Diminutive Dino

In 1895, Franz Baron Nopcsa examined a set of small sauropod dinosaur bones and concluded that they belonged to a species subjected to island dwarfism, and named it Magyarosaurus dacus. Island dwarfism (phyletic nanism) is the reduction in size of large animals that occurs when a species' gene pool is limited to a very small environment, such as an island, and the particular conditions in that environment (competition, food sources, territory, etc.). M. dacus was a titanosaurian sauropod from the Upper Cretaceous (Maastrichtian) and was about the size of a horse, which is very small when compared to other sauropod species. Since then, with the discovery of other large sauropods at the same site, it has come into question whether or not M. dacus was actually a dwarf or not.

More recently, these bones were examined for their microstructure, particularly the rebuilding that happens to bones as an animal ages. This analysis indicated that M. dacus had bone microstructure identical to that of a fully mature sauropod. The diminutive dino also had an extremely reduced growth rate but maintained the high metabolic rates typical of other sauropod species. Based on this research, they were able to show, conclusively, that M. dacus was indeed an island dwarf species. The other sauropod bones at the site were also shown to belong to a different sauropod species.

Here's the article:
Stein, K. et al. (2010) Small body size and extreme cortical bone remodeling indicate phyletic dwarfism in Magyarosaurus dacus (Sauropoda: Titanosauria). Proceedings of the National Academy of Sciences: published online. (DOI: 10.1073/pnas.1000781107)
and http://www.sciencedaily.com/releases/2010/05/100503111513.htm