A Bull-Horned Carnivore's Hide
In 1984, paleontologist José Bonaparte led an expedition into Argentina's Chubut Province that uncovered a singular fossil. On a farm named "Pocho Sastre," the team found a nearly complete and articulated skeleton of a large predatory dinosaur. The fossil was so remarkable that it became the only known specimen of its kind: Carnotaurus sastrei, a name that means "Sastre's meat-eating bull." The name references both the ranch owner, Angel Sastre, and the dinosaur's most prominent feature: two thick, 15 cm (5.9 in) horns protruding from above its eyes.
What made this discovery exceptional were the extensive skin impressions found preserved along the skeleton's right side. While skin from the skull was accidentally destroyed during preparation, patches from the jaw, neck, shoulder, and tail remained. This fossil provides the most complete look at the skin of any large theropod. The skin was a mosaic of small, non-overlapping polygonal scales, each about 5 millimeters in diameter. Studding this scaly hide were larger, conical bumps, or "feature scales," measuring 4 to 5 cm in diameter. These were distributed randomly across the animal's body and lacked any bony core. The discovery confirmed that at least one lineage of large theropods was completely scaly, showing no evidence of feathers.
An Anatomy of Extremes
Carnotaurus was a predator of unusual proportions that lived between 72 and 69.9 million years ago. It measured 7.5 to 8 meters (24.6 to 26.2 ft) in length and weighed between 1.3 to 2.1 metric tons. Its skull, at 59.6 cm long, was short and deep, and its jaws were curved upwards. The forward-facing orientation of its eyes suggests it had some degree of binocular vision, a useful trait for a predator. The function of its solid bone horns is still debated; theories range from species recognition and display to direct use in combat with rivals, much like modern rams.
Perhaps even more peculiar than its horns were its forelimbs. The arms of Carnotaurus are considered vestigial, meaning they were functionless remnants from its ancestors. They were proportionally smaller than those of Tyrannosaurus rex, with a lower arm that was only a quarter the length of the upper arm. The hands had four stubby, fused fingers that lacked claws and were likely immobile. Unlike its tiny arms, Carnotaurus possessed powerful hind legs and a muscular tail, anatomical features suggesting it was a fast runner capable of chasing down agile prey. Its skeleton was found in the La Colonia Formation, which preserves a record of a coastal plains or lagoon environment from the Late Cretaceous.