Ceratosaurus, meaning "horned lizard", is a genus of ceratosaurid theropod dinosaur from the Kimmeridgian and Tithonian stages of the Late Jurassic period of North America, Africa, and Europe. It is characterized by large jaws with blade-like teeth, a large, blade-like horn on the snout and a pair hornlets over the eyes. Ceratosaurus has three little horns on its head, near its snout. The top teeth of this pretador were very long compared to top teeth of other theropod. It could grow about 6 feet (1.8 metres) tall and 22 feet (6.7 metres) long. It was a mid-sized theropod that was discovered in 1884 and was considered a Megalosaurus species for a while, similar to numerous other theropods that were described at the time. In popular culture, it has been one of the most well-known theropods, especially during most of the 20th century.
Description[]
Ceratosaurus followed the body plan typical of large theropod dinosaurs. It was bipedal and moved on powerful hindlimbs, while its arms were reduced in size. Ceratosaurus is characterized by having a horn-like structure on the dorsal side of the head, placed behind the nostrils. Ceratosaurus had a fused sacrum and synsacrum, while the pelvic bones were fused together. Unique among most theropods, Ceratosaurus had dermal armor, with small osteoderms that ran down the middle of its back. Its tail was about half its total body length, and was thin and flexible, with tall vertebral spines that occurred in the middle of its back. Ceratosaurus had three teeth on its premaxilla with small mesial serrations. On the pubis Ceratosaurus had a large, rounded notch below the obturator foramen.
Size[]
Size of two specimens compared to a human, with the holotype of Ceratosaurus nasicornis (USNM 4735) in orange and a larger specimen (UMNH VP 5278) in blue
The holotype specimen of Ceratosaurus corresponds to an individual of about 5.3 meters long and 2 meters tall, it is not clear if this Ceratosaurus had fully developed. David B. Norman in 1985 estimated that the maximum length of Ceratosaurus was 6.1 meters long, although an evaluation made on specimen UMNH 5728 could be established that this was particularly large, being able to measure up to 6.7 meters long assuming proportions similar to those of the holotype, and could have weighed approximately between 418.4 and 670 kilograms.
Marsh in 1884 suggested that Ceratosaurus was half the weight of Allosaurus , which he estimated to have weighed 2 tonnes. Gregory S. Paul in Predatory Dinosaurs of the World , published in 1988, estimates that the holotype specimen of C. nasicornis came from an animal weighing approximately 524 kilograms (1,100 lb), while other material from the Cleveland-Lloyd Quarry was from a much larger and heavier individual, weighing around 980 kilograms (2,000 lb).
Two skeletons, assigned to the new species C. magnicornis and C. dentisulcatus by James H. Madsen and Samuel P. Welles in a 2000 paper, were much larger than the holotype. The largest of these, C. dentisuclatus, was informally estimated by Madsen to be about 8.8 metres (28 ft) long. Gregory S. Paul, in 1988, estimated the C. dentisulcatus specimen at 980 kilograms (2,000 lb). A considerably lower figure, 275 kilograms (600 lb) for C. magnicornis and 452 kilograms (989 lb) for C. dentisulcatus, was proposed by John Foster in 2007.
Skull[]
Diagram of the Ceratosaurus nasicornis holotype skull in top and side view by Charles Gilmore, 1920: This reconstruction is now thought to be too wide in top view.
Ceratosaurus at first glance appeared to be a fairly typical theropod, however its skull was quite large in proportion to the rest of its body and it possessed a very large nasal horn, formed from the protuberances of the nasal bones. In addition to the large nasal horn, Ceratosaurus possessed small, horn-like crests in front of each eye, similar to the crests of Allosaurus, which were formed by the upward enlargement of the lacrimal bones.
The skull was fairly large in proportion to the rest of the body, measuring 62.5 centimetres (24.8 in) in length in the holotype. Its most distinctive feature was a prominent horn, which was situated on the midline of the skull behind the nostrils. Only the bony horn core is known from fossils; in the living animal, this core would have supported a keratinous sheath. In the holotype, the horn core measures 13 centimetres (5.1 in) long and 2 centimetres (0.8 in) wide at its base, but rapidly tapers to just 1.2 centimetres (0.4 in) higher up; it is 7 centimetres (2.7 in) tall. The horn core was formed from co-ossified protuberances of the paired left and right nasal bones. In juveniles, the halves of the horn core were not yet co-ossified. In addition to the large nasal horn, Ceratosaurus possessed smaller horn crests in front of each eye, similar to those of Allosaurus, these crests being formed by the lacrimal bones. All three horns were larger in adults than in juveniles.
Cast of the skull of the C. nasicornis holotype, showing the large nasal horn, American Museum of Natural History
The upper jaws were lined with 12 to 15 blade-like teeth on each side. The premaxilla, which formed the tip of the snout, contained only three teeth on each half, fewer than in most other theropods. Each half of the lower jaw was equipped with 11 to 15 teeth that were slightly straighter and less robust than those of the upper jaw. The tooth crowns of the upper jaw were exceptionally long, measuring up to 9.3 centimetres (3.7 in) in length in the largest specimen, which is equal to the minimum height of the lower jaw. In the smallest holotype specimen, the length of the upper tooth crowns (7 centimetres) even exceeds the minimum lower jaw height of 6.3 centimetres (2.5 in). In other theropods, this feature is only known from the possibly closely related Geniodectes. In contrast, several related members of the Abelisauridae have very low tooth crowns.
