Imagine being the paleontologist who finds a single fossil skull and from that one clue reconstructs an entire dinosaur. Abelisaurus comahuensis, “Abel’s lizard,” is known to science from just such a find.
In 1985 José F. Bonaparte and Fernando E. Novas announced the discovery of this South American carnosaur in a Spanish language scholarly journal, Ameghiniana. A carnosaur is a Cretaceous therapod (meat-eating dinosaur walking on two legs); Abelisaurus was so unlike other carnosaurs that Bonaparte and Novas proposed an entirely new family, Abelisauridae.
The partial skull—much of its right side is missing—was found in the lower part of the Allen Formation, early Maastrichtian geologic layer of the Lago Pellegrini stone quarries, Department of General Rocas, Province of Río Negro, Argentina.
Abelisaurus is named in honor of the director of the Museo de Cipolleti, Professor Roberto Abel, the man responsible for unearthing the actual fossil skull from diggings in Patagonia, a rugged and remote region of Argentina.
The process of finding and naming a new dinosaur requires many hands; Prof. Abel discovered the skull, while Bonaparte and Novas “diagnosed,” or categorized and classified, Abelisaurus through exhaustive examination of the skull. The name they proposed pays tribute to Abel while acknowledging the geographic rarity of a South American carnivorous dinosaur: comahuensis refers to the Comahue region, where the skull was discovered. South American carnivorous dinosaurs are not common, though the prey dinosaurs they dined on, such as sauropods, are found in abundance.
This carnivorous, ground-dwelling dinosaur, a theropod, probably roamed South America and Africa some 74 million to 70 million years ago in the Early Campanian period of the Late Cretaceous. It probably moved on its rear legs, using its smaller front legs much as Tyrannosaurs did.
Between seven and nine meters in length and around two meters tall, tipping the scales at just over 1,360 kilograms (around a ton and a half), Abelisaurus had a head nearly a meter long—the extant skull is 85 centimeters. It had a narrow head with many short, knife-like teeth. Paleontologists base some of this physiology on other abelisaurids, such as Aucasaurus and Majungasaurus.
Studying the incomplete skull to unlock every secret of the animal, Bonaparte and Novas realized that the high, narrow skull had many openings, lightening the dinosaur’s head and allowing for rapid movement—the sort of sudden thrusting and swinging needed in a predatory dinosaur. It shared similarities to Tyrannosaurus, though Abelisaurus may not have been able to use its tiny front legs as easily as Tyrannosaurus did.
Abelisaurus comahuensis is classified in taxonomy as Animalia, Chordata, Reptilia, Saurischia, Theropoda, Carnosauria, Abelisauridae, Abelisaurinae. This graceful shorthand may seem daunting to understand at first, but each part tells any paleontologist important information about the extinct creature. Animalia, the kingdom, shows that the dinosaur was an animal (as opposed to a plant or protist). The phylum and class designations, Chordata and Reptilia, show this dinosaur had a brain and hollow nerve chord—a spinal cord—and was a reptile. The order, suborder and infraorder (Saurischia, Theropoda, Carnosauria) indicate lizard-like hips on a bipedal carnivore. The family, the last stop before designating an individual species, is Abelisauridae.