Cryolophosaurus

''Cryolophosaurus'' ( or ; ) 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 long and weighed .

''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. ''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

''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 back 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.

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 high and about from the South Pole. When the discovery was made, they soon notified Hammer. Over the next three weeks, Hammer excavated 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 Hickerson, in the journal ''Science''.

During the 2003 season, a field team returned and collected more material from the original site. A second locality was discovered about higher in the section on Mt. Kirkpatrick.

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 (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.

Description

''Cryolophosaurus'' was a large, well-built theropod, one of the largest of its time. The holotype specimen is estimated to have reached long and weighed . In 2016 Molina-Pérez and Larramendi gave a larger estimation of 7.7 meters (25.3 ft) and 780 kg (1,720 lb). Some researchers noted that the holotype individual probably represents a sub-adult, so adults could have been larger. Despite having slender proportions, ''Cryolophosaurus'' is one of the largest known Early Jurassic theropods.

The holotype FMNH PR1821 is the only fully described specimen of ''Cryolophosaurus''. The specimen consists of an incomplete skull and mandibles, lacking most of the 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. 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.

Skull

The holotype of ''C. ellioti'' consists of a high, narrow skull, which was discovered articulated with the rest of the skeleton. The skull is an estimated 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 " Elvisaurus." 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.

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. Closer examination of how the skull bones fused reviewed details in the snout and forehead that are exceptionally similar to '' Dilophosaurus''.

Classification

Classification of ''Cryolophosaurus'' is difficult because it 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 Paul Sereno ''et al.'' (1994) to place ''Cryolophosaurus'' in the taxon Allosauridae. Originally, Hammer and colleagues suspected that ''C. ellioti'' 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''. 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. However, in 2012, Matthew Carrano found that ''Cryolophosaurus'' was a tetanuran, related to '' Sinosaurus'', but unrelated to ''Dilophosaurus''. 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''.

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

However, a 2020 study conducted by Adam Marsh and Timothy Rowe found ''C. ellioti'' to be a basal Neotheropod. While it was still closer to ''Averostra'' than ''Co''e''physoidea'' was, it was still more basal than ''Dilophosaurus''.

Paleobiology

Cranial ornamentation

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. 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. Thomas R. Holtz Jr. (2010) found that the bizarre crest of ''C. llioti'' was primarily for intra-species recognition, based on evidence from related species and studies of bone texture. 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. In 2019, a species recognition function was disputed but a socio-sexual display structure model was suggested.

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. However, Smith ''et al.'' concluded that these remains belonged to the ''Cryolophosaurus'' specimen itself, and not to Hammer's "prosauropod". 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.

Paleopathology

Some ''Cryolophosaurus'' bones have pathologies that show evidence of scavenging. Broken teeth from a juvenile ''Cryolophosaurus'' were found nearby. 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''.

Paleoenvironment

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 from the South Pole but, at the time it lived, this was about or so farther north. 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. 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.

This formation has produced the remains of two smaller theropods, the sauropodomorph ''Glacialisaurus'', a crow-sized pterosaur (a dimorphodontid), a tritylodont, herbivorous synapsid, and two small unnamed sauropodomorphs. 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. Plant remains are also very common, including large tree trunks (+50 cm) from Mount Carson to Palynomorphs at Shafer Peak. Macrofoliar and cuticle remains have also been recovered from several localities, including Conifers (Araucariaceae, Cheirolepidiaceae, Cupressaceae, Pinaceae or Voltziales), Cycadophytes ( Bennettitales), Pteridosperms ( Corystospermaceae), Ferns ( Dipteridaceae, Matoniaceae, Osmundaceae and Polypodiales), Equisetaceae, Isoetaceae and Liverworts ( Marchantiales). Some of the plant remains are relictual genera, like the youngest record of Dicroidium. 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. 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, alongside with common wildfire activity as shown by charred coalified plant remains.

References

External links

Transantarctic Vertebrate Paleontology Project
official website for the NSF project conducting research on Cryolophosaurus and related fauna (photos, research information, publication list, geology, project members ...)


(photos, information)

Field Museum of Natural History
(video, information)

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Theropoda
Dinosaur genera
Pliensbachian dinosaurs
Dinosaurs of Antarctica
Fossil taxa described in 1994
Taxa named by William R. Hammer