Arms[]
The arms of Ceratosaurus were relatively short, as in other basal representatives of Ceratosauria. Ceratosaurus had four fingers on its hand, a very ancient feature in theropods. Several specimens are known, including the fragmentary arm of specimen AMNH 27631 in the American Museum of Natural History (see image), from which the exact number of phalanges can be determined. It can also be seen that the first and fourth metacarpals are very short, while the second metacarpal was slightly longer than the third.
Axial Skeleton[]
Artist's impression of C. nasicornis
Distinguishing skull features of Ceratosaurus: The fused left and right nasal bones form a prominent nasal horn (top), and the teeth of the upper jaw are exceptionally long (bottom). These fossils are part of specimen MWC 1 from Fruita, Colorado, and are on display at the local Dinosaur Journey Museum.
The exact number of vertebrae is unknown due to several gaps in the holotype spine. The sacrum consisted of 6 fused sacral vertebrae. At least 20 presacral vertebrae formed the vertebral column of the neck, back, and abdomen. 50 vertebrae make up the tail. The latter comprised about half the total body length. As in other dinosaurs, it counterbalanced the body and contained the massive caudofemoral muscle, which was responsible for forward momentum during locomotion, pulling the upper torsion backward when it contracted. The tail of Ceratosaurus was characterized by comparatively tall neural spines, upward-directed bony processes on the caudal vertebrae, and by elongated chevrons, bones located beneath the tail vertebrae, giving the tail a deep profile in side view. Unlike most other theropods, Ceratosaurus possessed a row of small, elongated, irregularly shaped osteoderms running down the middle of its neck, back, and most of its tail. In addition to the midline of the body, the skin contained additional osteoderms, as indicated by a large 6 × 7 centimeter plate found with the holotype specimen; the position of this plate on the body is unknown.
History of discovery[]
Holotype specimen of C. nasicornis[]
C. nasicornis skeleton restoration by Othniel Charles Marsh from 1896, depicted in an erroneous upright position and with excess vertebrae in the spine resulting in an overly elongated trunk
The first specimen, the holotype USNM 4735, was discovered and excavated by farmer Marshall Parker Felch in 1883 and 1884. Found in articulation, with the bones still connected to each other, it was nearly complete, including the skull. Significant missing parts include an unknown number of vertebrae; all but the last ribs of the trunk; the humeri (upper arm bones); the distal finger bones of both hands; most of the right fore limb; most of the left hind limb; and most of the feet. The specimen was found encased in hard sandstone; the skull and spine had been heavily distorted during fossilization. The site of discovery, located in the Garden Park area north of Cañon City, Colorado, and known as the Felch Quarry 1, is regarded as one of the richest fossil sites of the Morrison Formation. Numerous dinosaur fossils had been recovered from this quarry even before the discovery of Ceratosaurus, most notably a nearly complete specimen of Allosaurus (USNM 4734) in 1883 and 1884.
After excavation, the specimen was shipped to the Peabody Museum of Natural History in New Haven, where it was studied by Marsh, who described it as the new genus and species Ceratosaurus nasicornis in 1884. The name Ceratosaurus may be translated as "horn lizard" (from Greek κερας/κερατος, keras/keratos—"horn" and σαυρος/sauros—"lizard"), and nasicornis with "nose horn" (from Latin nasus—"nose" and cornu—"horn"). Given the completeness of the specimen, the newly described genus was at the time the best-known theropod discovered in America. In 1898 and 1899, the specimen was transferred to the National Museum of Natural History in Washington, DC, together with many other fossils originally described by Marsh. Only part of this material was fully prepared when it arrived in Washington; subsequent preparation lasted from 1911 to the end of 1918. Packaging and shipment from New Haven to Washington caused some damage to the Ceratosaurus specimen. In 1920, Charles Gilmore published an extensive redescription of this and the other theropod specimens received from New Haven, including the nearly complete Allosaurus specimen recovered from the same quarry.
Reconstruction of the holotype specimen of C. nasicornis by Charles W. Gilmore, 1920, showing known elements
In an 1892 paper, Marsh published the first skeletal reconstruction of Ceratosaurus, which depicts the animal at 22 ft (6.7 m) in length and 12 ft (3.7 m) in height. As noted by Gilmore in 1920, the trunk was depicted much too long in this reconstruction, incorporating at least six dorsal vertebrae too many. This error was repeated in several subsequent publications, including the first life reconstruction, which was drawn in 1899 by Frank Bond under the guidance of Charles R. Knight, but not published until 1920. A more accurate life reconstruction, published in 1901, was produced by Joseph M. Gleeson, again under Knight's supervision. The holotype was mounted by Gilmore in 1910 and 1911, and since then was exhibited at the National Museum of Natural History. Most early reconstructions show Ceratosaurus in an upright posture, with the tail dragging on the ground. Gilmore's mount of the holotype, in contrast, was ahead of its time: Inspired by the upper thigh bones, which were found angled against the lower leg, he depicted the mount as a running animal with a horizontal rather than upright posture and a tail that did not make contact with the ground. Because of the strong flattening of the fossils, Gilmore mounted the specimen not as a free-standing skeleton, but as a bas-relief within an artificial wall. With the bones being partly embedded in a plaque, scientific access was limited. In the course of the renovation of the museum's dinosaur exhibition between 2014 and 2019, the specimen was dismantled and freed from the encasing plaque. In the new exhibition, which is set to open in 2019, the mount is planned to be replaced by a free-standing cast, and the original bones to be stored in the museum collection to allow full access for scientists.
