http://www.aquaticcommunity.com/bett...ilfinforms.php
I ran across this while looking for some information in the Search Box on the Web. It is an article that really gives comprehensive information about the different fin types of the bettas and even says something about the new Feathered bettas that we spoke of that Teddy Bear is. (Dave and Stacy's little guy)
It seems that it is a type of offshoot of the Rosetail but a very desirable one. It is developed to help with the problem Rosetails have of their fins collapsing. I do know that this is a problem due to the massive weight that the fins seem to develop compared with the fish's body mass and the ability of the fish to manuever through the water with the finnage.
Rose