cryolophosaurus was estimated as being 6 to 7 m (19.7 to 23.0 ft) in length, as said by Hammer & Hickerson, but in 2007 a revised length of 6.5 metres (21 ft) was found by Smith et al. 2007b. Weight estimates vary, from approximately 460 kilograms (1,010 lb) found by Benson et al. (2010), to 165 kilograms (364 lb), found by Smith et al. (2007b). Based on these length and weight estimates, Cryolophosaurus is currently the largest known Early Jurassic theropod. Smith et al. (2007b) and Benson (2012) noted that this individual probably represents a sub-adult, so adults could have been larger.
The holotype FMNH PR1821 is the only fully described 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. Recently, new material of Cryolophosaurus was unearthed in Antarctica. The description of this material has yet to be published in a non-abstract form.
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.
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 osteology 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 et al. (2007), Cryolophosaurus can be distinguished based on the following cranial and postcranial features: an antorbital fossa extending onto the lateroventral nasal side; nasolacrimal crests expanding onto the anterior end of the jugal; a deep surangular; a pendant medial process on the articular; amphicoelous cervical centra; a sigmoidal femur 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. Holtz (2010) found that based on evidence from related species and studies of bone texturethe bizarre crest was primarily for intra-species recognition.
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 Sinemurian to Pliensbachian stage of the Early Jurassic, approximately 194 to 188 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 dimorphodontid), 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 Judd Case and James Martin informally recovered the partial remains of a large sauropod dinosaur that has not formally been described yet. There were also remains of many plant genera recovered in the Early Jurassic Camp Hill Formation, around the same age as fossils of Cryolophosaurus, proving that dense plant matter had once grown on Antarctica's surface before it drifted southward.
- Holtz, T.R. Jr. (2012). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House Books for Young Readers. pp. 90–91. ISBN 978-0-375-82419-7.
- Hammer, W. R. & Hickerson, W. J. (1999). "Gondwana Dinosaurs from the Jurassic of Antarctica". In Tomida, Y.; Rich, T.H.; Vickers-Rich, Y. Proceedings of the Second Gondwana Dinosaur Symposium National Science Museum Monographs. 15: 211–217.
- Smith, Nathan D.; Makovicky, Peter J.; Hammer, William R.; and Currie, Philip J. (2007). "Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica and implications for early theropod evolution". Zoological Journal of the Linnean Society 151 (2): 377–421. doi:10.1111/j.1096-3642.2007.00325.x.
- Benson, R.J.; Brussatte, M. & Xu, X. (2012). Prehistoric Life. London: Dorling Kindersley. p. 259. ISBN 978-0-7566-9910-9.
- Meidlinger-Chin, V. (2013). "Braincase and Endocranial anatomy of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica". Geological Society of America Abstracts with Programs 45 (4): 65.
- Smith, N.D.; Hammer, W.R. & Makovicky, P.J. (2013). "New Dinosaurs from the Early Jurassic Hanson Formation of Antarctica, and Patterns of Diversity and Biogeography in Early Jurassic Sauropodomorphs". Geological Society of America Abstracts with Programs: 405–406.
- Smith, N. D.; Hammer, W. R.; Currie, P. (2005). "Osteology and phylogenetic relationships of Cryolophosaurus ellioti (Dinosauria: Theropoda): Implications for basal theropod evolution". Journal of Vertebrate Paleontology 25 (3): 116A–117A.
- Rich, T.R., Gangloff, R.A. & Hammer, W.R. (1997). Polar dinosaurs In: Currie, P.J. & Padian, K. (eds.). Encyclopedia of Dinosaurs. Academic Press. pp. 562–573. ISBN 978-0-12-226810-6.
- Sereno, P.C.; Wilson, J.A.; Larsson, H.C.E.; Dutheil, D.B. & Sues, H-D. (1994). "Early Cretaceous dinosaurs from the Sahara". Science. 266: 267–270.
- Hammer, W. R.; Hickerson, W. J. (1994). "A Crested Theropod Dinosaur from Antarctica". Science 264 (5160): 828–830. doi:10.1126/science.264.5160.828. PMID 17794724.
- Smith, N. D.; Makovicky, P.J.; Pol, D.; Hammer, W.R.; Currie, P.J. (2007). "The Dinosaurs of the Early Jurassic Hanson Formation of the Central Transantarctic Mountains: Phylogenetic Review and Synthesis". US Geological Survey Open-File Report 2007 (1047srp003). doi:10.3133/of2007-1047.srp003.
- Nesbitt, S. J.; Smith, N. D.; Irmis, R. B.; Turner, A. H.; Downs, A. & Norell, M.A. (2009). "A complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs". Science. 326: 1530–1533.
- Sues, H.D.; Nesbitt, S.J.; Berman, D.S. & Henrici, A.C. (2011). "A late-surviving basal theropod dinosaur from the latest Triassic of North America". Proceedings of the Royal Society B. 278 (1723): 3459–3464.
- Leslie, Mitch (December 2007). "The Strange Lives of Polar Dinosaurs". Smithsonian Magazine. Retrieved 2008-01-24.
- Dodson, P. (1997). Paleoecology In: Currie, P.J., & Padian, K. Encyclopedia of Dinosaurs. Academic Press. ISBN 978-0-12-226810-6.
- Glut, D.F. (2006). Dinosaurs, the Encyclopedia, Supplement 4. McFarland & Company, Inc. p. 749. ISBN 0-7864-2295-5.
- Padian, K.; Horner, J. R. & Dhaliwal, J. (2004). "Species recognition as the principal cause of bizarre structures in dinosaurs". Journal of Vertebrate Paleontology. 23 (3): 100A.
- Glut, D.F. (1999). Dinosaurs, the Encyclopedia, Supplement 1. McFarland & Company, Inc. p. 442. ISBN 978-0-7864-0591-6.
- Evans, D.C. & Vavrek, M.J. (2012). Ultimate Dinosaurs: Giants from Gondwana. Toronto:Royal Ontario Museum. pp. 30–1.
- Dodson, P. (1997). Distribution and Diversity. In: Currie, P.J. & Padian, K. Encyclopedia of Dinosaurs. Academic Press. pp. 10–13. ISBN 978-0-12-226810-6.
- Holtz, T.R., Jr., Molnar, R.E. & Currie, P.J. (2004). Basal Tetanurae; In: Weishampel, D.B.; Dodson, P. & Osmólska, H. (eds.). The Dinosauria. Second Edition. University of California Press. pp. 71–110. ISBN 0-520-24209-2.
- Pickrell, John (March 9, 2004). "Two New Dinosaurs Discovered in Antarctica". National Geographic. Retrieved 20 December 2013.
- Chandler, M.A.; Rind, D.; R. (1992). "Pangaean climate during the Early Jurassic: GCM simulations and the sedimentary record of paleoclimate". Geological Society of America Bulletin. 5 104: 543–559. doi:10.1130/0016-7606(1992)104<0543:PCDTEJ>2.3.CO;2.
- Smith, Nathan D.; and Pol, Diego (2007). "Anatomy of a basal sauropodomorph dinosaur from the Early Jurassic Hanson Formation of Antarctica" (pdf). Acta Palaeontologica Polonica 52 (4): 657–674.
- Rees, P.M. & Cleal, C.J. (2004). "Lower Jurassic floras from Hope Bay and Botany Bay, Antarctica". Special Papers in Paleontology. 72: 5–90.
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