Probably the first life restoration of Ceratosaurus, drawn in 1899 by Frank Bond under the guidance of Charles R. Knight, but not published until 1920
Additional finds in North America[]
After the discovery of the holotype of C. nasicornis, a significant Ceratosaurus find was not made until the early 1960s, when paleontologist James Madsen and his team unearthed a fragmentary, disarticulated skeleton including the skull (UMNH VP 5278) in the Cleveland-Lloyd Dinosaur Quarry in Utah. This find represents one of the largest-known Ceratosaurus specimens. A second, articulated specimen including the skull (MWC 1) was discovered in 1976 by Thor Erikson, the son of paleontologist Lance Erikson, near Fruita, Colorado. A fairly complete specimen, it lacks lower jaws, forearms and gastralia. The skull, although reasonably complete, was found disarticulated and is strongly flattened sidewards. Although a large individual, it had not yet reached adult size, as indicated by open sutures between the skull bones. Scientifically accurate three-dimensional reconstructions of the skull for use in museum exhibits were produced using a complicated process including molding and casting of the individual original bones, correction of deformities, reconstruction of missing parts, assembly of the bone casts into their proper position, and painting to match the original color of the bones.
Both the Fruita and Cleveland-Lloyd specimens were described by Madsen and Samuel Paul Welles in a 2000 monograph, with the Utah specimen being assigned to the new species C. dentisulcatus and the Colorado specimen to the new species C. magnicornis. The name dentisulcatus refers to the parallel grooves present on the inner sides of the premaxillary teeth and the first three teeth of the lower jaw in that specimen; magnicornis points to the larger nasal horn. The validity of both species, however, was questioned in subsequent publications. Brooks Britt and colleagues, in 2000, claimed that the C. nasicornis holotype was in fact a juvenile individual, with the two larger species representing the adult state of a single species. Oliver Rauhut, in 2003, and Matthew Carrano and Scott Sampson, in 2008, considered the anatomical differences cited by Madsen and Welles to support these additional species to represent ontogenetic (age-related) or individual variation. A further specimen (BYUVP 12893) was discovered in 1992 in the Agate Basin Quarry southeast of Moore, Utah, but still awaits description. The specimen, considered the largest known from the genus, includes the front half of a skull, seven fragmentary pelvic dorsal vertebrae, and an articulated pelvis and sacrum. In 1999, Britt reported the discovery of a Ceratosaurus skeleton belonging to a juvenile individual. Discovered in Bone Cabin Quarry in Wyoming, it is 34% smaller than the C. nasicornis holotype and consists of a complete skull as well as 30% of the remainder of the skeleton including a complete pelvis.
Besides these five skeletal finds, fragmentary Ceratosaurus remains have been reported from various localities from stratigraphic zones 2 and 4-6 of the Morrison Formation, including some of the major fossil sites of the formation. Dinosaur National Monument, Utah, yielded an isolated right premaxilla (specimen number DNM 972); a large shoulder blade (scapulocoracoid) was reported from Como Bluff in Wyoming. Another specimen stems from the Dry Mesa Quarry, Colorado, and includes a left scapulocoracoid, as well as fragments of vertebrae and limb bones. In Mygatt Moore Quarry, Colorado, the genus is known from teeth.
Finds outside North America[]
From 1909 to 1913, German expeditions of the Berlin Museum für Naturkunde uncovered a diverse dinosaur fauna from the Tendaguru Formation in German East Africa, in what is now Tanzania. Although commonly considered the most important African dinosaur locality, large theropod dinosaurs are only known through few and very fragmentary remains. In 1920, German paleontologist Werner Janensch assigned several dorsal vertebrae from the quarry "TL" to Ceratosaurus, as Ceratosaurus sp. (of uncertain species). In 1925, Janensch named a new species of Ceratosaurus, C. roechlingi, based on fragmentary remains from the quarry "Mw" encompassing a quadrate bone, a fibula, fragmentary caudal vertebrae, and other fragments. This specimen stems from an individual substantially larger than the C. nasicornis holotype.
Restoration of C. nasicornis by Joseph M. Gleeson from 1901, made under supervision of Charles R. Knight.
