Mention sauropods, and most of us conjure images of giants. It's one of the classic dinosaur laws. But the fact is, they weren't all enormous. Case in point: cow-sized* Magyarosaurus dacus.
When flamboyant Transylvanian paleontologist Baron Franz Nopcsa first described the little sauropod at the end of the nineteenth century, he put forward the idea that it represented a case of insular dwarfism: when large species are confined to islands, which naturally possess a limited number of resources, they tend to get smaller over time. M. dacus wasn't the only example either; during the late Cretaceous, Europe was broken up into a bunch of islands. The Cretaceous rock of the Haţeg region where Nopcsa worked represents one of these islands and has produced a number of similarly "miniaturized" dinosaurs. Nopcsa's idea wasn't universally accepted though, and many claimed that his fossils represented juveniles.
While further discoveries have brought Nopcsa's hypothesis into the mainstream, it has now been pretty much validated by an international team of researchers led by Bonn University's Koen Stein and P. Martin Sander and Johns Hopkins' David Weishampel. By examining the microscopic structure of Magyarosaurus bones and comparing them to those of known adult sauropods, the team found that the little Transylvanian sauropods were, indeed, full grown. It's only one of several examples of island dwarfism among the dinosaurs, including the other denizens of "Haţeg Island." Recent work includes Sander's similar study of a Jurassic island sauropod, Europasaurus holgeri and last year's description of a new hadrosaur from Italy called Tethyshadros insularis.
On a side note, the story of Magyarosaurus dacus illustrates how political concerns sometimes influence the workings of science. When Nopcsa named his little sauropod, he initially called it Titanosaurus dacus. The name was changed to its current form by rival German paleontologist Freidrich von Huene after the Balkan wars to include the Hungarians in the fun; the Magyars are a Hungarian ethnic group (dacus refers to the historical name for Romania). I'm sure that this decision wasn't come to lightly by von Huene. He probably had hordes of angry Hungarians demanding it, pitchforks at the ready. I can't blame them.
More: Palaeoblog, Discovery.
* I hope at least one person initially misread that as crow-sized. That would be adorable.