Cryolophosaurus

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Cryolophosaurus
Temporal range: Early Jurassic (Pliensbachian), 186–182  Ma
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Cryolophosaurus skeleton.jpg
Reconstructed skeleton, Field Museum of Natural History
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Eusaurischia
Clade: Theropoda
Clade: Neotheropoda
Genus:† Cryolophosaurus
Hammer & Hickerson, 1994
Type species
†Cryolophosaurus ellioti
Hammer & Hickerson, 1994

Cryolophosaurus ( /ˌkraɪəˌloʊfəˈsɔːrəs/ or /kraɪˌɒləfəˈsɔːrəs/ ; KRY-ə-LOH-fə-SAWR-əs) is a genus of large theropod dinosaur known from only a single species Cryolophosaurus ellioti, from the early Jurassic of Antarctica. It was one of the largest theropods of the Early Jurassic, with the subadult being estimated to have reached 6–7 metres (20–23 ft) long and weighed 350–465 kilograms (772–1,025 lb).

Cryolophosaurus was first excavated from Antarctica's Early Jurassic, 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 ~196 to 188 million years ago, representing the Early Jurassic Period.

Cryolophosaurus is known from a skull, a femur and other material, all 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, whereas the skull has many advanced features, leading the genus to be considered a tetanuran, an abelisaurid, a ceratosaur and even an allosaurid. [2] [3] Cryolophosaurus is currently considered to be a derived neotheropod, close to Averostra. Additionally, Cryolophosaurus possessed a distinctive "pompadour" crest that spanned the head from side to side. Based on evidence from related species and studies of bone texture, it is thought that this bizarre crest was used for intra-species recognition. The brain of Cryolophosaurus was also more primitive than those of other theropods.

Discovery and naming

Map showing location of the Mount Kirkpatrick dinosaur site, with stratigraphic context on the right Mount Kirkpatrick dinosaur site.jpg
Map showing location of the Mount Kirkpatrick dinosaur site, with stratigraphic context on the right

Cryolophosaurus 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 Hammer, a 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. Cryolophosaurus was the second dinosaur, and first theropod, to be discovered in Antarctica. It was discovered after Antarctopelta , but named earlier. [4]

In 1991, both Hammer and the Ohio State University geologist David Elliot excavated separate outcrops 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. [4] The specimens were formally named and described in 1994 by Hammer and Hickerson, in the journal Science . [4]

During the 2003 season, a field team returned and collected more material from the original site. A second locality was discovered about 30 metres (98 ft) higher in the section on Mt. Kirkpatrick. [5]

The name Cryolophosaurus ellioti is derived from the Greek words κρυος (meaning 'cold' or 'frozen', in reference to its discovery in Antarctica), 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. [4]

Description

Size comparison Cryolophosaurus Reflective Size Chart.svg
Size comparison

Cryolophosaurus was a large, well-built theropod, one of the largest of its time. The holotype specimen is estimated to have reached 6–7 m (20–23 ft) long and weighed 350–465 kg (772–1,025 lb). [6] [7] [8] In 2016 Molina-Pérez and Larramendi gave a larger estimation of 7.7 meters (25.3 ft) and 780 kg (1,720 lb). [9] Some researchers noted that the holotype individual probably represents a sub-adult, so adults could have been larger. [7] [10] Despite having slender proportions, Cryolophosaurus is one of the largest known Early Jurassic theropods. [10] [11]

The holotype FMNH PR1821 is the only fully described specimen of Cryolophosaurus. The specimen consists of an incomplete skull and mandibles lacking most of their front half; nine maxillary teeth; 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. [7] In 2013, new material of Cryolophosaurus was unearthed in Antarctica. The description of this material has not yet been published in a non-abstract form. [12]

Skull

Life restoration Cryolophosaurus reconstruction (flipped).jpg
Life restoration

The holotype of Cryolophosaurus consists of a high, narrow skull, which was discovered articulated with the rest of the skeleton. [6] The skull is an estimated 65 centimetres (26 in) long. It has a peculiar nasal crest that runs just over the eyes, where it rises perpendicular to the skull and fans out. It is thin and highly furrowed, giving it a unique "pompadour" appearance and earned it the nickname "Elvis aurus." [13] The crest 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. [14]