In their 2000 monograph, Madsen and Welles confirmed the assignment of these finds to Ceratosaurus. In addition, they ascribed several teeth to the genus, which had originally been described by Janensch as a possible species of Labrosaurus, Labrosaurus (?) stechowi. Other authors questioned the assignment of any of the Tendaguru finds to Ceratosaurus, noting that none of these specimens displays features diagnostic for that genus. In 2011, Rauhut found both C. roechlingi and Labrosaurus (?) stechowi to be possible ceratosaurids, but found them to be not diagnostic at genus level and therefore designated them as nomina dubia (doubtful names). In 1990, Timothy Rowe and Jacques Gauthier mentioned yet another Ceratosaurus species from Tendaguru, Ceratosaurus ingens, which purportedly was erected by Janensch in 1920 and was based on 25 isolated, very large teeth up to 15 cm (5.9 in) in length. However, Janensch assigned this species to Megalosaurus, not to Ceratosaurus; therefore, this name might be a simple copying error. Rauhut, in 2011, showed that Megalosaurus ingens was not closely related to either Megalosaurus or Ceratosaurus, but possibly represents a carcharodontosaurid, instead.
In 2000 and 2006, paleontologists led by Octávio Mateus described a find from the Lourinhã Formation in central-west Portugal (ML 352) as a new specimen of Ceratosaurus, consisting of a right femur (upper thigh bone), a left tibia (shin bone), and several isolated teeth recovered from the cliffs of Valmitão beach, between the municipalities Lourinhã and Torres Vedras. The bones were found embedded in yellow to brown, fine-grained sandstones, which were deposited by rivers as floodplain deposits and belong to the lower levels of the Porto Novo Member, which is thought to be late Kimmeridgian in age. Additional bones of this individual (SHN (JJS)-65), including a left femur, a right tibia, and a partial left fibula (calf bone), were since exposed due to progressing cliff erosion. Although initially part of a private collection, these additional elements became officially curated after the private collection was donated to the Sociedade de História Natural in Torres Vedras, and were described in detail in 2015. The specimen was ascribed to the species Ceratosaurus dentisulcatus by Mateus and colleagues in 2006. A 2008 review by Carrano and Sampson confirmed the assignment to Ceratosaurus, but concluded that the assignment to any specific species is not possible at present. In 2015, Elisabete Malafaia and colleagues, who questioned the validity of C. dentisulcatus, assigned the specimen to Ceratosaurus aff. Ceratosaurus nasicornis.
Other reports include a single tooth found in Moutier, Switzerland. Originally named by Janensch in 1920 as Labrosaurus meriani, the tooth was later assigned Ceratosaurus sp. (of unknown species) by Madsen and Welles. In 2008, Matías Soto and Daniel Perea described teeth from the Tacuarembó Formation in Uruguay, including a presumed premaxillary tooth crown. This shows vertical striations on its inner side and lacks denticles on its front edge; these features are, in this combination, only known from Ceratosaurus. The authors, however, stressed that an assignment to Ceratosaurus is infeasible as the remains are scant, and furthermore note that the assignment of the European and African material to Ceratosaurus has to be viewed with caution. In 2020, Soto and colleagues described additional Ceratosaurus teeth from the same formation that further support their earlier interpretation.
Classification[]
C. nasicornis holotype, as mounted by Charles Gilmore in 1910 and 1911, National Museum of Natural History
In his original description of the Ceratosaurus nasicornis holotype and subsequent publications, Marsh noted a number of characteristics that were unknown in all other theropods known at the time. Two of these features, the fused pelvis and fused metatarsus, were known from modern-day birds, and according to Marsh, clearly demonstrate the close relationship between the latter and dinosaurs. To set the genus apart from Allosaurus, Megalosaurus, and coelurosaurs, Marsh made Ceratosaurus the only member of both a new family, the Ceratosauridae, and a new infraorder, the Ceratosauria. This was questioned in 1892 by Edward Drinker Cope, Marsh's rival in the Bone Wars, who argued that distinctive features such as the nasal horn merely showed that C. nasicornis was a distinct species, but were insufficient to justify a distinct genus. Consequently, he assigned C. nasicornis to the genus Megalosaurus, creating the new combination Megalosaurus nasicornis.
Although Ceratosaurus was retained as a distinct genus in all subsequent analyses, its relationships remained controversial during the following century. Both the Ceratosauridae and Ceratosauria were not widely accepted, with only few and poorly known additional members identified. Over the years, separate authors classified Ceratosaurus within the Deinodontidae, the Megalosauridae, the Coelurosauria, the Carnosauria, and the Deinodontoidea. In his 1920 revision, Gilmore argued that the genus was the most basal theropod known from after the Triassic, so not closely related to any other contemporary theropod known at that time; it thus warrants its own family, the Ceratosauridae. It was not until the establishment of cladistic analysis in the 1980s, however, that Marsh's original claim of the Ceratosauria as a distinct group gained ground. In 1985, the newly discovered South American genera Abelisaurus and Carnotaurus were found to be closely related to Ceratosaurus. Gauthier, in 1986, recognized the Coelophysoidea to be closely related to Ceratosaurus, although this clade falls outside of Ceratosauria in most recent analyses. Many additional members of the Ceratosauria have been recognized since.
The Ceratosauria split off early from the evolutionary line leading to modern birds, thus is considered basal within theropods. Ceratosauria itself contains a group of derived (nonbasal) members of the families Noasauridae and Abelisauridae, which are bracketed within the clade Abelisauroidea, as well as a number of basal members, such as Elaphrosaurus, Deltadromeus, and Ceratosaurus. The position of Ceratosaurus within basal ceratosaurians is under debate. Some analyses considered Ceratosaurus as the most derived of the basal members, forming the sister taxon of the Abelisauroidea. Oliver Rauhut, in 2004, proposed Genyodectes as the sister taxon of Ceratosaurus, as both genera are characterized by exceptionally long teeth in the upper jaw. Rauhut grouped Ceratosaurus and Genyodectes within the family Ceratosauridae, which was followed by several later accounts.
