text: carnotaurus carnotaurus / / is a genus of large theropod dinosaur that lived in south america during the late cretaceous period , between about 72 and 69 . 9 million years ago . the only species is carnotaurus sastrei . known from a single well - preserved skeleton , it is one of the best - understood theropods from the southern hemisphere . the skeleton , found in 1984 , was uncovered in the chubut province of argentina from rocks of the la colonia formation . derived from the latin [ ] ( " flesh " ) and taurus ( " bull " ) , the name carnotaurus means " meat - eating bull " , alluding to its bull - like horns . carnotaurus is a derived member of the abelisauridae , a group of large theropods that occupied the large predatorial niche in the southern of gondwana during the late cretaceous . the phylogenetic relations of carnotaurus are uncertain ; it may have been closer to either majungasaurus or aucasaurus . carnotaurus was a lightly built , bipedal predator , measuring 8 to 9 m ( 26 to 30 ft ) in length and weighing at least 1 . 35 metric tons ( 1 . 33 long tons ; 1 . 49 short tons ) . as a theropod , carnotaurus was highly specialized and distinctive . it had thick horns above the eyes , a feature unseen in all other carnivorous dinosaurs , and a very deep skull sitting on a muscular neck . carnotaurus was further characterized by small , vestigial forelimbs and long and slender hindlimbs . the skeleton is preserved with extensive skin impressions , showing a mosaic of small , non - overlapping scales measuring approximately 5 mm in diameter . the mosaic was interrupted by large bumps that lined the sides of the animal , and there are no hints of feathers . the distinctive horns and the muscular neck may have been used in fighting conspecifics . according to separate studies , rivaling individuals may have combated each other with quick head blows , by slow pushes with the upper sides of their skulls , or by ramming each other head - on , using their horns as shock absorbers . the feeding habits of carnotaurus remain unclear : some studies suggest the animal was able to hunt down very large prey such as sauropods , while other studies find it preyed mainly on relatively small animals . carnotaurus was well adapted for running and was possibly one of the fastest large theropods . description carnotaurus was a large but lightly built predator . the only known individual was about 8 – 9 metres ( 26 – 30 ft ) in length , making carnotaurus one of the largest abelisaurids . only ekrixinatosaurus and possibly abelisaurus may have been similar or larger in size , though the incomplete remains of these genera make size estimations imprecise . its mass is estimated to have been 1 , 350 kg ( 1 . 33 long tons ; 1 . 49 short tons ) 1 , 500 kg ( 1 . 5 long tons ; 1 . 7 short tons ) and 2 , 100 kg ( 2 . 1 long tons ; 2 . 3 short tons ) in separate studies that used different estimation methods . carnotaurus was a highly specialized theropod , as seen especially in characteristics of the skull , the vertebrae and the forelimbs . the pelvis and hindlimbs , on the other hand , remained relatively conservative , resembling those of the more basal ceratosaurus . both the pelvis and hindlimb bones were long and slender . the left thigh bone of the individual measures 103 cm in length , but shows an average diameter of only 11 cm . skull the skull , measuring 59 . 6 cm ( 23 . 5 in ) in length , was proportionally shorter and deeper than in any other large carnivorous dinosaur . the snout was moderately broad , not as tapering as seen in more basal theropods like ceratosaurus , and the jaws were curved upwards . as in other abelisaurids , the facial bones , especially the nasal bones , were sculptured with numerous small holes and spikes . in life , a wrinkled and possibly keratinous skin would have covered these bones . a prominent pair of horns protruded obliquely above the eyes . these horns , formed by the frontal bones , were thick , cone - shaped but in cross - section somewhat vertically flattened , and measured 15 cm ( 5 . 9 in ) in length . in life , they would probably have formed the bony cores of much longer keratinous horns . the proportionally small eyes were situated in the upper part of the keyhole shaped ( eye sockets ) . the upper part was slightly rotated forward , probably permitting some degree of binocular vision . the teeth were long and slender , as opposed to the usually very short teeth seen in other abelisaurids . on each side of the upper jaws there were four premaxillary and twelve maxillary teeth , while the lower jaws were equipped with fifteen dentary teeth per side . in contrast to the robust - looking skull , the lower jaw was shallow and weakly constructed , with the dentary ( the foremost jaw bone ) connected to the hindmost jaw bones by only two contact points . the lower jaw was found with hyoid bones , in the position they would be in if the animal was alive . these slender bones , supporting the tongue musculature and several other muscles , are rarely found in dinosaurs because they are not connected to other bones and therefore get lost easily . vertebrae the vertebral column consisted of ten cervical ( neck ) , twelve dorsal , six fused sacral and an unknown number of caudal ( tail ) vertebrae . the neck was nearly straight , rather than having the s - curve seen in other theropods , and also unusually wide , especially towards its base . the top of the neck 's spinal column featured a double row of enlarged , upwardly directed bony processes called epipophyses , creating a smooth trough on the top of the neck vertebrae . these processes were the highest points of the spine , towering above the unusually low spinous processes . the epipophyses probably provided attachment areas for a markedly strong neck musculature . a similar double row was also present in the tail , formed there by highly modified caudal ribs , in front view protruding upwards in a v - shape , their inner sides creating a smooth , flat , top surface of the front tail vertebrae . the end of each caudal rib was furnished with a forward projecting hook - shaped expansion that connected to the caudal rib of the preceding vertebra . the forelimbs were proportionally shorter than in any other large carnivorous dinosaurs , including tyrannosaurus . the forearm was only a quarter the size of the upper arm . there were no in the hand , so that the metacarpals articulated directly with the forearm . the hand showed four basic digits , though apparently only the middle two of these ended in finger bones , while the fourth consisted of a single splint - like metacarpal that may have represented an external ' spur ' . the fingers themselves were fused and immobile , and may have lacked claws . carnotaurus differed from all other abelisaurids in having proportionally shorter and more robust forelimbs , and in having the fourth , splint - like metacarpal as the longest bone in the hand . a 2009 study suggests that the arms were vestigial in abelisaurids , because nerve fibers responsible for stimulus transmission were reduced to an extent seen in today 's emus and kiwis , which also have vestigial forelimbs . skin carnotaurus was the first theropod dinosaur discovered with comprehensive fossil skin impressions . these impressions , found beneath the skeleton 's right side , come from different body parts , including the lower jaw , the front of the neck , the shoulder girdle , and the rib cage . the largest patch of skin corresponds to the anterior part of the tail . originally , the right side of the skull also was covered with large patches of skin — this was not recognized when the skull was prepared , and these patches were accidentally destroyed . still , the surface texture of much of the right side of the skull is very different from that of the left side , and probably shows some features of the scalation pattern of the head . the skin was built up of a mosaic of polygonal , non - overlapping scales measuring approximately 5 mm ( 0 . 20 in ) in diameter . this mosaic was divided by thin , parallel grooves . scalation was similar across different body parts with the exception of the head , which apparently showed a different , irregular pattern of scales . there is no evidence of feathers . uniquely for theropods , there were large knob - like bumps running along the sides of the neck , back and tail in irregular rows . each bump showed a low ridge and measured 4 to 5 cm ( 1 . 6 to 2 . 0 in ) in diameter . they were set 8 to 10 cm ( 3 . 1 to 3 . 9 in ) apart from each other and became larger towards the animal 's top . the bumps probably represent clusters of condensed scutes , similar to those seen on the soft frill running along the body midline in hadrosaurid ( " duck - billed " ) dinosaurs . stephen czerkas ( 1997 ) suggested that these structures may have protected the animal 's sides while fighting members of the same species ( conspecifics ) and other theropods , arguing that similar structures can be found on the neck of the modern iguana where they provide limited protection in combat . classification carnotaurus is one of the best - understood genera of the abelisauridae , a family of large theropods restricted to the ancient southern supercontinent gondwana . abelisaurids were the dominant predators in the late cretaceous of gondwana , replacing the carcharodontosaurids and occupying the ecological niche filled by the tyrannosaurids in the northern continents . several notable traits that evolved within this family , including shortening of the skull and arms as well as peculiarities in the cervical and caudal vertebrae , were more pronounced in carnotaurus than in any other abelisaurid . though relationships within the abelisauridae are debated , carnotaurus is consistently shown to be one of the most derived members of the family by cladistical analyses . its nearest relative may have been either aucasaurus or majungasaurus ; this ambiguity is largely due to the incompleteness of the aucasaurus skull material . a recent review suggests that carnotaurus was not closely related with either aucasaurus or majungasaurus , and instead proposed ilokelesia as its sister taxon . carnotaurus is eponymous for two subgroups of the abelisauridae : the carnotaurinae and the carnotaurini . paleontologists do not universally accept these groups . the carnotaurinae was defined to include all derived abelisaurids with the exclusion of abelisaurus , which is considered a basal member in most studies . however , a 2008 review suggested that abelisaurus was a derived abelisaurid instead . carnotaurini was proposed to name