An unpublished study conducted by Vernon Meidlinger-Chin in 2013 suggested that previous studies lacked focus on endocranial details. The study found that the Cryolophosaurus fossil has a nearly complete, undistorted cranial cavity which is complete enough to give an approximate shape and size of the living brain. The endocast features clarified the dissimilarity of the skull with those of Allosauroids and Coelurosaurs giving Cryolophosaurus a basal position in Theropoda. [11] Closer examination of how the skull bones fused reviewed details in the snout and forehead that are exceptionally similar to Dilophosaurus . [15]

Classification

The unrestored holotype skull, FMNH PR1821. Cryolophosaurus Holotype Skull FMNH.jpg
The unrestored holotype skull, FMNH PR1821.
Fossil pelvis of Cryolophosaurus. The loop at the widest part of the pubis is large compared to later theropods. Cryolophosaurus Hip Fossil.jpg
Fossil pelvis of Cryolophosaurus. The loop at the widest part of the pubis is large compared to later theropods.

Classification of Cryolophosaurus is difficult because it has a mix of primitive and advanced characteristics. [16] 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 Paul Sereno et al. (1994) to place Cryolophosaurus in the taxon Allosauridae. [17] 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. [4] 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 . [14] [18] Sterling Nesbitt et al. (2009), using the characters of Tawa found Cryolophosaurus to be neither a dilophosaurid nor averostran neotheropod but instead the sister group of a clade composed of dilophosaurids and averostrans. [19] However, in 2012, Matthew Carrano found that Cryolophosaurus was a tetanuran, related to Sinosaurus , but unrelated to Dilophosaurus. [20] In 2020, a monograph of Dilophosaurus found Cryolophosaurus to be a derived neotheropod, close to Averostra, in a more derived position than Zupaysaurus , but less than Dilophosaurus. [21]

The following cladogram illustrates a synthesis of the relationships of the early theropod groups compiled by Hendrickx et al. in 2015. [22]

Neotheropoda
Restoration of a Cryolophosaurus in its environment CryolophosaurusDB.jpg
Restoration of a Cryolophosaurus in its environment

However, a 2020, a study conducted Adam Marsh and Timothy Rowe found Cryolophosaurus to be a basal Neotheropod. While it was still closer to Averostra than Coelophysoidea was, it was still more basal than Dilophosaurus. [23]

Neotheropoda
Coelophysoidea

Lepidus

Liliensternus

Coelophysis? kayentakatae

Coelophysis

Megapnosaurus

Camposaurus

Zupaysaurus

Cryolophosaurus

Dilophosaurus

Averostra

Ceratosauria

Tetanurae

Paleobiology

Cranial ornamentation

Reconstructed skull Cryolophosaurus ellioti skull (FMNH PR1821).jpg
Reconstructed skull

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. [24] Kevin Padian et al. (2004) challenged conventional hypotheses 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. [25] [26] Thomas R. Holtz Jr. (2010) found that the bizarre crest of Cryolophosaurus was primarily for intra-species recognition, based on evidence from related species and studies of bone texture. [27] According to Thomas Rich and his colleagues, 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. [28] In 2019, a species recognition function was disputed but a socio-sexual display structure model was suggested. [29]

Diet

When the type specimen was discovered, several long cervical ribs, of a supposed 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 individual may have choked to death on these ribs. [6] However, Smith et al. concluded that these remains belonged to the Cryolophosaurus specimen itself, and not to Hammer's "prosauropod". [18] Hammer also concluded that a post-canine tooth belonging to a tritylodont (an early mammal relative), found with the remains, was part of its stomach contents when it died. [30]

Paleopathology

Cryolophosaurus left tibia (upper) and left tibia and fibula (lower) with calcaneum and astragalus Cryolophosaurus Left Tibia Fossil.jpg
Cryolophosaurus left tibia (upper) and left tibia and fibula (lower) with calcaneum and astragalus

Some Cryolophosaurus bones have pathologies that show evidence of scavenging. Broken teeth from a juvenile Cryolophosaurus were found nearby. [28] These teeth have no roots and likely shed naturally while scavenging the adult Cryolophosaurus carcass.

