How about [the Italian wall lizards](https://en.wikipedia.org/wiki/Italian_wall_lizard) that [evolved new muscles around their intestines](http://news.nationalgeographic.com/news/2008/04/080421-lizard-evolution_2.html) after being introduced to an island? ([other article](http://scienceblogs.com/pharyngula/2008/04/23/still-just-a-lizard/), [actual paper](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2290806/))