Gerbatrachus hottoni is said to be the common ancestor of frogs and salamanders before they evolved separately. The fossils that were discovered of this species were found in 1995 but were not studied until 2008. Nicholas Hotton discovered the fossil but died two years later and was unable to finish studying the fossil. Jason Anderson and his team heard about the fossil at the Smithsonian and jumped on the opportunity to study it.
The fossil has a body plan similar to that of a salamander but has traits such as a short, mostly boneless tail. Also, he says "It's got a great big froggie ear and it's reduced the number of vertebrae in its back … but like salamanders, it shares a particular fusion of some ankle bones"(CBC news). Since this species has traits of both frogs and salamander Anderson like to call it a "Frogamander".
This species was walking the earth 50 million years before the dinosaurs and also predate the earliest frog and salamander fossils which did not occur until the dinosaur times as well. It was most likely living a large amount of its life in the water but was also able to move onto land similar to modern frogs. Given this information from the G. hottoni fossil, this species was most likely the common ancestor of both frogs and salamanders.
Also, you can listen to the frogamander segment from the Quirks and Quarks website
Nature paper: doi:10.1038/nature06865
CBC news article: http://www.cbc.ca/technology/story/2008/05/22/science-frog-salamander.html
Quirks and Quarks:http: //www.cbc.ca/quirks/episode/2008/05/24/birth-of-a-supernova-frogamander---a-missing-link-digging-deep-for-life-crafty-chameleon-camouflage/