Another possible pathology is found in the astragalus (ankle bone) of Cryolophosaurus. This bone was preserved with a small splint from the fibula located just above the ankle. The splint, however, may also be just a unique morphological feature of Cryolophosaurus. [7]

Paleoenvironment

Some sediments in the Hanson Formation are of volcanic origin, suggesting Plinian eruptions during the deposition Fire storm.jpg
Some sediments in the Hanson Formation are of volcanic origin, suggesting Plinian eruptions during the deposition

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. Cryolophosaurus was found about 650 kilometres (400 mi) from the South Pole but, [6] at the time it lived, this was about 1,000 km (621 mi) or so farther north. [31] The Hanson Formation accumulated in a rift environment located between c. 60 and 70S, fringing the East Antarctic Craton behind the active Panthalassan margin of southern Gondwana, being dominated by two types of facies: "tuffaceous" siltstone of fluvial and volcanic strata, deposited maybe more than 10 million years based on the thickness. [32] 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 similar to that of modern southern Chile, and humid, with a temperature interval of 17–18 degrees. Models of Jurassic air flow indicate that coastal areas probably never dropped much below freezing, although more extreme conditions existed inland. [33]

This formation has produced the remains of two smaller theropods, the sauropodomorph Glacialisaurus , [34] a crow-sized pterosaur (a dimorphodontid), a tritylodont, herbivorous synapsid, and two small unnamed sauropodomorphs. [35] [36] Beyond vertebrates, Insects (Blattodea, Coleoptera), Ostracodans, Conchostracans and arthropod ichnofossils ( Diplichnites, Planolites, Scoyenia ) are know from other coeval localities, like Gair Mesa, Mount Carson or Shafer Peak. [37] Plant remains are also very common, from large tree trunks (+50 cm) at Mount Carson to Palynomorphs at Shafer Peak. [38] Macrofoliar and cuticle remains have also been recovered from seveal localities, including Conifers (Araucariaceae, Cheirolepidiaceae, Cupressaceae, Pinaceae or Voltziales), Cycadophytes (Bennettitales), Pteridosperms (Corystospermaceae), Ferns (Dipteridaceae, Matoniaceae, Osmundaceae and Polypodiales), Equisetaceae, Isoetaceae and Liverworts (Marchantiales). [39] Some of the plant remains are relictual genera, like the youngest record of Dicroidium. [40] Common presence of the invertebrate ichnogenus Planolites indicates the local fluvial, alluvial or lacustrine waters where likely continuous all year, as well the presence of abundant Otozamites trends to suggest high humidity. [39] Overall points to a setting with strong seasonality in day-length given the high latitude, perhaps similar to warm-temperate, frost-free forest and open woodland as in North Island of New Zealand. Despite the proper conditions, peat accumulation was rare, mostly due to the influence of local volcanism, with common wildfire activity as shown by charred coalified plant remains. [39]

Related Research Articles

<i>Dilophosaurus</i> Genus of theropod dinosaur from Early Jurassic

Dilophosaurus is a genus of theropod dinosaurs that lived in what is now North America during the Early Jurassic, about 186 million years ago. Three skeletons were discovered in northern Arizona in 1940, and the two best preserved were collected in 1942. The most complete specimen became the holotype of a new species in the genus Megalosaurus, named M. wetherilli by Samuel P. Welles in 1954. Welles found a larger skeleton belonging to the same species in 1964. Realizing it bore crests on its skull, he assigned the species to the new genus Dilophosaurus in 1970, as Dilophosaurus wetherilli. The genus name means "two-crested lizard", and the species name honors John Wetherill, a Navajo councilor. Further specimens have since been found, including an infant. Fossil footprints have also been attributed to the animal, including resting traces. Another species, Dilophosaurus sinensis from China, was named in 1993, but was later found to belong to the genus Sinosaurus.

<span class="mw-page-title-main">Tetanurae</span> Clade containing most theropod dinosaurs

Tetanurae is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans. Tetanurans are defined as all theropods more closely related to modern birds than to Ceratosaurus and contain the majority of predatory dinosaur diversity. Tetanurae likely diverged from its sister group, Ceratosauria, during the late Triassic. Tetanurae first appeared in the fossil record by the Early Jurassic about 190 mya and by the Middle Jurassic had become globally distributed.

<span class="mw-page-title-main">Coelophysoidea</span> Extinct superfamily of dinosaurs

Coelophysoidea were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the coelurosaurs, with which they were formerly classified, and some species had delicate cranial crests. Sizes range from about 1 to 6 m in length. It is unknown what kind of external covering coelophysoids had, and various artists have portrayed them as either scaly or feathered. Some species may have lived in packs, as inferred from sites where numerous individuals have been found together.

<span class="mw-page-title-main">Allosauridae</span> Extinct family of theropod dinosaurs

Allosauridae is a family of medium to large bipedal, carnivorous allosauroid theropod dinosaurs from the Late Jurassic. Allosauridae is a fairly old taxonomic group, having been first named by the American paleontologist Othniel Charles Marsh in 1878. Allosaurids are characterized by an astragalus with a restriction of the ascending process to the lateral part of the bone, a larger medial than lateral condyle, and a horizontal groove across the face of the condyles.

