Temporal range: Late Jurassic, 153–148 Ma
|Cast of Ceratosaurus from the Cleveland Lloyd Quarry, on display at the Natural History Museum of Utah|
Ceratosaurus // (from Greek κερας/κερατος, keras/keratos meaning "horn" and σαυρος/sauros meaning "lizard"), was a large predatory theropod dinosaur from the Late Jurassic Period (Kimmeridgian to Tithonian), found in the Morrison Formation of North America, and the Lourinhã Formation of Portugal (and possibly the Tendaguru Formation in Tanzania). It was characterized by large jaws with blade-like teeth, a large, blade-like horn on the snout and a pair of hornlets over the eyes. The forelimbs were powerfully built but very short. The bones of the sacrum were fused (synsacrum) and the pelvic bones were fused together and to this structure (i.e. similar to modern birds). A row of small osteoderms was present down the middle of the back.
Ceratosaurus followed the bauplan typical for large theropod dinosaurs. A biped, it moved on powerful hind legs, while its arms were reduced in size. The holotype specimen was an individual about 5.3 metres (17 ft) long; it is not clear whether this animal was fully grown. Marsh (1884) suggested that the holotype individual weighed about half as much as Allosaurus. In more recent accounts, it was estimated at 418 kilograms (922 lb), 524 kilograms (1,155 lb) and 670 kilograms (1,480 lb) by separate authors. Two skeletons, assigned to the new species C. magnicornis and C. dentisulcatus by James H. Madsen and Samuel P. Welles in a 2000 monograph, were substantially larger than the holotype. The larger of these, C. dentisuclatus, was informally estimated by Madsen to have been around 8.8 metres (29 ft) long. American science writer Gregory S. Paul, in 1988, estimated the C. dentisulcatus specimen at 980 kilograms (2,160 lb). A considerably lower figure, 275 kilograms (606 lb) for C. magnicornis and 452 kilograms (996 lb) for C. dentisulcatus, was proposed by John Foster in 2007.
The skull was quite large in proportion to the rest of its body, measuring 62.5 cm 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 specimen, the horn core is 13 centimetres (5.1 in) long and 2 centimetres (0.79 in) wide at its base but quickly narrows down to only 1.2 centimetres (0.47 in) further up; it is 7 centimetres (2.8 in) in height. The horn core formed from co-ossified protuberances of the left and right paired 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 hornlike ridges in front of each eye, similar to those of Allosaurus; these ridges were formed by the paired lacrimal bones. All three horns were larger in adults than in juveniles.
The upper jaws were lined with between 12 and 15 blade-like teeth on each side. The paired premaxillary bone, which formed the tip of the snout, contained merely three teeth on each half, less than in most other theropods. Each half of the lower jaw was equipped with 11 to 15 teeth that were slightly straighter and less sturdy than those of the upper jaw. The tooth crowns of the upper jaw were exceptionally long, measuring up to 9.3 cm in length in the largest specimen, which is equal to the minimum height of the lower jaw. In the smaller holotype specimen, the length of the upper tooth crowns (7 cm) even surpasses the minimum height of the lower jaw (6.3 cm) – in other theropods, this feature is only known from the possibly closely related Genyodectes. In contrast, several members of the related Abelisauridae feature very low tooth crowns.
The exact number of vertebrae is unknown due to several gaps in the holotype's spine. The sacrum consisted of 6 fused sacral vertebrae. At least 20 presacral vertebrae formed the spine of the neck and back and ca. 50 caudal vertebrae the tail. The tail comprised about half of the body's total length; as in other dinosaurs, it counterbalanced the body and contained the massive caudofemoralis muscle, which was responsible for forward thrust during locomotion, pulling the upper tigh backwards when contracted. The tail of Ceratosaurus was characterized by comparatively high neural spines (upwards directed bony processes of the caudal vertebrae) and elongated chevrons (bones located below the tail vertebrae), giving the tail a deep profile in lateral view. Uniquely among theropods, Ceratosaurus possessed a row of small, elongated and irregularly formed osteoderms (skin bones) running down the middle of its neck, back and most of its tail. Apart from the body midline, the skin contained additional osteoderms, as indicated by a 6 × 7 cm large plate found together with the holotype specimen; the position of this plate on the body is unknown.