the clade formed by carnotaurus and aucasaurus ; only those paleontologists who consider aucasaurus as the nearest relative of carnotaurus use this group . discovery the only skeleton ( holotype macn - ch 894 ) was unearthed in 1984 by an expedition led by argentinian paleontologist josé bonaparte . this expedition also recovered the peculiar spiny sauropod amargasaurus . it was the eighth expedition within the project named " jurassic and cretaceous terrestrial vertebrates of south america " , which started in 1976 and which was sponsored by the national geographic society . the skeleton is well - preserved and articulated ( still connected together ) , with only the posterior two thirds of the tail , much of the lower leg , and the hind feet being destroyed by weathering . during fossilization , the skull and especially the muzzle were crushed laterally , while the premaxilla were pushed upwards onto the nasal bones . as a result , the upward curvature of the upper jaw is artificially exaggerated in the holotype . the skeleton belonged to an adult individual , as indicated by the fused sutures in the braincase . it was found lying on its right side , showing a typical death pose with the neck bent back over the torso . unusually , it is preserved with extensive skin impressions . in view of the significance of these impressions , a second expedition was started to reinvestigate the original excavation site , leading to the recovery of several additional skin patches . the skeleton was collected on a farm named " sastre " near moreno in the department of chubut province , argentina . because it was embedded in a large hematite concretion , a very hard kind of rock , preparation was complicated and progressed slowly . in 1985 , bonaparte published a note presenting carnotaurus sastrei as a new genus and species and briefly describing the skull and lower jaw . the generic name ( latin [ ] – " flesh " and taurus – " bull " ) refers to the bull - like horns , while the specific name sastrei honors angel sastre , the owner of the ranch where the skeleton was found . a comprehensive description of the whole skeleton followed in 1990 . after abelisaurus , carnotaurus was the second member of the family abelisauridae that was discovered . for years , it was by far the best - understood member of its family , and also the best - understood theropod from the southern hemisphere . it was not until the 21st century that similar well - preserved abelisaurids were described , including aucasaurus , majungasaurus and , allowing scientists to re - evaluate certain aspects of the anatomy of carnotaurus . the holotype skeleton is displayed in the argentine museum of natural sciences , bernardino rivadavia ; replicas can be seen in this and other museums around the world . sculptors stephen and sylvia czerkas manufactured a life - sized sculpture of carnotaurus that is now on display in the natural history museum of los angeles county . this sculpture , ordered by the museum during the mid - 1980s , is probably the first life restoration of a theropod showing accurate skin . age and paleoecology originally , the rocks in which carnotaurus was found were assigned to the upper part of the formation , which was considered to be approximately 100 million years old ( albian or cenomanian stage ) . later they were realized to pertain to the much younger la colonia formation , dating 72 to 69 . 9 million years ago ( late cretaceous , lower maastrichtian stage ) . thus , carnotaurus was the latest south american abelisaurid known . by the late cretaceous , south america was already isolated from both africa and north america . the la colonia formation is exposed over the southern slope of the north patagonian massif . most vertebrate fossils , including carnotaurus , come from the formation 's middle section ( called the middle facies association ) . this part likely represents the deposits of an environment of estuaries , tidal flats or coastal plains . the climate would have been seasonal with both dry and humid periods . the most common vertebrates collected include lungfish , turtles , crocodiles , plesiosaurs , dinosaurs , lizards , snakes and mammals . some of the snakes that have been found belong to the families and , such as . turtles are represented by at least five taxa , four from ( ) and one from ( ) . among the marine reptiles is the plesiosaur of the family . mammals are represented with , which was considered the first record of a south american , and argentodites coloniensis , possibly of multituberculata . in 2011 , the discovery of a new enantiornithine bird from the la colonia formation was announced . paleobiology function of the horns carnotaurus is the only known carnivorous bipedal animal with a pair of horns on the frontal bone . the use of these horns is not entirely clear ; several interpretations have revolved around use in fighting conspecifics , in display , or in killing prey . greg paul ( 1988 ) proposed that the horns were butting weapons and that the small would have minimized the possibility of hurting the eyes while fighting . gerardo mazzetta and colleagues ( 1998 ) suggested that carnotaurus used its horns in a way similar to rams . they calculated that the neck musculature was strong enough to absorb the force of two individuals colliding with their heads frontally at a speed of 5 . 