{|class="palaeobox"
!''Ceratosaurus''
|-
|class="taxo-bild" | thumb|300px|''Ceratosaurus nasicornis''
|- 
! Zeitraum
|-
|class="taxo-zeit" | Jura
|-
|class="taxo-zeit" | 156 bis 145 Mio. Jahre 
|-
! Fossilfundorte
|-
| class="taxo-ort" | 
* Nordamerika (USA)
* Afrika (Tansania)
* Europa (Portugal)
|- 
! 
|-
|
 {|
  |-
  |Dinosaurier (Dinosauria)
  |-
  |Echsenbeckensaurier (Saurischia)
  |-
  |Theropoda
  |-
  |Ceratosauridae
 |}
|-
! Wissenschaftlicher Name
|-
| class="taxo-name" |''Ceratosaurus'' 
|-
| class="Person" | Marsh, 1884
|-
! en
|-
|
* ''Ceratosaurus dentisulcatus''
* ''Ceratosaurus magnicornis''
* ''Ceratosaurus roechlingi''
* ''Ceratosaurus nasicornis''
|-
|}

''' ''Ceratosaurus'' ''' („Horn-Echse“) war eine Gattung theropoder Dinosaurier aus dem Oberjura von Nordamerika, Europa und Afrika.

left|thumb|''Ceratosaurs'' im Größenvergleich
Die Gattung erreichte etwa fünf bis sechs Meter Länge und zwei Tonnen Gewicht. Sie war von ähnlicher Statur wie ''Allosaurus''. Über der Nase saß ein kleines Horn, dem er seinen Namen verdankt, über den Augen verliefen kleine knöcherne Höcker. Damit war sein Schädel schwerer als derjenige anderer Theropoden. In seinem Kiefer befanden sich gekrümmte Zähne. Anders als seine Verwandten trugen seine Arme vier bekrallte Finger; seine muskulösen Hinterbeine trugen ebenfalls vier Zehen. Eine weitere Besonderheit stellte eine Art niedriger Knochenkamm dar, der über den Rücken von ''Ceratosaurus'' verlief und bei keinem anderen Raubsaurier bekannt ist.

Der mögliche Nutzen dieser einzigartigen Merkmale von ''Ceratosaurus'' ist noch weitgehend unbekannt. Obwohl die Theorie, dass das Nasenhorn zum Kampf zwischen Rivalen benutzt worden sei, weit verbreitet ist, scheint sie nicht zuzutreffen, da das Horn für solche Kämpfe erstens zu klein und zweitens nicht ideal platziert war. Höchstwahrscheinlich diente es nur der Zurschaustellung.

Hingegen gilt als sicher, dass ''Ceratosaurus'' ein durchaus erfolgreicher Jäger war. Durch fossil erhaltene Fußabdrücke ist insbesondere belegt, dass er teilweise in Rudeln die größeren Sauropoden angriff.

Der erste Skelettfund von ''Ceratosaurus'' geht auf das Jahr 1884 zurück und wurde von Othniel Charles Marsh geleitet. Inzwischen sind weitere Funde aus den USA (Colorado, Utah, Wyoming) und Ostafrika bekannt.

{{Taxobox
|
| name = ''Ceratosaurus''
| fossil_range = Late Jurassic
| regnum = Animalia
| image = Ceratosaurusskeleton.jpg
| image_width = 250px
| image_caption = ''Ceratosaurus'' skeleton mount, Kelvingrove Art Gallery and Museum.
| phylum = Chordata
| classis = Sauropsida
| superordo = Dinosauria
| ordo = Saurischia
| subordo = Theropoda
| infraordo = Ceratosauria
| familia = Ceratosauridae
| genus = '''''Ceratosaurus'''''
| genus_authority = Marsh, 1884
| subdivision_ranks = Species
| subdivision = 
* ''C. nasicornis'' <small>(type)</small><br/><small>Marsh, 1884</small>
* ''C. ingens'' <br/><small>(Janensch, 1920)</small>
* ''C. dentisulcatus'' <br/><small>Madsen & Wells, 2000</small>
* ''C. magnicornis'' <br/><small>Madsen & Wells, 2000</small>
}}
'''''Ceratosaurus''''' () meaning 'horned lizard', in reference to the horn on its nose (Greek ''κερας/κερατος, keras/keratos'' meaning 'horn' and ''σαυρος''/''sauros'' meaning 'lizard'), was a large predatory Period, found in the Sereno 1997) (i.e. similar to modern birds). A row of small osteoderms was present down the middle of the back.<ref name=CWG20>Gilmore CW. 1920, Osteology of the Carnivorous Dinosauria in the United States National Museum. United States National Museum Bulletin. 110, pages 1-154</ref>