History of discovery
The first specimen, the holotype specimen USNM 4737, was discovered by the farmer Marshall Parker Felch in 1883 to 1884. An articulated skeleton (with bones still in their original anatomical position), it was nearly complete, including the skull. The specimen was found encased in hard sandstone; 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 one of the richest fossil sites of the Morrison Formation. Numerous dinosaur fossils had been rescued from this quarry even before the discovery of Ceratosaurus, most notably the holotype specimen of Allosaurus. Shortly after its discovery, paleontologist Othniel Charles Marsh published a description of the skeleton, naming the new genus and species Ceratosaurus nasicornis. Given the completeness of the specimen, the newly described genus was the at the time best-known theropod discovered in America. The name Ceratosaurus ("Horn lizard"; from Greek κερας/κερατος, keras/keratos meaning "horn" and σαυρος/sauros meaning "lizard") alludes to the animal's prominent nose horn. In 1920, paleontologist Charles Gilmore published an extensive re-description of the skeleton.
In a 1892 paper, Marsh published the first skeletal reconstruction of Ceratosaurus. As noted by Gilmore in 1920, the trunk was depicted much too long in this reconstruction, incorporating at least six supernumerary dorsal vertebrae. 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 J. M. Gleeson, again under Knight's supervision. The holotype specimen was mounted by Gilmore in 1910 and 1911 and since was on exhibit at the National Museum of Natural History in Washington, D.C.. Because of the strong flattening of the fossils, Gilmore mounted the specimen not as free-standing skeleton but as a basrelief. Most early reconstructions show Ceratosaurus in an upright posture, with the tail dragged over the ground. Gilmore's mount, 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 which did not make contact with the ground.
After the discovery of the holotype skeleton, a significant find was not made until the early 1960's, when paleontologist James Madsen and his team unearthed a fragmentary, disarticulated skeleton including the skull (specimen number UMNH VP 5278) in the Cleveland-Lloyd Dinosaur Quarry in Utah. This find represents the largest known Ceratosaurus specimen. A second, articulated specimen including the skull (specimen number MWC 1) was discovered by Thor Erikson, the son of paleontologist Lance Erikson, in 1976 near Fruita, Colorado. A fairly complete specimen, it lacks lower jaws, forearms and gastralia. It was a large, but not fully grown individual, as indicated by open sutures between the skull bones. Both specimens were described by Madsen and Samuel Paul Welles in a 2000 monograph, with the Utah specimen being referred to the new species Ceratosaurus dentisulcatus and the Colorado specimen to the new species Ceratosaurus magnicornis. The validity of both species, however, was questioned in subsequent publications. A further specimen (specimen number BYUVP 12893) was discovered in 1992 in the Agate Basin Quarry in Utah, but still awaits description. The specimen, one of the largest Ceratosaurus specimens known, includes the front half of a skull, seven fragmentary pelvic dorsal vertebrae, and fragmentary pelvic bones. In 1999, paleontologist Brooks Britt reported the discovery of the first Ceratosaurus skeleton pertaining to a juvenile individual. Discovered in Bone Cabin Quarry in Wyoming, it is 34% smaller than the holotype specimen 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 bone (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 of North America
In the years 1909 to 1913, German expeditions of the Berlin Museum für Naturkunde brought to light a diverse dinosaur fauna from the Tendaguru Formation in German East Africa, today 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 referred several dorsal vertebrae from the quarry "TL" to Ceratosaurus, as Ceratosaurus sp. (of uncertain species). In 1925, Janensch named a new species of Ceratosaurus, Ceratosaurus 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 Ceratosaurus holotype individual. Madsen and Welles, in their 2000 monography, confirmed the referral of these finds to Ceratosaurus, and additionally ascribed several teeth to the genus which had originally been described by Janensch as Labrosaurus (?) stechowi. Other authors question the referral of any of the Tendaguru finds to Ceratosaurus, noting that none of these specimens displays features diagnostic for that genus. Ceratosaurus ingens is now believed to be a dubious carcharodontosaurid, and Labrosaurus(?) stechowi probably represents a taxon closely related to Ceratosaurus. In 1990, Rowe and Gauthier mention a second Ceratosaurus species from Tendaguru, Ceratosaurus ingens, which purportedly was erected by Janensch in 1920 and is based on 25 isolated, very large teeth up to 15 cm in length. Janensch, however, did in fact not refer this species to Ceratosaurus but to Megalosaurus; this name therefore might be a simple copying error.