Shuo Wang and colleagues, in 2017, concluded that the Noasauridae were not nested within the Abelisauroidea as was previously assumed, but instead were more basal than Ceratosaurus. Because noasaurids had been used as a fix point to define the clades Abelisauroidea and Abelisauridae, these clades would consequently include many more taxa per definition, including Ceratosaurus. In a subsequent 2018 study, Rafael Delcourt accepted these results, but pointed out that, as a consequence, the Abelisauroidea would need to be replaced by the older synonym Ceratosauroidea, which was hitherto rarely used. For the Abelisauridae, Delcourt proposed a new definition that excludes Ceratosaurus, allowing for using the name its traditional sense. Wang and colleagues furthermore found that Ceratosaurus and Genyodectes form a clade with the Argentinian genus Eoabelisaurus. Delcourt used the name Ceratosauridae to refer to this same clade, and suggested to define the Ceratosauridae as containing all taxa that are more closely related to Ceratosaurus than to the abelisaurid Carnotaurus.
When first named, Ceratosaurus was considered the sole member of the infraorder Ceratosauria. In 1892, Edward Drinker Cope reclassified it as a species of Megalosaurus. Subsequently classified as carnosaurs, coelurosaurs, deinodontids and megalosaurids, it was eventually found that the Ceratosauria was a valid clade, consisting of abelisaurs, ceratosaurs, elaphrosaurs, and noasaurs. It was once believed that Proceratosaurus was related to Ceratosaurus, on the basis of their shared nasal horn. Below is a cladogram showing the relationships of Ceratosaurus, after Pol & Rauhut (2012).
| Ceratosauria |
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Paleobiology[]
Ecology and feeding[]
Dry season at the Mygatt-Moore Quarry showing Ceratosaurus (center) and Allosaurus fighting over the desiccated carcass of another theropod
Within the Morrison Formation, Ceratosaurus fossils are frequently found in association with those of other large theropods, including the megalosaurid Torvosaurus and the allosaurid Allosaurus. The Garden Park locality in Colorado contained, besides Ceratosaurus, fossils attributed to Allosaurus. The Dry Mesa Quarry in Colorado, as well as the Cleveland-Lloyd Quarry and the Dinosaur National Monument in Utah, feature, respectively, the remains of at least three large theropods: Ceratosaurus, Allosaurus, and Torvosaurus. Likewise, Como Bluff and nearby localities in Wyoming contained remains of Ceratosaurus, Allosaurus, and at least one large megalosaurid. Ceratosaurus was a rare element of the theropod fauna; it is outnumbered by Allosaurus at an average rate of 7.5 to 1 in sites where they co-occur.
Several studies attempted to explain how these sympatric species could have reduced direct competition. Donald Henderson, in 1998, argued that Ceratosaurus co-occurred with two separate potential species of Allosaurus, which he denoted as "morphs": a morph with a shortened snout, a high and wide skull, and short, backwards-projecting teeth, and a morph characterized by a longer snout, lower skull, and long, vertical teeth. Generally speaking, the greater the similarity between sympatric species regarding their morphology, physiology, and behavior, the more intense competition between these species will be. Henderson came to the conclusion that the short-snouted Allosaurus morph occupied a different ecological niche from both the long-snouted morph and Ceratosaurus: The shorter skull in this morph would have reduced bending moments occurring during biting, thus increased bite force, comparable to the condition seen in cats. Ceratosaurus and the other Allosaurus morph, though, had long-snouted skulls, which are better compared to those of dogs: The longer teeth would have been used as fangs to deliver quick, slashing bites, with the bite force concentrated at a smaller area due to the narrower skull. According to Henderson, the great similarities in skull shape between Ceratosaurus and the long-snouted Allosaurus morph indicate that these forms engaged in direct competition with each other. Therefore, Ceratosaurus might had been pushed out of habitats dominated by the long-snouted morph. Indeed, Ceratosaurus is very rare in the Cleveland-Lloyd Quarry, which contains the long-snouted Allosaurus morph, but appears to be more common in both Garden Park and the Dry Mesa Quarry, in which it co-occurs with the short-snouted morph.
Reconstructed skeletons of Allosaurus and C. nasicornis in fighting postures, at Dinoworld Expo, Yokohama
Furthermore, Henderson suggested that Ceratosaurus could have avoided competition by preferring different prey items; the evolution of its extremely elongated teeth might have been a direct result of the competition with the long-snouted Allosaurus morph. Both species could also have preferred different parts of carcasses when acting as scavengers. The elongated teeth of Ceratosaurus could have served as visual signals facilitating the recognition of members of the same species, or for other social functions. In addition, the large size of these theropods would have tended to decrease competition, as the number of possible prey items increases with size.
