Exhibit Spotlight: Carnotaurus sastrei
With Carnotaurus featuring so prominently in the recent Jurassic World: Fallen Kingdom trailer, it seems apropos to review the science on this genuinely bizarre dinosaur. Buckle up: this one’s gonna get weird.
Most people’s first impressions of Carnotaurus react to its bizarre, horn-capped, pug-nosed mug. Those horns represent a unique feature among known carnivorous animals—most horned animals eat plants, and the few horned carnivores either walk on four legs or, like Carnotaurus’ cousin Ceratosaurus, their horns grow too short or too thin for any kind of combat. Carnotaurus’ horns, however, had a robust enough design to serve as weapons. Structural reinforcement in the braincase and neck, coupled with unusually powerful neck muscles, suggest they may have used them for wrestling rituals with other Carnotaurus.
The function of its squashed snout remains a point of debate among scientists. Not only was it short and deep, but several skull bones connected only loosely. To deepen the mystery, the tooth-bearing bone of its lower jaw connected with the rear part at only two small places—a joint that may have served as a hinge. This may mean the animal’s cranium could expand to swallow whole prey or chunks of meat larger than its head. Some scientists suggest it worked its jaws outward somewhat like a shark to impale smaller prey; then, as the mouth closed, the teeth would draw the prey into its throat. Different studies disagree on its jaw strength, however. Some conclude it could take quick but weak bites for catching small prey (though many such predators tend toward longer jaws for a better chance of capture). Others have determined a much higher bite force for its short snout, and that its quick bite was meant to wound larger animals.
If you think T. rex had wimpy little arms, take another look at Carnotaurus. While T.rex had functional claws powered by huge muscles, the arm of Carnotaurus had reduced to complete uselessness. Only two of its four stubby, immobile fingers had claws, and it lacked wrist bones entirely. Its forearm only accounted for a quarter of the total length.
Scientists have only found one Carnotaurus skeleton, but it remained in such good condition that, like Amargasaurus, we consider it a well-known dinosaur. The skeleton only lacked the last 2/3 of the tail and the lower legs. In fact, it was so well-preserved that it even included the first-known skin impressions from a carnivorous dinosaur. These impressions showed large, bumpy scales running in irregular rows from the head to the base of the tail, with no trace of feathers. This means that, other than quibbles like a couple of extra hand claws or arm posture, our Carnotaurus sculpture may rank as the most accurate depiction in the park.
The base of its tail had some unusual features. In most dinosaurs the fins on the top of the tailbones cross like a “t” when viewed from the rear. Carnotaurus tail bones (the ones nearest the hips, at least) looked more like a “W.” This allowed more room for muscles that powered the legs forward, but it also reduced room for muscles that kept the tail stable. As a result, the shape of the bones shifted to stiffen the base of the tail. This made Carnotaurus a kind of dinosaurian dragster: it had awesome acceleration but couldn’t make tight turns at high speed.
Bottom line: all the features that make Carnotaurus so weird probably mean that it did one thing very well. Unfortunately, until we find more evidence, we can’t know what exactly that one thing was. Even so, Carnotaurus has taught scientists some pretty important things about dinosaurs, and remains an important find.
Novas, F. E., & Coria, R. A. (1990). Carnotaurus sastrei Bonaparte, the Horned, Lightly Built Carnosaur from the Middle Cretaceous of Patagonia. Contributions in Science. Natural History Museum of Los Angeles County, 416, 1-42.
Mazzetta, G. V., Cisilino, A. P., Blanco, R. E., & Calvo, N. (2009). Cranial Mechanics and Functional Interpretation of the Horned Carnivorous Dinosaur Carnotaurus sastrei. Journal of Vertebrate Paleontology, 29(3), 822-830.
Ruiz, J., Torices, A., Serrano, H., & López, V. (2011). The Hand Structure of Carnotaurus sastrei (Theropoda, Abelisauridae): Implications for Hand Diversity and Evolution in Abelisaurids. Palaeontology, 54(6), 1271-1277.
Persons IV, W. S., & 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.