==Discovery and species==
thumb|left|''Ceratosaurus nasicornis'' fossil, North American Museum of Ancient Life. 
''Ceratosaurus'' is known from the O. C. Marsh in 1884 and redescribed by Gilmore in 1920, is ''Ceratosaurus nasicornis''.
Two further species were described in 2000,<ref> Madsen JH, Welles SP. Ceratosaurus (Dinosauria, Therapoda), a Revised Osteology. Miscellaneous Publication. Utah Geological Survey. ISBN 1-55791-380-3 </ref> ''C. magnicornis'', and ''dentisulcatus''. Both were more powerfully built, more derived, larger, and appeared in slightly younger rocks than ''C. nasicornis''. The Portuguese remains have recently been ascribed to ''C. dentisulcatus'' (Mateus et al 2006).
More additional species, including ''C. ingens'' and ''C. stechowi'', have been described from less complete material. If ''C. ingens'' is valid, then at least one species of ''Ceratosaurus'' was as large as ''Torvosaurus'' and ''Epanterias'' that lived alongside it.

''Ceratosaurus'' species:
*''C. nasicornis'' (type)
*''C. dentisulcatus''
*''C. magnicornis''
*''C. ingens
*''C. stechowi
*''C. meriani

==Paleobiology==
thumb|180px|left|Relative size of human and ''Ceratosaurus''.
''Ceratosaurus'' lived alongside dinosaurs such as ''Allosaurus'', ''Torvosaurus'', ''Apatosaurus'', ''Diplodocus'', and ''Stegosaurus''. It may have competed with ''Allosaurus'' for prey, though it was smaller at around 6 to 8&nbsp;meters (20-27&nbsp;feet) in length, 2.5&nbsp;meters (8&nbsp;feet) tall, and weighing 500&nbsp;kg up to 1&nbsp;tonne; it would have occupied a distinctly separate niche from its larger cousin which is estimated to have grown up to 12&nbsp;metres in length with the largest definitive specimen of 9&nbsp;metres. ''Ceratosaurus'' had a longer, more flexible body, with a deep tail shaped like that of a crocodilian.<ref name=CWG20/> This suggests that it was a better swimmer than the stiffer ''Allosaurus''. A recent study by 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.<ref></ref> 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.

==Classification==
thumb|250px|''Ceratosaurus nasicornis''
Relatives of ''Ceratosaurus'' include ''classification of ''Ceratosaurus'' and its immediate relatives has been under intense debate recently. ''Ceratosaurus'' is unique in its characters; it is too advanced and basal tetanuran-like to be a large, late coelophysoid; and too primitive in many manners to be a true carnosaur. Its closest relatives appear to be the abelisaurs from the Cretaceous, but again, ''Ceratosaurus'' is an enigma in its existing tens of millions of years before them with no obvious Early Cretaceous link between them. 
thumb|left|''Ceratosaurus'' skeleton from 1896, depicted in an erroneous upright position 
In the past, ''Ceratosaurus'', the Cretaceous abelisaurs, and the primitive coelophysoids were all grouped together and called Ceratosauria, defined as "theropods closer to ''Ceratosaurus'' than to Aves". Recent evidence, however, has shown large distinctions between the later, larger and more advanced ceratosaurs and earlier forms like ''Coelophysis''. While considered distant from birds among the theropods, ''Ceratosaurus'' and its kin were still very bird-like, and even had a more avian tarsus than ''Allosaurus''. As with all dinosaurs, the more fossils found of these animals, the better their evolution and relationships can be understood.

== In popular culture ==

thumb| reconstruction of ''Ceratosaurus nasicornis''.
''Ceratosaurus'' has appeared in several films, including the first live action film to feature dinosaurs, Fantasia'' (1940), ''Ceratosaurus'' are shown as opportunistic predators attacking ''Stegosaurus'' and ''The Land That Time Forgot'' (1975) where it battles a ''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). More recently, a ''Ceratosaurus'' makes 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, but is later killed and eaten by an ''Allosaurus''.