Foster and Daniel Chure, in a 2006 study, concurred with Henderson that Ceratosaurus and Allosaurus generally shared the same habitats and preyed upon the same types of prey, thus likely had different feeding strategies to avoid competition. According to these researchers, this is also evidenced by different proportions of the skull, teeth, and fore limb. The distinction between the two Allosaurus morphs, however, was questioned by some later studies. Kenneth Carpenter, in a 2010 study, found that short-snouted individuals of Allosaurus from the Cleveland-Lloyd Quarry represent cases of extreme individual variation rather than a separate taxon. Furthermore, the skull of USNM 4734 from the Garden Park locality, which formed the basis for Henderson's analysis of the short-snouted morph, was later found to have been reconstructed too short.
In a 2004 study, Robert Bakker and Gary Bir suggested that Ceratosaurus was primarily specialized in aquatic prey such as lungfish, crocodiles, and turtles. As indicated by a statistical analysis of shed teeth from 50 separate localities in and around Como Bluff, teeth of both Ceratosaurus and megalosaurids were most common in habitats in and around water sources such as wet floodplains, lake margins, and swamps. Ceratosaurus also occasionally occurred in terrestrial localities. Allosaurids, however, were equally common in terrestrial and aquatic habitats. From these results, Bakker and Bir concluded that Ceratosaurus and megalosaurids must have predominantly hunted near and within water bodies, with Ceratosaurus also feeding on carcasses of larger dinosaurs on occasion. The researchers furthermore noted the long, low, and flexible body of Ceratosaurus and megalosaurids. Compared to other Morrison theropods, Ceratosaurus showed taller neural spines on the foremost tail vertebrae, which were vertical rather than inclined towards the back. Together with the deep chevron bones on the underside of the tail, they indicate a deep, "crocodile-like" tail possibly adapted for swimming. On the contrary, allosaurids feature a shorter, taller, and stiffer body with longer legs. They would have been adapted for rapid running in open terrain and for preying upon large herbivorous dinosaurs such as sauropods and stegosaurs, but as speculated by Bakker and Bir, seasonally switched to aquatic prey items when the large herbivores were absent. However, this theory was challenged by Yun in 2019, suggesting Ceratosaurus was merely more capable of hunting aquatic prey than other theropods of the Morrison Formation then its contemporaries as opposed to being fully semiaquatic.
Restoration of a feeding C. nasicornis
In his 1986 popular book The Dinosaur Heresies, Bakker argued that the bones of the upper jaw were only loosely attached to the surrounding skull bones, allowing for some degree of movement within the skull, a condition termed cranial kinesis. Likewise, the bones of the lower jaw would have been able to move against each other, and the quadrate bone to swing outwards, spreading the lower jaw at the jaw joint. Taken together, these features would have allowed the animal to widen its jaws in order to swallow large food items. In a 2008 study, Casey Holliday and Lawrence Witmer re-evaluated similar claims made for other dinosaurs, concluding that the presence of muscle-powered cranial kinesis cannot be proven for any dinosaur species, and was likely absent in most.
Function of the nasal horn and osteoderms[]
In 1884, Marsh considered the nasal horn of Ceratosaurus to be a "most powerful weapon" for both offensive and defensive purposes, and Gilmore, in 1920, concurred with this interpretation. The use of the horn as a weapon is now generally considered unlikely, however. In 1985, David Norman believed that the horn was "probably not for protection against other predators," but might instead have been used for intraspecific combat among male ceratosaurs contending for breeding rights. Gregory S. Paul, in 1988, suggested a similar function, and illustrated two Ceratosaurus engaged in a nonlethal butting contest. In 1990, Rowe and Gauthier went further, suggesting that the nasal horn of Ceratosaurus was "probably used for display purposes alone" and played no role in physical confrontations. If used for display, the horn likely would have been brightly colored. A display function was also proposed for the row of osteoderms running down the body midline.
Forelimb function[]
Cast of the hand of C. nasicornis (AMNH 27631): Most phalanges of the fingers are missing.
The strongly shortened metacarpals and phalanges of Ceratosaurus raise the question whether the manus retained the grasping function assumed for other basal theropods. Within the Ceratosauria, an even more extreme manus reduction can be observed in abelisaurids, where the forelimb lost its original function, and in Limusaurus. In a 2016 paper on the anatomy of the Ceratosaurus manus, Carrano and Jonah Choiniere stressed the great morphological similarity of the manus with those of other basal theropods, suggesting that it still fulfilled its original grasping function, despite its shortening. Although only the first phalanges are preserved, the second phalanges would have been mobile, as indicated by the well-developed articular surfaces, and the digits would likely have allowed a similar degree of motion as in other basal theropods. As in other theropods other than abelisaurids, digit I would have been slightly turned in when flexed.
