Carnotaurus sastrei: The Short-Handed Sprinter

Article by: J. D. Dixon
Edited by: Adam Manning, Lewis Haller, Jack Wood
, and Harry T. Jones

Carnotaurus sastrei striding across the Cretaceous of Argentina, towering above Yaminuechelys sp., an extinct variety of turtle. Artwork by Henry Sharpe.

Name: Carnotaurus sastrei
Name Meaning: Meat-Eating Bull
Age: Late Cretaceous (Campanian-Maastrichtian)
Diet: Carnivore
Size: 9 metres in length approx.
Weight: 1500 kg approx.
Location: Argentina

Carnotaurus sastrei was first discovered in 1984, when a team of palaeontologists found a near-complete and fully articulated skeleton on an Argentinian farm. This was designated as holotype MACN-CH 894, and was fully described in 1990 by José Bonaparte, Fernando Novas, and Rodolfo Coria. The genus name, Carnotaurus, means ‘meat-eating bull’, while the species name, sastrei, honours the owner of the ranch where the fossil was found. The fossil was found in the La Colonia Formation, and its discovery helped establish Abelisauridae as a distinct family of dinosaurs. The same expedition that discovered Carnotaurus also yielded the sauropod Amargasaurus cazaui.

Carnotaurus was found to have skin impressions preserved along its right side, one of the first theropod dinosaurs to exhibit such preservation. The skin was scaly, and so showed that this dinosaur was a non-feathered theropod, unlike animals such as Velociraptor. The majority of these scales were small, but some osteoderms (thicker scales) were found along the back and tail. These may have acted as an armour, providing protection during combat.

The skull had undergone some degree of deformation but was still well-preserved, showing the animal had a short head with a compressed snout. Its eyes faced forwards, meaning Carnotaurus probably had stereoscopic vision and could easily perceive depth. This dinosaur also had a rather peculiar feature, reduced forelimbs. When thinking of short arms, Tyrannosaurus rex is often the butt of the joke, but Carnotaurus really shows how small things could get. Carnotaurus’ lower arm was approximately a quarter of the length of its upper arm, and was tipped with four stubby digits. The entire arm was tiny, and the part of the spine which supplied the nerve fibres to the arms was so reduced that the arm likely hung uselessly from the torso. This suggests the arm was vestigial, meaning it was a functionless remnant of a structure seen in the dinosaur’s ancestors.

A 3D render of Carnotaurus sastrei by Jacob Baardse. Note the majority of the body is covered in small scales, while thicker osteoderms can be seen along the neck, back, and tail.

Carnotaurus is perhaps most easily identified by the two horns located above its eyes. Interestingly, this species is actually the only example of a bipedal carnivorous dinosaur with horns over the eyes, and there are two main theories regarding their use. The first theory states that the horns would have been used in combat, similar to modern rams. It has been found that the muscles of Carnotaurus could have functioned as shock-absorbers, meaning if two adults ran into each other headfirst, their musculature could have handled such a blow. The second theory is hunting. It is thought that the horns may have had a keratin coating, making them longer in the animal’s life than those of the fossil preserved. This hypothesis states that the horns could have been used to injure or kill small animals, and if it is correct, it would be the only occurrence of the use of horns to kill prey.

The femur and tail muscles of Carnotaurus indicate that the species was capable of fast running, even short bursts of sprinting. However, some of their tail bones interlocked very closely, which probably caused a diminished ability to make tight turns when moving with speed. Analyses of the skull suggest this dinosaur was capable of a fast bite rather than a powerful one, at a relatively low 3,341 Newtons. This all indicates that this predator likely went after small animals. Carnotaurus appeared in the southern hemisphere after the disappearance of carcharodontosaurids, much larger theropod predators. It is hypothesised that while these apex beasts hunted the massive titanosaurs in the area, Carnotaurus later evolved to pick off smaller, more agile prey.

The discovery of Carnotaurus sastrei was key in understanding the abelisaurid group, and finds like this greatly aid the field of palaeontology. It may be a unique dinosaur with some rather strange features, like useless arms and contested horns, but this prehistoric bull was definitely a force to be reckoned with.

Image References

[1] Carnotaurus sastrei striding across the Cretaceous of Argentina, towering above Yaminuechelys sp., an extinct variety of turtle. Artwork by Henry Sharpe.
[2] A 3D render of Carnotaurus sastrei by Jacob Baardse.

Information References and Further Sources
[1] Bonaparte, J. F., Novas, F. E., and Coria, R. A. (1990). ‘Carnotaurus sastrei Bonaparte, The Horned, Lightly Built Carnosaur from the Middle Cretaceous of Patagonia’, Natural History Museum of Los Angeles County Contributions in Science, 416. Accessed 3rd September 2020. Click Here.
[2] Carter, N. (Unknown). ‘The Weird Dinosaurs Saga: Carnotaurus’, Blogosaur: Philip J. Currie Dinosaur Museum. Accessed 6th September 2020. Click Here.
[3] Cerroni, M. A., Canale, J. I., and Novas, F. E. (2020). ‘The skull of Carnotaurus sastrei Bonaparte 1985 revisited: insights from craniofacial bones, palate, and lower jaw’, Historic Biology, pp. 1-42. Accessed 3rd September 2020. Click Here.
[4] Dorling Kindersley. (2009). ‘Cretaceous: Vertebrates’, in Prehistoric. Great Britain: Dorling Kindersley Limited. pp. 321.
[5] Mazzetta, G. V., Cisilino, A. P., Blanco, R. E., and Calvo, N. (2009). ‘Cranial mechanics and functional interpretation of the horned carnivorous dinosaur Carnotaurus sastrei’, Journal of Vertebrate Paleontology, 29 (3), pp. 822-830. Accessed 3rd September 2020. Click Here.
[6] Mazzetta, G. V., Fariña, R. A., and Vizcaíno, S. F. (1998). ‘On the Palaeobiology of the South American Horned Theropod Carnotaurus sastrei Bonaparte’, Gaia, 15, pp. 185-192. Accessed 29th August 2020. Click Here.
[7] Méndez, A. H. (2012). ‘The cervical vertebrae of the Late Cretaceous abelisaurid dinosaur Carnotaurus sastrei, Acta Palaeontologica Polonica, 59 (3), pp. 569–579. Accessed 3rd September 2020. Click Here.
[8] Persons IV, W. S., and Currie, P. J. (2011). ‘Dinosaur Speed Demon: The Caudal Musculature of Carnotaurus sastrei and Implications for the Evolution of South American Abelisaurids’, PLOS ONE, 6 (10): e25763. Accessed 29th August 2020. Click Here.
[9] Ruiz, J., Torices, A., Serrano, H., and López, V. (2011). ‘The Hand Structure of Carnotaurus sastrei (Theropoda, Abelisauridae): Implications For Hand Diversity and Evolution in Abelisaurids’, Palaeontology, 54 (6), pp. 1271-1277. Accessed 3rd September 2020. Click Here.
[10] Senter, P. (2010). ‘Vestigial skeletal structures in dinosaurs’, Journal of Zoology, 280 (1), pp. 60-71. Accessed 3rd September 2020. Click Here.
[11] Tykoski, R. S., and Rowe, T. (2004). ‘Ceratosauria’, in Weishampel, D. B., Dodson, P., and Osmólska, H (2nd ed.) The Dinosauria. University of California Press. pp. 47-70.
[12] Yong, E. (2011). ‘Butch tail made Carnotaurus a champion dinosaur sprinter’, National Geographic. Accessed 3rd September 2020. Click Here.