Editing Ceratosaurus (section)

==Description==
[[File:Ceratosaurus Size Comparison by PaleoGeek.svg|thumb|right|alt=Scale chart comparing two specimens to a human<!--why is he wearing a top hat?-->|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]]

''Ceratosaurus'' followed the [[body plan]] typical for large theropod dinosaurs.<ref name="marsh-92"/> As a [[Bipedalism|biped]], it moved on powerful legs, while its arms were reduced in size. Specimen USNM 4735, the first discovered skeleton and [[holotype]] of ''Ceratosaurus nasicornis'', was an individual {{convert|5.3|m|abbr=on}} or {{convert|5.69|m|abbr=on}} long according to separate sources.<ref name="gilmore-20"/>{{rp|115}}<ref name="paul_1988"/> Whether this animal was fully grown is unclear.<ref name="tykoski-et-al-04"/>{{rp|66}} [[Othniel Charles Marsh]], in 1884, suggested that this specimen weighed about half as much as the contemporary ''[[Allosaurus]]''.<ref name="marsh-84"/> In more recent accounts, this was revised to {{convert|418|kg|lb}}, {{convert|524|kg|abbr=on}}, or {{convert|670|kg|abbr=on}}.<ref name="therrien2007"/> Three additional skeletons discovered in the latter half of the 20th century were substantially larger. The first of these, UMNH VP 5278, was estimated by [[James Henry Madsen|James Madsen]] to have been around {{convert|8.8|m|abbr=on}} long,<ref name="glut-97"/> but was later estimated at {{convert|7|m|abbr=on}} long.<ref name="paul2016"/> Its weight was calculated at {{convert|980|kg|abbr=on}}, {{convert|452|kg|sigfig=3|abbr=on}}, and {{convert|700|kg|sigfig=3|abbr=on}} in separate works.<ref name="paul_1988"/><ref name="paul2016"/><ref name="foster-07"/> The second skeleton, MWC 1, was somewhat smaller than UMNH VP 5278 and might have weighed {{convert|275|kg|sigfig=3|abbr=on}}.<ref name="foster-07" /> The third, yet undescribed, specimen BYUVP 12893 was claimed to be the largest yet discovered, although estimates have not been published.<ref name="carrano2008" />{{rp|192}} Another specimen, ML 352, discovered in Portugal in 2000, was estimated at {{convert|6|m|abbr=on}} in length and {{convert|600|kg|sigfig=3|abbr=on}}.<ref name="paul2016"/>

===Skull===
[[file:Osteology of the carnivorous Dinosauria in the United States National museum BHL40623209 edited.jpg|thumb|left|alt=Charles Gilmore's reconstruction of the skull in side and top view |Diagram of the ''Ceratosaurus nasicornis'' holotype skull in top and side view by [[Charles W. Gilmore|Charles Gilmore]], 1920: This reconstruction is now thought to be too wide in top view.]]
The [[skull]] was quite large in proportion to the rest of its body.<ref name="marsh-92"/> It measures {{convert|55|cm|abbr=on}} in length in the ''C. nasicornis'' holotype, measured from the tip of the snout to the {{dinogloss|occipital condyle}}, which connects to the first cervical vertebra.<ref name="gilmore-20"/>{{rp|88}} The width of this skull is difficult to reconstruct, as it is heavily distorted, and Gilmore's 1920 reconstruction was later found to be too wide.<ref name="henderson1998"/> The fairly complete skull of specimen MWC 1 was estimated to have been {{convert|60|cm|abbr=on}} long and {{convert|16|cm|abbr=on}} wide. This skull was somewhat more elongated than that of the holotype.<ref name="madsen2000"/>{{rp|3}} The back of the skull was more lightly built than in some other larger theropods due to extensive skull openings, yet the jaws were deep to support the proportionally large teeth.<ref name="paul_1988"/>{{rp|277}} The [[lacrimal bone]] formed not only the back margin of the [[antorbital fenestra]], a large opening between eye and {{dinogloss|bony nostril}}, but also part of its upper margin, unlike in members of the related [[Abelisauridae]]. The [[quadrate bone]], which was connected to the lower jaw at its bottom end to form the jaw joint, was inclined so that the jaw joint was displaced backwards in relation to the occipital condyle. This also led to a broadening of the base of the [[Infratemporal fenestra|lateral temporal fenestra]], a large opening behind the eyes.<ref name="tykoski-et-al-04"/>{{rp|53}}