Brain and senses[]
Juvenile skull in multiple views
A cast of the brain cavity of the holotype was made under Marsh's supervision, probably during preparation of the skull, allowing Marsh to conclude that the brain "was of medium size, but comparatively much larger than in the herbivorous dinosaurs". The skull bones, however, had been cemented together afterwards, so the accuracy of this cast could not be verified by later studies. A second, well preserved braincase had been found with specimen MWC 1 in Fruita, Colorado, and was CT-scanned by paleontologists Kent Sanders and David Smith, allowing for reconstructions of the inner ear, gross regions of the brain, and cranial sinuses transporting blood away from the brain. In 2005, the researchers concluded that Ceratosaurus possessed a brain cavity typical for basal theropods, and similar to that of Allosaurus. The impressions for the olfactory bulbs, which house the sense of smell, are well-preserved. While similar to those of Allosaurus, they were smaller than in Tyrannosaurus, which is thought to have been equipped with a very keen sense of smell. The semicircular canals, which are responsible for the sense of balance and therefore allow for inferences on habitual head orientation and locomotion, are similar to those found in other theropods. In theropods, these structures are generally conservative, suggesting that functional requirements during locomotion have been similar across species. The foremost of the semicircular canals was enlarged, a feature generally found in bipedal animals. The orientation of the lateral semicircular canal indicates that the head and neck were held horizontally in neutral position.
Fusion of metatarsals and paleopathology[]
The holotype of C. nasicornis was found with its left metatarsals II to IV fused together. Marsh, in 1884, dedicated a short article to this at the time unknown feature in dinosaurs, noting the close resemblance to the condition seen in modern birds. The presence of this feature in Ceratosaurus became controversial in 1890, when Georg Baur speculated that the fusion in the holotype was the result of a healed fracture. This claim was repeated in 1892 by Cope, while arguing that C. nasicornis should be classified as a species of Megalosaurus due to insufficient anatomical differences between these genera. However, examples of fused metatarsals in dinosaurs that are not of pathological origin have been described since, including taxa more basal than Ceratosaurus. Osborn, in 1920, explained that no abnormal bone growth is evident, and that the fusion is unusual, but likely not pathological. Ronald Ratkevich, in 1976, argued that this fusion had limited the running ability of the animal, but this claim was rejected by Paul in 1988, who noted that the same feature occurs in many fast-moving animals of today, including ground birds and ungulates. A 1999 analysis by Darren Tanke and Bruce Rothschild suggested that the fusion was indeed pathological, confirming the earlier claim of Baur. Other reports of pathologies include a stress fracture in a foot bone assigned to the genus, as well as a broken tooth of an unidentified species of Ceratosaurus that shows signs of further wear received after the break.
Paleoenvironment and paleobiogeography[]
Ceratosaurus in its environment.
Ceratosaurus lived with Allosaurus and Torvosaurus as well as similar animals in the Morrison Formation. Inter species conflict between Ceratosaurus and Allosaurus is apparent, however this is disputed between scientists. Fossils of Ceratosaurus teeth marks on Allosaurus foot bones show that the two species often attacked each other. Ceratosaurus has a large horn on its snout, the use of which is unknown.
Ecologically, Ceratosaurus and the more famous Allosaurus are quite interesting. The short-snouted species of the former, Allosaurus fragilis, concentrated its bite force into a smaller area and likewise specialized in producing stabbing wounds (likened to felids), occupying a different niche. The long-snouted Allosaurus jimmadseni, however, probably occupied a similar niche to Ceratosaurus (likened to canids). In 1998, Donald Henderson proposed that A. jimmadseni outcompeted Ceratosaurus in most areas, contributing to its rarity. Areas where jimmadseni were rare, such as Garden Park and the Dry Mesa Quarry, were ruled by Ceratosaurus.
Henderson also suggested that Ceratosaurus evolved to occupy a different niche to its competitor and that its enlarged teeth evolved for this purpose. However, a problem was eventually found with this theory. The Allosaurus illustrations that Henderson used as references portrayed the shout as being shorter than it really was. This, unfortunately, means that the very basis of Henderson's idea, one that otherwise appears relatively sound, is entirely invalid.
In 2004, Robert Bakker and Gary Bir suggested that Ceratosaurus was a specialist hunter of aquatic prey, such as lungfish, crocodiles and turtles, one of their arguments being that the tail may have been used as a sculling organ. This idea is presumably based on the vaguely-crocodilian cross-section of Ceratosaurus' tail, and the presence of Ceratosaurus teeth in rock layers where lungfish fossils are abundant. However, there is no good evidence to support this. As stated by Naish and Barrett in a 2018 book: "Yes, Ceratosaurus may well have been a good swimmer, and yes, it may have well shed its teeth after feeding on lungfish on occasion, but it lacks other features of the skeleton suited for life in water." In short, Ceratosaurus was maladapted to an aquatic lifestyle in most respects. Indeed, in 2019, it was suggested that Ceratosaurus was merely more well-adapted to hunting prey than other Morrison theropods, rather than being fully semiaquatic. Massive specimens are known from the Dry Mesa Dinosaur Quarry.
JPInstitute.com Description[]
Ceratosaurus was a medium sized meat-eater that lived at the same time as the larger Allosaurus in the last part of the Jurassic Period. What makes it different and distinctive is the large horn on top of its nose and the two horns over its eyes. About 100 years ago, when it was first discovered, it was one of the most well-known dinosaurs. Another unusual feature is that Ceratosaurus had four fingers on its hands, instead of the more common three among the other large meat-eaters.
Recently, the classification for Ceratosaurus has been questioned. It is being considered by some to be more closely associated with Carnosauria that Ceratosauria. An interesting footnote is that the Nanotyrannus type specimen was thought to be a Ceratosaurus when it was first being prepared.
