For hundreds of years, people have been finding the remains of dinosaurs and other prehistoric creatures in Romania's Haţeg basin. The Cretaceous-age deposits are remnants of prehistoric islands that sported their own unique faunas, but in the days before fossils were recognized as being the remains of once-living animals, many considered them to be the bones of giants that the Bible said lived before Noah's flood. It was not until 1897 that paleontologists Gyula Halaváts and Franz Nopcsa rediscovered the dinosaur bones and realized what they were—but there was something very peculiar about the dinosaurs from these deposits.
As recognized by Nopcsa in the beginning of the 20th century, the dinosaurs of the 70-million-year-old Haţeg strata seemed to be descendants of dinosaurs which had evolved much earlier, but they were considerably smaller than their relatives elsewhere. The hadrosaur Telmatosaurus and the sauropod Magyarosaurus, were especially tiny, and Nopcsa proposed that this was because of what biologists call the "island rule." Although the mechanism by which it might work is still being investigated, paleontologists and field biologists have noticed that when large animals become isolated on islands they often become dwarfed over time, sometimes leading to the formation of entirely new species. (The so-called "hobbit," Homo floresiensis, appears to be an example of this phenomenon from our own lineage.)
Despite Nopcsa's hypothesis about the Haţeg dinosaurs, relatively little had been done to test his ideas, and so paleontologists Michael Benton, Zoltan Csiki, Dan Grigorescu, Ragna Redelstorff, Martin Sander, Koen Stein and David Weishampel reexamined the geology and paleontology of the site. They found that during the late Cretaceous, there was an island about 80,000 square kilometers that contained the Haţeg site, and this island was itself part of a collection of islands which existed in what is now central Europe. More importantly, an examination of the microstructure of the dinosaur bones, which can be used to determine the age and growth pattern of dinosaurs, showed that both Telmatosaurus (at about 5 meters long) and Magyarosaurus (at about 6 meters long) were fully grown adults with a small body size—they truly were dwarfed dinosaurs.
This "island rule" did not apply to all the dinosaurs on Haţeg island, however. Some species are comparable in size to their counterparts elsewhere, meaning that dwarfing is not a rule for all species that became trapped on the island. The reason for this difference, as well as the trigger that caused Telmatosaurus and Magyarosaurus to become so small, is as yet unknown, but from the research carried out so far it appears that Nopcsa was right.
Benton, M., Csiki, Z., Grigorescu, D., Redelstorff, R., Sander, P., Stein, K., & Weishampel, D. (2010). Dinosaurs and the island rule: The dwarfed dinosaurs from Haţeg Island Palaeogeography, Palaeoclimatology, Palaeoecology DOI: 10.1016/j.palaeo.2010.01.026
Grigorescu, D. (2010). The Latest Cretaceous fauna with dinosaurs and mammals from the Haţeg Basin — A historical overview Palaeogeography, Palaeoclimatology, Palaeoecology DOI: 10.1016/j.palaeo.2010.01.030