In 2000 and 2006, Paleontologists around Octávio Mateus described a find from the Lourinhã Formation in Portugal as a new specimen of Ceratosaurus, consisting of an upper thigh bone, a shin bone, and several isolated teeth. The specimen provides evidence of a Portuguese theropod fauna similar in composition to the North American Morrison Formation: Besides Ceratosaurus, the researchers also noted the presence of Allosaurus and Torvosaurus in the Portuguese rocks. During the Late Jurassic, Europe had just been separated from North America by the still narrow Atlantic Ocean, and Portugal, as part of the Iberian Peninsula, was still separated from other parts of Europe. The similarity between the Portuguese and North American theropod fauna indicates the presence of a temporary land bridge, allowing for faunal interchange. The specimen was ascribed to the species Ceratosaurus dentisulcatus by Mateus and colleagues. A later review by Carrano and Sampson (2008) confirmed the referral to Ceratosaurus, but concluded that the referral to a specific species is not possible at present.
Other reports include a single tooth found in Moutier, Switzerland. Originally named by Janensch in 1920 as Labrosaurus meriani, the tooth was later referred Ceratosaurus sp. (of unknown species) by Madsen and Welles. Soto and Perea, in 2008, described teeth from the Tacuarembó Formation in Uruguay that show features diagnostic for Ceratosaurus. These authors, however, stress that a referral to Ceratosaurus is infeasible due to the scant remains, and note that the referral of the European and African Material to Ceratosaurus has to be viewed with caution.
Definition and species
According to Rauhut (2000), Ceratosaurus can be distinguished from related genera based on the following features: a narrow rounded horn core centrally placed on the fused nasals, a median oval groove on nasals behind horn core, a premaxilla with three teeth, premaxillary teeth with reduced extent of mesial serrations, chevrons that are extremely long, a pubis with a large, rounded notch underneath the obturator foramen, small epaxial osteoderms.
Only the type species Ceratosaurus nasicornis is universally accepted as valid. Two additional species, Ceratosaurus magnicornis and Ceratosaurus dentisulcatus, were named by Madsen and Welles (2000) based on specimens significantly larger than the Ceratosaurus nasicornis holotype. The validity of both species is disputed: Britt and colleagues, in 2000, claim that the Ceratosaurus nasicornis holotype is in fact a juvenile individual, with the two larger species representing the adult state of a single species. Rauhut (2003) and Carrano and Sampson (2008) consider the anatomical differences cited by Madsen and Welles to support these additional species to represent ontogenetic (age related) or individual variation.
Ceratosaurus is the eponymous member of the Ceratosauria, a major clade of non-avian theropod dinosaurs. The Ceratosauria splitted of early from the evolutionary line leading to modern birds, and thus is considered basal within theropods. Ceratosauria itself contains a group of derived members, such as Carnotaurus and Noasaurus, 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 ceratosaurs is under debate. Some analyses consider Ceratosaurus as the most derived of basal Ceratosauria, forming the sister taxon of Abelisauroidea. Oliver Rauhut, in 2004, however proposes 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 inside the family Ceratosauridae, which was followed by several later accounts. The Ceratosauridae had already been erected by Marsh in 1884, but contained Ceratosaurus as the only species and therefore was considered redundant and not used.