7 m / s each . fernando novas ( 2009 ) interpreted several skeletal features as adaptations for delivering blows with the head . he suggested that the shortness of the skull might have made head movements quicker by reducing the moment of inertia , while the muscular neck would have allowed strong head blows . he also noted an enhanced rigidity and strength of the spinal column that may have evolved to withstand shocks conducted by the head and neck . other studies suggest that rivaling carnotaurus did not deliver rapid head blows , but pushed slowly against each other with the upper sides of their skulls . thus , the horns may have been a device for the distribution of compression forces without damage to the brain . this is supported by the flattened upper sides of the horns , the strongly fused bones of the top of the skull , and the inability of the skull to survive rapid head blows . gerardo mazzetta and colleagues ( 1998 ) propose that the horns might also have been used to injure or kill small prey . though horn cores are blunt , they may have had a similar form to modern bovid horns if there was a keratinous covering . however , this would be the only reported example of horns being used as hunting weapons in animals . jaw function and diet analysis of the jaw design of carnotaurus by mazzetta and colleagues ( 1998 , 2004 , 2009 ) suggests that the animal was capable of quick bites , but not strong ones . quick bites are more important than strong bites when capturing small prey , as shown by studies of modern - day crocodiles . furthermore , these researchers noted a high degree of flexibility ( ) within the skull and especially the lower jaw , somewhat similar to modern snakes . elasticity of the jaw would have allowed carnotaurus to swallow small prey items whole . in addition , the front part of the lower jaw was hinged , and thus able to move up and down . when pressed downwards , the teeth would have projected forward , allowing carnotaurus to spike small prey items ; when the teeth were curved upwards , the now backward projecting teeth would have hindered the caught prey from escaping . mazzetta and colleagues also found that the skull was able to withstand forces that appear when tugging on large prey items . carnotaurus may therefore have fed mainly on relatively small prey , but also was able to hunt large dinosaurs . this interpretation was questioned by françois therrien and colleagues ( 2005 ) , who found that the biting force of carnotaurus was twice as high as that of the american alligator , which may have the strongest bite of any living tetrapod . these researchers also noted analogies with modern komodo dragons : the flexural strength of the lower jaw decreases towards the tip linearly , indicating that the jaws were not suited for high precision catching of small prey but for delivering slashing wounds to weaken big prey . as a consequence , according to this study , carnotaurus must have mainly preyed upon large animals , possibly by ambush . robert bakker ( 1998 ) found that carnotaurus mainly fed upon very large prey , especially sauropods . as he noted , several adaptations of the skull — the short snout , the relatively small teeth and the strong back of the skull ( occiput ) — had independently evolved in allosaurus . these features suggest that the upper jaw was used like a serrated club to inflict wounds ; big sauropods would have been weakened by repeated attacks . locomotion mazzetta and colleagues ( 1998 , 1999 ) presumed that carnotaurus was a swift runner , arguing that the thigh bone was adapted to withstand high bending moments while running . the ability of an animal 's leg to withstand those forces limits its top speed . the running adaptations of carnotaurus would have been better than those of a human , although not nearly as good as those of an ostrich . scientists calculate that carnotaurus had a top speed of up to 48 – 56 km ( 30 – 35 mi ) per hour . in dinosaurs , the most important locomotor muscle was located in the tail . this muscle , called caudofemoralis , attaches to the fourth trochanter , a prominent ridge on the thigh bone , and pulls the thigh bone backwards when contracted . scott persons and phil currie ( 2011 ) note that in the tail vertebrae of carnotaurus the caudal ribs did not protrude horizontally ( " t - shaped " ) , but were angled against the vertical axis of the vertebrae , forming a " v " . this would have provided additional space for a caudofemoralis muscle larger than in any other theropod — the muscle mass was calculated at 111 to 137 kilograms ( 245 to 302 lb ) per leg . therefore , carnotaurus could have been one of the fastest large theropods . while the caudofemoralis muscle was enlarged , the muscles situated above the caudal ribs would have been proportionally smaller . these muscles , called the longissimus and muscle , were responsible for tail movement and stability . to maintain tail stability in spite of reduction of these muscles , the caudal ribs bear forward projecting processes interlocking the vertebrae with each other and with the pelvis , stiffening the tail . as a consequence , the ability to make tight turns would have been diminished , because the hip and tail had to be turned simultaneously , unlike in other theropods .