An unusual dinosaur from the Late Cretaceous of Romania and the island rule

Abstract

Island faunas are natural laboratories of evolutionary change and have long fascinated biologists. The peculiar ecological conditions on islands have frequently led to the evolution of endemic taxa that differ dramatically in body size and/or morphology from their mainland relatives. Many large animals tend to become smaller on islands, and small ones generally become larger—a phenomenon known as the island rule (1, 2). Perhaps the best-known examples from the fossil record are the pony-sized elephants and pig-sized hippopotami that populated Crete and various other Mediterranean islands during the Pleistocene and Holocene (3). Other examples include the Miocene hedgehog Deinogalerix from Italy, which attained a body length of about 70 cm (4), and the prehistoric rat Coryphomys from East Timor, which may have tipped the scales at 6 kg (5). Insular gigantism has also been found in certain groups of birds such as owls (6).