Old Earth Ministries Online Dinosaur Curriculum

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Lesson 10 - Ceratosaurus

Ceratosaurus, meaning "horned lizard", in reference to the horn on its nose, was a large predatory dinosaur from the Late Jurassic Period (Kimmeridgian to Tithonian), found in the Morrison Formation of North America, in Tanzania and Portugal.

Ceratosaurus was a fairly typical theropod, with a large head, short forelimbs, robust hind legs, and a long tail.  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 (Sereno 1997) (i.e. similar to modern birds). A row of small osteoderms was present down the middle of the back.


Quick Facts


Length:  20-30 feet

Weight:  1,000 - 2,200 lbs

Date Range:  153-148 Ma, Kimmerridgian - Tithonian Age, Jurassic Period



Mounted Juvenile Ceratosaurus (Picture Source)


The skull of Ceratosaurus was quite large in proportion to the rest of its body.


Artist Impression (Picture Source)

 Each premaxilla contained only three teeth, and each maxilla (the main tooth-bearing bones in the upper jaw) held between twelve and fifteen flattened, exceptionally long teeth. Each dentary (the main tooth-bearing bone in the lower jaw) bore eleven to fifteen teeth. The prominent nose horn is formed from protuberances of the nasal bones. A juvenile specimen is known in which the two halves of the horn are not yet fused together. 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 enlargement of the lacrimal bones.

Postcranial skeleton

Uniquely among theropods, Ceratosaurus possessed dermal armor, in the form of small osteoderms running down the middle of its back. The tail of Ceratosaurus comprised about half of the body's total length. It was thin and flexible, with high vertebral spines.


Ceratosaurus scale

Scale Drawing of Ceratosaurus (Picture Source)

The type specimen was an individual about 17.5 feet (5.3 m) long; it is not clear whether this animal was fully grown. David B. Norman (1985) estimated that the maximum length of Ceratosaurus was 20 feet (6 m). A particularly large Ceratosaurus specimen from the Cleveland-Lloyd Quarry (UUVP 81), discovered in the mid-1960s, may have been up to 30 feet (8.8 m) long.

Marsh (1884) suggested that Ceratosaurus weighed about half as much as Allosaurus. In Predatory Dinosaurs of the World, published in 1988, Gregory S. Paul estimated that the C. nasicornis holotype skeleton came from an animal weighing about 524 kilograms (1,160 lb). A large femur from the Cleveland-Lloyd Quarry represents a much bigger and heavier individual, whose bulk was estimated by Paul at about 980 kilograms (2,200 lb). This specimen (UUVP 56) was later assigned by James H. Madsen and Samuel P. Welles to the new species C. dentisulcatus. A considerably lower figure was proposed by John Foster, a specialist on the Morrison Formation, in 2007. Foster used an equation provided by J.F. Anderson and colleagues to estimate mass from femur length, which yielded an approximate weight of 275 kilograms (606 lb) for C. magnicornis and 452 kilograms (996 lb) for C. dentisulcatus.

Discovery and species

Ceratosaurus is known from the Cleveland Lloyd Dinosaur Quarry in central Utah and the Dry Mesa Quarry in Colorado. The type species, described by O. C. Marsh in 1884 and redescribed by Gilmore in 1920, is Ceratosaurus nasicornis. Two further species were described in 2000: C. magnicornis (from the Fruita Paleontontological Area, outside Fruita, Colorado) and C. dentisulcatus. C. magnicornis has a slightly rounder horn but is otherwise highly similar to C. nasicornis; C. dentisulatus is larger (over 7 meters), slightly more derived, and has an unknown horn shape (assuming it had them).



Ceratosaurus nasicornis fossil, North American Museum of Ancient Life. (Picture Source)

Relatives of Ceratosaurus include Genyodectes, Elaphrosaurus, and the abelisaurs, such as Carnotaurus. The classification of Ceratosaurus and its immediate relatives has been under intense debate recently. Ceratosaurs are unique in their characters; they share some primitive traits with coelophysoids, but also share some derived traits with tetanuran theropods not found in coelophysians. 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.


Ceratosaurus lived alongside dinosaurs such as Allosaurus, Torvosaurus, Apatosaurus, Diplodocus, and Stegosaurus. 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.

Nasal horn

Ceratosaurus skull

(Picture Source)

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 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 Diplodocus trapped in mud. 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 very 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). 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. 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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Bay State Replicas - Ceratosaurus nasicornus maxilla ( portion of the upper jaw ), click on Teeth to view