Syndactyly is the medical term for webbed or conjoined fingers or toes. In most cases the fingers are connected only by skin. It is rare that the bones are also fused together.
Dodo birds became extinct because of the combination of overhunting by humans and non-native predators that were introduced by humans to their native island. Dodo birds only inhabited the island of Mauritius, where they had no natural predators. Accordingly, the dodo bird had lost the power of flight and possessed few defensive behaviors by the time humans arrived on the island.
Habitat loss and modification are probably to blame for the extinction of these two butterflies. The Western Black Rhinoceros (Diceros bicornis longipes) was declared extinct in 2011 but for some reason it received a lot of press in late 2013. Here is a comprehensive breakdown of how we lost this magnificent beast.