Dinosaur Field Guide Description[]
Ceratosaurus ("horned lizard) was one of the first meat-eating dinosaurs known from a nearly complete skeleton. The first Ceratosaurus was found in 1883 in the Garden Park Quarry of Canyon City, Colorado. This area has produced many of the most important Jurassic fossils known. Although some parts of the arms and legs were missing, the rest of the skeleton was almost complete. Before this discovery, no skeleton of a large meat-eating dinosaur had been found that was more than half complete. These bones gave paleontologists many of their first insights into predatory dinosaurs. Ceratosaurus was unusual for a meat-eater that it had a horn on its nose. The horn was very thin side-to-side (unlike the horns of the plant-eaters like Centrosaurus and Triceratops, which were cone-shaped). This horn, and the smaller horns just in front of its eyes, were very delicate and probably used only for signaling to other Ceratosaurus. The huge teeth and powerful jaws were probably Centrosaurus's main weapons, since its arms and claws were small and feeble.
Fun Facts[]
Although it was smaller overall than Allosaurus, Ceratosaurus had bigger teeth than its rival.
Trivia[]
The horns on the nose and in front of the eyes of Ceratosaurus got bigger as the dinosaur got older.
Gallery[]
Appearance in other media[]
Jurassic Park[]
- Ceratosaurus appears briefly in Jurassic Park 3 when the main characters are looking for a satellite phone in a pile of Spinosaurus dung. Like all of InGen's cloned theropods, Ceratosaurus had pronated wrists and a thin frame. The clones also had small horns over the eyes like a Ceratosaurus juvenile and was slightly larger than the original with the most notable difference in size being that it was 3 meters in height rather than 2 meters. This was originally supposed to be Carnotaurus, but it was changed to Ceratosaurus.
- Ceratosaurus, though not on screen, fell back into extinction after the Isla Nublar Incident of 2015 before Jurassic World: Fallen Kingdom.
- Ceratosaurus was added to Jurassic World: The Game on January 22, 2016 as a limited tournament dinosaur. It is a legendary carnivore. It has three long finger rather than the four short ones the real animal had.
- Ceratosaurus is one of the available dinosaurs in the IOS application, Jurassic Park: Builder.
- The Ceratosaurus also appears in Jurassic World: Evolution, seen in the second in-game trailer footage. It looks a lot like the Jurassic Park III movie version, with a red at the head with black marks and white body. However, it takes more after its real-life counterpart, including a thinner skull with more prominent brow horns.
- Ceratosaurus is featured in the DVD game Jurassic Park: Explorer. A player earns the dinosaur when he/she wins a minigame. It is stated that Ceratosaurus was a cousin to Allosaurus, when actually both dinosaurs are distantly related.
- Ceratosaurus is available as a two-star, small carnivore in the game Jurassic Park: Operation Genesis. Its appearance is based on the movie. However, Ceratosaurus‘ upper jaw is actually smaller than the movie's design. Ceratosaurus hunts larger herbivores in packs or even by itself for that matter. It is known to posses cannibalism when no other food is around. Ceratosaurus can coexist with the Albertosaurus, Dilophosaurus and Allosaurus (though they do fear it and flee when it is near) and even with smaller carnivores like Velociraptor, but this only occurs when they are not hungry or attacking each other. However with the smaller carnivores like Velociraptor the Ceratosaurus coexists either way and can even share its meals among the smaller theropods.
- Ceratosaurus can be created in Jurassic Park III: Park Builder.
- Ceratosaurus appear in the second, third, fourth and fifth season of Jurassic World: Camp Cretaceous.
- Ceratosaurus appear in the game Jurassic World: Alive in the 2,23 Update after being requested by fans for a long time. It is one of the two unique non-hybrid dinosaur alongside Dracovenator.
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Read more Ceratosaurus on Jurassic Park Wiki |
The Land Before Time[]
- Ceratosaurus appeared in The Land Before Time: Preschool Adventure.
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Read more Ceratosaurus on Land Before Time Wiki |
We're Back! A Dinosaur's Story[]
- Bootsy from Your Pet Dinosaur: An Owner's Manual is a purple Ceratosaurus.
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Links[]
References[]
- https://www.researchgate.net/publication/272152335_Ceratosaurus_Dinosauria_Theropoda_a_revised_osteology
- https://www.researchgate.net/publication/262223836_New_evidence_of_Ceratosaurus_Dinosauria_Theropoda_from_the_Late_Jurassic_of_the_Lusitanian_Basin_Portugal
- https://www.researchgate.net/publication/334560612_Comments_on_the_ecology_of_Jurassic_theropod_dinosaur_Ceratosaurus_Dinosauria_Theropoda_with_critical_reevaluation_for_supposed_semiaquatic_lifestyle
- https://www.researchgate.net/publication/260793857_Ceratosaurus_sp_Dinosauria_Theropoda_in_the_Late_Jurassic_of_Portugal
- https://www.researchgate.net/publication/326017886_Ceratosaur_palaeobiology_New_insights_on_evolution_and_ecology_of_the_southern_rulers
- https://www.researchgate.net/publication/343285737_Ceratosaurus_Theropoda_Ceratosauria_teeth_from_the_Tacuarembo_Formation_Late_Jurassic_Uruguay
- https://www.jstor.org/stable/24740280