Nopcsa studied Transylvanian dinosaurs intensively, even though they were smaller than their "cousins" elsewhere in the world. For example, he unearthed six-meter-long sauropods, a group of dinosaurs which elsewhere commonly grew to 30 meters or more, which he named "Magyarosaurus". Nopcsa deduced that the area where the remains were found was an island, Hațeg Island (now the Haţeg or Hatzeg basin in Romania) during the Mesozoic era. He theorized that "limited resources" found on islands commonly have an effect of "reducing the size of animals" over the generations, producing a localized form of dwarfism. Nopcsa's theory of insular dwarfism—also known as the island rule—is today widely accepted. Additional pygmy sauropods, named "Europasaurus", were recently discovered in northern Germany.