A skull from the Middle Jurassic of England apparently displays a nasal horn similar to that of Ceratosaurus. In 1926, Friedrich von Huene described this skull as Proceratosaurus (meaning "before-Ceratosaurus"), assuming that it was an antecedent of the Late Jurassic Ceratosaurus. Today, Proceratosaurus is considered a basal member of the Tyrannosauroidea, a much more derived clade of theropod dinosaurs; the nasal horn therefore would have evolved independently in both genera. Oliver Rauhut and colleagues, in 2010, grouped Proceratosaurus within its own family, Proceratosauridae. These authors also noted that the nasal horn is incompletely preserved, opening the possibility that it represented the foremost portion of a more extensive head crest, as seen in some other proceratosaurids such as Guanlong.
Ceratosaurus lived alongside dinosaurs such as Allosaurus, Torvosaurus, Apatosaurus, Diplodocus, Stegosaurus and Camarasaurus. Ceratosaurus reached lengths of 6.7 m (22 ft), and weighed up to 980 kilograms (2,160 lb). It was smaller than the other large carnivores of its time (allosaurs and Torvosaurus) and likely occupied a distinctly separate niche from them. Ceratosaurus fossils are noticeably less common than those of Allosaurus, but whether this implies Ceratosaurus being rarer is uncertain (animals with certain lifestyles are more biased toward fossilization than others). Ceratosaurus had a longer, more flexible body, with a deep tail shaped like that of a crocodilian. This suggests that it was a better swimmer than the stiffer Allosaurus. A recent study by Robert Bakker suggested that Ceratosaurus generally hunted aquatic prey, such as fish and crocodiles, although it had potential for feeding on large dinosaurs. The study also suggests that sometimes adults and juveniles ate together. This evidence is debatable, and Ceratosaurus tooth marks are very common on large, terrestrial dinosaur prey fossils. Scavenging from corpses, smaller predators, and after larger ones also likely accounted for some of its diet.
Ceratosaurus, Allosaurus and Torvosaurus appear to have had different ecological niches, based on anatomy and the location of fossils. Ceratosaurus and Torvosaurus may have preferred to be active around waterways, and had lower, thinner bodies that would have given them an advantage in forest and underbrush terrains, whereas Allosaurus were more compact, with longer legs, faster but less maneuverable, and seem to have preferred dry floodplains. Ceratosaurus, better known than Torvosaurus, differed noticeably from Allosaurus in functional anatomy by having a taller, narrower skull with large, broad teeth. Allosaurus was itself a potential food item to other carnivores, as illustrated by an Allosaurus pubic foot marked by the teeth of another theropod, probably Ceratosaurus or Torvosaurus. The location of the bone in the body (along the bottom margin of the torso and partially shielded by the legs), and the fact that it was among the most massive in the skeleton, indicates that the Allosaurus was being scavenged.
Marsh (1884) considered the nasal horn of Ceratosaurus to be a "most powerful weapon" for both offensive and defensive purposes, and Gilmore (1920) concurred with this analysis. However, this interpretation is now generally considered unlikely. Norman (1985) 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. Paul (1988) suggested a similar function, and illustrated two Ceratosaurus engaged in a non-lethal butting contest. Rowe and Gauthier (1990) 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, it is likely that the horn would have been brightly colored.
In 2001, Bruce Rothschild and others published a study examining evidence for stress fractures in theropod dinosaurs. They examined a single foot bone referred to Ceratosaurus and found that it had a stress fracture.
The holotype specimen of Ceratosaurus nasicornis, USMN 4735 was found with its left metatarsals II to IV fused together. Whether or not this fusion was pathological or natural to the species became controversial when Baur in 1890 speculated that the fusion was the result of a healed fracture. An analysis by Tanke and Rothschild suggests that the fusion was indeed pathological.
