@JimmyJ,
When the fossil intermediate (fish and amphibian) was found in 2003 by hubin nd Deschler, it was thought that the "fisshopod" had developed these large front hand-like limbs that enabled it to haul itself out onto land as their swamps began drying out or seasonally declining (some of the fossils show it to have been about 7 to 9 feet long)EVERYONE thought that, Tiktallik displayed a lungfish style of large fore limbs with tiny little rear limbs that only began developing as the species hauled out more and more.
A new series of complete Tiktallik fossils have been found in the 375 million year old rocks of Elsmere island . What they show is that Tiktallik was a "hopeful monster" wherein its rear legs were already developed as functioning "finny feet' that allowed the fish to bound around the lake or stream bottom and the critter was already pretty much "pre-evolved" to have been motile on the land although it would have a few generations before its body would no longer have a "land dragging belly".
So, in this case, the animal had already undergone a significant change in its fin structures so they could act like swim fins AND, sort of proto feet that enabled the fish to bounce along the bottom.
As its always been discovered, evolution occurs in steps and always involves a new use for an old structure or limb.
Tiktallik hs become one of the most vocal examples of the "Hopeful Monster" (A body that has pre-evolved to accomplish something entirely different than it became ultimately associated with.
Neat!