<i>Monolophosaurus</i> Extinct genus of dinosaurs

Monolophosaurus is an extinct genus of tetanuran theropod dinosaur from the Middle Jurassic Shishugou Formation in what is now Xinjiang, China. It was named for the single crest on top of its skull. Monolophosaurus was a mid-sized theropod at about 5–5.5 metres (16–18 ft) long and weighed 475 kilograms (1,047 lb).

<i>Piatnitzkysaurus</i> Extinct genus of dinosaurs

Piatnitzkysaurus is a genus of megalosauroid theropod dinosaur that lived approximately 179 to 177 million years ago during the lower part of the Jurassic Period in what is now Argentina. Piatnitzkysaurus was a moderately large, lightly built, bipedal, ground-dwelling carnivore that could grow up to 6.6 m (21.7 ft) long.

<i>Sinosaurus</i> Genus of dinosaurs

Sinosaurus is an extinct genus of theropod dinosaur which lived during the Early Jurassic Period. It was a bipedal carnivore approximately 5.5 metres (18 ft) in length and 300 kilograms (660 lb) in body mass. Fossils of the animal were found at the Lufeng Formation, in the Yunnan Province of China.

<i>Zupaysaurus</i> Extinct genus of dinosaurs

Zupaysaurus is an extinct genus of early theropod dinosaur living during the Norian stage of the Late Triassic in what is now Argentina. Fossils of the dinosaur were found in the Los Colorados Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina. Although a full skeleton has not yet been discovered, Zupaysaurus can be considered a bipedal predator, up to 4 metres (13 ft) long. It may have had two parallel crests running the length of its snout.

<span class="mw-page-title-main">Allosauroidea</span> Extinct superfamily of Dinosaurs

Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Metriacanthosauridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae. Allosauroids, alongside the family Megalosauroidea, were among the apex predators that were active during the Middle Jurassic to Late Cretaceous periods. The most famous and best understood allosauroid is the North American genus Allosaurus.

<i>Dracovenator</i> Extinct genus of dinosaur from the Jurassic of South Africa

Dracovenator is a genus of neotheropod dinosaur that lived approximately 201 to 199 million years ago during the early part of the Jurassic Period in what is now South Africa. Dracovenator was a medium-sized, moderately-built, ground-dwelling, bipedal carnivore, that could grow up to an estimated 5.5–6.5 metres (18–21 ft) in length and 250 kilograms (550 lb) in body mass. Its type specimen was based on only a partial skull that was recovered.

<span class="mw-page-title-main">Hanson Formation</span> Geological formation in Ross Dependency, Antarctica

The Hanson Formation is a geologic formation on Mount Kirkpatrick and north Victoria Land, Antarctica. It is one of the two major dinosaur-bearing rock groups found on Antarctica to date; the other is the Snow Hill Island Formation and related formations from the Late Cretaceous of the Antarctic Peninsula. The formation has yielded some Mesozoic specimens, but most of it is as yet unexcavated. Part of the Victoria Group of the Transantarctic Mountains, it lies below the Prebble Formation and above the Falla Formation. The formation includes material from volcanic activity linked to the Karoo-Ferar eruptions of the Lower Jurassic. The climate of the zone was similar to that of modern southern Chile, humid, with a temperature interval of 17–18 degrees. The Hanson Formation is correlated with the Section Peak Formation of the Eisenhower Range and Deep Freeze Range, as well as volcanic deposits on the Convoy Range and Ricker Hills of southern Victoria Land. Recent work has successfully correlated the Upper Section Peak Formation, as well unnamed deposits in Convoy Range and Ricker Hills with the Lower Hanson, all likely of Sinemurian age and connected by layers of silicic ash, while the upper section has been found to be Pliensbachian, and correlated with a greater volcanic pulse, marked by massive ash inputs.

<i>Glacialisaurus</i> Extinct genus of dinosaurs

Glacialisaurus is a genus of sauropodomorph dinosaur. It lived during the Pliensbachian stage of the Early Jurassic period around 186 to 182 million years ago in what is now the central region of the Transantarctic Mountains of Antarctica. It is known from two specimens; the holotype, a partial tarsus (ankle) and metatarsus, and a partial left femur. The fossils were collected by a team led by paleontologist William R. Hammer during a 1990–91 field expedition to the Hanson Formation of Antarctica. They were described in 2007, and made the basis of the new genus and species Glacialisaurus hammeri. The genus name translates as “icy” or "frozen lizard”, and the species name honors Hammer.