The most distinctive feature was a prominent horn situated on the skull midline behind the bony nostrils, which was formed from fused protuberances of the left and right [[nasal bone]]s.<ref name="gilmore-20"/>{{rp|82}} Only the bony horn core is known from fossils. In the living animal, this core would have supported a [[keratin]]ous sheath. While the base of the horn core was smooth, its upper two-thirds were wrinkled and lined with grooves that would have contained [[blood vessel]]s when alive. In the holotype, the horn core is {{convert|13|cm|abbr=on}} long and {{convert|2|cm|abbr=on}} wide at its base, but quickly narrows to only {{convert|1.2|cm|abbr=on}} further up, and is {{convert|7|cm|abbr=on}} in height.<ref name="gilmore-20"/>{{rp|82}} It is longer and lower in the skull of MWC 1.<ref name="madsen2000"/>{{rp|3}} In the living animal, the horn would likely have been more elongated due to its keratinous sheath.<ref name="delcourt2018"/> Behind the nasal horn, the nasal bones formed an ovalur groove. Both this groove and the nasal horn serve as [[autapomorphy|features to distinguish]] ''Ceratosaurus'' from related genera.<ref name="carrano2008"/>{{rp|192}} In addition to the large nasal horn, ''Ceratosaurus'' possessed smaller, semicircular, bony ridges in front of each eye, similar to those of ''Allosaurus''. These ridges were formed by the lacrimal bones.<ref name="foster-07"/> In juveniles, all three horns were smaller than in adults and the two halves of the nasal horn core were not yet fused.<ref name="britt1999"/>

[[File:Ceratosaurus nasicornis (cast) - AMNH - DSC06292.JPG|thumb|alt=Cast of the skull of the holotype|Cast of the skull of the ''C. nasicornis'' holotype, showing the large nasal horn, [[American Museum of Natural History]]]]
The [[premaxillary bone]]s, which formed the tip of the snout, contained merely three teeth on each side, less than in most other theropods.<ref name="tykoski-et-al-04"/>{{rp|52}} The {{dinogloss|maxillary bones}} of the upper jaw were lined with 15 blade-like teeth on each side in the holotype. The first eight of these teeth were very long and robust, but from the ninth tooth onward, they gradually decrease in size. As is typical for theropods, they featured finely {{dinogloss|serrated}} edges, which contained some 10 [[Denticle (tooth feature)|denticles]] per {{convert|5|mm|abbr=on}} in the holotype.<ref name="gilmore-20" />{{rp|92}} Specimen MWC 1 merely showed 11 to 12 and specimen UMNH VP 5278 showed 12 teeth in each maxilla. The teeth were more robust and more recurved in the latter specimen.<ref name="madsen2000" />{{rp|3,27}} In all specimens, the [[tooth crown]]s of the upper jaws were exceptionally long. In specimen UMNH VP 5278, they measured up to {{convert|9.3|cm|abbr=on}} long, which is equal to the minimum height of the lower jaw. In the holotype, they are {{convert|7|cm|abbr=on}} in length, which even surpasses the minimum height of the lower jaw. In other theropods, a comparable tooth length is only known from the possibly closely related ''[[Genyodectes]]''.<ref name="rauhut2004"/> In contrast, several members of Abelisauridae feature very short tooth crowns.<ref name="tykoski-et-al-04"/>{{rp|92}} In the holotype, each half of the {{dinogloss|dentary}}, the tooth-bearing bone of the {{dinogloss|mandible}}, was equipped with 15 teeth, which are, however, poorly preserved. Both specimens MWC 1 and UMNH VP 5278 show only 11 teeth in each dentary, which were, as shown by the latter specimen, slightly straighter and less sturdy than those of the upper jaw.<ref name="madsen2000"/>{{rp|3,21}}

