 The adipose fin , which is present in over 6 @,@ 000 teleost species , is often thought to have evolved once in the lineage and to have been lost multiple times due to its limited function . However , a 2014 study challenges this idea and suggests that the adipose fin is an example of convergent evolution . In <unk> , the adipose fin develops from an outgrowth after the reduction of the larval fin fold , while in <unk> , the fin appears to be a remnant of the fold . 