William Roy Hammer is an American paleontologist who is credited with the discovery of the first carnivorous dinosaur unearthed in Antarctica, Cryolophosaurus, in 1991. He was professor of geology and curator of the Frxyell Geology Museum at Augustana College in Rock Island, IL from 1981 to 2017.

<span class="mw-page-title-main">Neotheropoda</span> Clade of theropods

Neotheropoda is a clade that includes coelophysoids and more advanced theropod dinosaurs, and is the only group of theropods that survived the Triassic–Jurassic extinction event. All neotheropods became extinct by the end of the Early Jurassic except for Averostra.

Kayentavenator is a genus of small carnivorous tetanuran dinosaur that lived during the Early Jurassic Period; fossils were recovered from the Kayenta Formation of northeastern Arizona and were described in 2010.

<i>Sarahsaurus</i> Extinct genus of dinosaurs

Sarahsaurus is a genus of basal sauropodomorph dinosaur which lived during the Early Jurassic period in what is now northeastern Arizona, United States.

<span class="mw-page-title-main">Averostra</span> Clade of dinosaurs

Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs, namely Ceratosauria and Tetanurae, and represent the only group of post-Early Jurassic theropods. Both survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians, megaraptorans an incertae sedis group within Tetanurae, and two groups of tetanurans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of Maniraptoriformes, Aves, survived the extinction event and persisted to the present day.

<i>Megapnosaurus</i> Extinct genus of dinosaur

Megapnosaurus is an extinct genus of coelophysid theropod dinosaur that lived approximately 188 million years ago during the early part of the Jurassic Period in what is now Africa. The species was a small to medium-sized, lightly built, ground-dwelling, bipedal carnivore, that could grow up to 2.2 m (7.2 ft) long and weigh up to 13 kg (29 lb). It was originally given the genus name Syntarsus, but that name was later determined to be preoccupied by a beetle. The species was subsequently given a new genus name, Megapnosaurus, by Ivie, Ślipiński & Węgrzynowicz in 2001. Some studies have classified it as a species within the genus Coelophysis, but this interpretation has been challenged by more subsequent studies and the genus Megapnosaurus is now considered valid.

<i>Coelophysis</i>? <i>kayentakatae</i> Extinct species of dinosaur

Coelophysis? kayentakatae is an extinct species of neotheropod dinosaur that lived approximately 200–196 million years ago during the early part of the Jurassic Period in what is now the southwestern United States. It was originally named Syntarsus kayentakatae, but the genus Syntarsus was found to be preoccupied by a Colydiine beetle, so it was moved to the genus Megapnosaurus, and then to Coelophysis. A recent reassessment suggests that this species may require a new genus name.

Shuangbaisaurus is genus of theropod dinosaur, possibly a junior synonym of Sinosaurus. It lived in the Early Jurassic of Yunnan Province, China, and is represented by a single species, S. anlongbaoensis, known from a partial skull. Like the theropods Dilophosaurus and Sinosaurus,Shuangbaisaurus bore a pair of thin, midline crests on its skull. Unusually, these crests extended backwards over the level of the eyes, which, along with the unusual orientation of the jugal bone, led the describers to name it as a new genus. However, Shuangbaisaurus also possesses a groove between its premaxilla and maxilla, a characteristic which has been used to characterize Sinosaurus as a genus. Among the two morphotypes present within the genus Sinosaurus, Shuangbaisaurus more closely resembles the morphotype that is variably treated as a distinct species, S. sinensis, in its relatively tall skull.

References

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  3. ↑ Pickrell, John (2004). "Two New Dinosaurs Discovered in Antarctica". National Geographic. Archived from the original on March 11, 2004. Retrieved 20 December 2013.
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  5. ↑ Leslie, M (2007). "The Strange Lives of Polar Dinosaurs". Smithsonian Magazine. Archived from the original on 2012-07-02. Retrieved 2008-01-24.
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  7. 1 2 3 4 Smith, N.D.; Makovicky, P.J.; Hammer, W.R.; Currie, P.J. (2007). "Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica and implications for early theropod evolution" (PDF). Zoological Journal of the Linnean Society. 151 (2): 377–421. doi: 10.1111/j.1096-3642.2007.00325.x .[ permanent dead link ]
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