An unidentified species of Ceratosaurus preserved a broken tooth that showed signs of further wear received after the break.
The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according to radiometric dating, ranges between 156.3 million years old (Ma) at its base, and 146.8 million years old at the top, which places it in the late Oxfordian, Kimmeridgian, and early Tithonian stages of the Late Jurassic period. This formation is interpreted as a semiarid environment with distinct wet and dry seasons. The Morrison Basin where dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels, and floodplains. This formation is similar in age to the Lourinha Formation in Portugal and the Tendaguru Formation in Tanzania. In 1877, this formation became the center of the Bone Wars, a fossil-collecting rivalry between early paleontologists Othniel Charles Marsh and Edward Drinker Cope.
The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs. Other dinosaurs known from the Morrison include the theropods Koparion, Stokesosaurus, Ornitholestes, Allosaurus and Torvosaurus, the sauropods Apatosaurus, Brachiosaurus, Camarasaurus, and Diplodocus, and the ornithischians Camptosaurus, Dryosaurus, Othnielia, Gargoyleosaurus and Stegosaurus. Diplodocus is commonly found at the same sites as Apatosaurus, Allosaurus, Camarasaurus, and Stegosaurus. Allosaurus, which accounted for 70 to 75% of theropod specimens and was at the top trophic level of the Morrison food web. Many of the dinosaurs of the Morrison Formation are the same genera as those seen in Portuguese rocks of the Lourinha Formation (mainly Allosaurus, Ceratosaurus, Torvosaurus, and Stegosaurus), or have a close counterpart (Brachiosaurus and Lusotitan, Camptosaurus and Draconyx). Other vertebrates that shared this paleoenvironment included ray-finned fishes, frogs, salamanders, turtles like Dorsetochelys, sphenodonts, lizards, terrestrial and aquatic crocodylomorphans such as Hoplosuchus, and several species of pterosaur like Harpactognathus and Mesadactylus. Shells of bivalves and aquatic snails are also common. The flora of the period has been revealed by fossils of green algae, fungi, mosses, horsetails, cycads, ginkgoes, and several families of conifers. Vegetation varied from river-lining forests of tree ferns, and ferns (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.
In popular culture
Ceratosaurus has appeared in several films, including the first live action film to feature dinosaurs, D. W. Griffith's Brute Force (1914). In the Rite of Spring segment of Fantasia (1940), Ceratosaurus are shown as opportunistic predators attacking Stegosaurus and sauropods trapped in mud. In Unknown Island (1948). In The Animal World (1956) a Ceratosaurus kills a Stegosaurus in battle, but is soon attacked by another Ceratosaurus trying to steal a meal. This scene ends with both Ceratosaurus falling to their deaths off the edge of a high cliff.
A Ceratosaurus battles a Triceratops in the 1966 remake of One Million Years B.C.. Ceratosaurus is also featured in The Land That Time Forgot (1975) where it battles a Triceratops, and its sequel The People That Time Forgot (1977) in which Patrick Wayne's character rescues a cavegirl from two pursuing Ceratosaurus by driving the dinosaurs off with smoke bombs (after having failed to frighten them off by firing shots in the air once the Ceratosaurus' attention had been shifted to Patrick Wayne's party of explorers). A Ceratosaurus made a brief appearance in the film Jurassic Park III in which it is repelled from attacking the main characters by a large mound of Spinosaurus dung. This dinosaur also appears in the television documentary When Dinosaurs Roamed America, a Ceratosaurus makes a few appearances as a predator, killing Dryosaurus and eating it, a different one is shown chasing the same Dryosaurus but is then killed and eaten by an Allosaurus. Ceratosaurus is also featured in episodes of Jurassic Fight Club where it is seen as a rival to Allosaurus and preying on Stegosaurus.
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