How would a scientist study the relationship between the frogamander and modern frogs and salamanders?

A Gerobatrachus hottoni (frogmander) a 290 million year old fossil has been found in Texas, the fossil which shows both frog and salamander traits has changed scientists opinions on the ancestry of amphibians. Scientists would now study the four distinct groups of leposondyls, temnospondyl, caecilians and amphibians.