===Postcranial skeleton===
[[File:Ceratosaurus nasicornis DB.jpg|thumb|left|alt=Life reconstruction|Artist's impression of ''C. nasicornis'']]
The exact number of vertebrae is unknown due to several gaps in the spine of the ''Ceratosaurus nasicornis'' holotype. At least 20 vertebrae formed the neck and back in front of the [[sacrum]]. In the middle portion of the neck, the {{dinogloss|centra}} (bodies) of the vertebrae were as long as they were tall, while in the front and rear portions of the neck, the centra were shorter than their height. The upwards projecting {{dinogloss|neural spines}} were comparatively large and, in the dorsal (back) vertebrae, were as tall as the vertebral centra were long. The sacrum, consisting of six fused {{dinogloss|sacral vertebrae}}, was arched upwards, with its vertebral centra strongly reduced in height in its middle portion, as is the case in some other [[ceratosauria]]ns.<ref name="tykoski-et-al-04"/>{{rp|55–58}} The tail comprised around 50 {{dinogloss|caudal vertebrae}} and was about half of the animal's total length. In the holotype, it was estimated at {{convert|9.33|ft|abbr=on|order=flip}}.<ref name="marsh-84"/><ref name="gilmore-20"/>{{rp|115}} The tail was deep from top to bottom due to its high neural spines and elongated [[chevron (anatomy)|chevrons]], bones located below the vertebral centra. 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 thigh backwards when [[muscle contraction|contracted]].<ref name="tykoski-et-al-04"/>{{rp|55–58}}

[[File:Ceratosaurus jaw and nasale dinosaur journey museum fruita.jpg|thumb|upright|right|alt=Two skull bones (nasal and maxilla) on display Dinosaur Jurney Museum in Fruita, Colorado, showing distinctive anatomical features |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 [[scapula]] (shoulder blade) was fused with the [[coracoid]], forming a single bone without any visible demarcation between the two original elements.<ref name="tykoski-et-al-04"/>{{rp|58}} The ''C. nasicornis'' holotype was found with an articulated left arm including an incomplete hand. Although {{dinogloss|disarticulated}} during preparation, a cast had been made of the fossil beforehand to document the original relative positions of the bones. [[Carpal bones]] were not known from any specimen, leading some authors to suggest that they were lost in the genus. In a 2016 paper, Matthew Carrano and Jonah Choiniere suggested that one or more [[cartilage|cartilaginous]] (not bony) carpals were probably present, as indicated by a gap present between the forearm bones and the metacarpals, as well as by the surface texture within this gap seen in the cast.<ref name="carrano2016"/> In contrast to most more-[[Synapomorphy|derived]] theropods, which showed only three digits on each hand (digits I–III), ''Ceratosaurus'' retained four digits, with digit IV being reduced in size. The first and fourth [[metacarpus|metacarpals]] were short, while the second was slightly longer than the third. The metacarpus and especially the first [[Phalanx bone|phalanges]] were proportionally very short, unlike in most other [[basal (phylogenetics)|basal]] theropods. Only the first phalanges of digits II, III, and IV are preserved in the holotype. The total number of phalanges and [[ungual]]s (claw bones) is unknown. The anatomy of metacarpal I indicates that phalanges had originally been present on this digit as well. The [[pes (anatomy)|pes]] (foot) consisted of three weight-bearing digits, numbered II–IV. Digit I, which in theropods is usually reduced to a [[dewclaw]] that does not touch the ground, is not preserved in the holotype. Marsh, in his original 1884 description, assumed that this digit was lost in ''Ceratosaurus'', but [[Charles W. Gilmore|Charles Gilmore]], in his 1920 monograph, noted an attachment area on the second [[metatarsus|metatarsal]] demonstrating the presence of this digit.<ref name="gilmore-20"/>{{rp|112}}

Uniquely among theropods, ''Ceratosaurus'' possessed small, elongated, and irregularly formed [[osteoderm]]s (skin bones) along the midline of its body. Such osteoderms have been found above the neural spines of cervical vertebrae 4 and 5, as well as caudal vertebrae 4 to 10, and probably formed a continuous row that might have extended from the base of the skull to most of the tail. As suggested by Gilmore in 1920, their position in the rock matrix likely reflects their exact position in the living animal. The osteoderms above the tail were found separated from the neural spines by {{convert|25|mm|abbr=on}} to {{convert|38|mm|abbr=on}}, possibly accounting for skin and muscles present in between, while those of the neck were much closer to the neural spines. Apart from the body midline, the skin contained additional osteoderms, as indicated by a {{convert|58|mm|abbr=on}} by {{convert|70|mm|abbr=on}} large, roughly quadrangular plate found together with the holotype. The position of this plate on the body, however, is unknown.<ref name="gilmore-20"/>{{rp|113–114}} Specimen UMNH VP 5278 was also found with a number of osteoderms, which have been described as amorphous in shape. Although most of these {{dinogloss|ossicles}} were found at most 5 m apart from the skeleton, they were not directly associated with any vertebrae, unlike in the ''C. nasicornis'' holotype, so their original position on the body cannot be inferred from this specimen.<ref name="madsen2000"/>{{rp|32}}