When, in the early 1990s, Josep Quintana found an animal bone on Minorca, a small Mediterranean island off the coast of Spain, he never imagined it belonged to a member of the biggest known rabbit species.
The discovery of the Nuralagus rex, which roughly translates to ‘Minorcan king of hares,’ was published this week in the Journal of Vertebrate Paleontology. Quintana, an independent researcher and leader of the study, joined forces with two paleontologists from the Institut Català de Paleontologia in Barcelona to try to pin down the characteristics of this unique species from bone remains.
The most distinct trait of this rabbit, which lived on the island 3 to 5 million years ago, is its extraordinarily big size. It weighted an average of 12kg, or about 10 times more than the common European rabbit.
That the mammal reached such a size could be a consequence of an evolutionary phenomenon known as ‘island gigantism.’ Put simply, animals isolated on islands grow to larger sizes than their mainland relatives. “Since small size usually makes it easier for herbivores to escape or hide from predators, the decreased predation pressure on islands can allow them to grow larger,” as neatly explained on Wikipedia.
The absence of predatory animals may have equally influenced other traits of the N. rex. In particular, it developed a “short and stiff vertebral column” because it didn’t have to hop to quickly escape predators. The giant rabbit was sluggish and “moved by low-gear walking instead of high-speed jumping,” according to the authors of the study.
More, compared to the size of its body, the animal had short ears and a “relative small size of sense-related areas of the skull,” including eye sockets. These characteristics suggest poor hearing and vision, other likely consequences of a stress-free lifestyle.
But it wasn’t all laziness for the N. rex. It knew how to forage for food on rocky Minorca. As suggested by the shape of its claws, the giant mammal frequently dug for roots and tubers, a behavior contrary to that of modern rabbits that excavate to build protective burrows rather than to search for food.
Despite the odd traits, the Minorcan animal has cranial and dental features typical of rabbits so, according to Brian Kraatz, quoted by National Geographic, there is “no question” it is a lagomorph (the scientific name given to rabbits, hares and pikas). Kraatz is a paleontologist at the Western University of Health Science in Pomona, California who did not take part in the study.
The reasons for the disappearance of the N. Rex are unknown. But given its clumsy walking and its inferior hearing and vision, it is not hard to imagine it wouldn’t survive if predators arrived in Minorca. Kraatz believes “he got too comfortable, and eventually went extinct.”