You think you are confused. I've been working on the evolution of stomatopods for decades and the picture of how the raptorial appendages evolved is even more confused than when I started. This is partly because of the advent of molecular techniques to infer phylogeny and an improved fossil record. When I first proposed the two functional types of stomatopods - spearers and smashers - We knew that the earliest protostomatopods split off from other crustaceans about 400 million years ago. These animals clearly had five pairs of maxilipeds that were all about the same size and each ending in a hook. The first stomatopods with an enlarged raptorial appendage (2cd maxilliped) didn't appear for 200 million years later. By 100 million years ago, all of the major groups of modern stomatopods were present. The assumption was that spearers evolved first and since the major group that was mostly spearers was the Squilloids, we considered them as ancestoral to the Gonodactyloidea that contains the most smashers. However, with the inclusion of fossil groups in attempts to bulid a phylogeny, this did not seem to be the case. The gonodactyloids and lysiosquilloids seem to be more basal. (However, we have some preliminary molecular data that may reverse this again. Also, recent analysis of some early fossils show that the raptorial appendage was evolving as early as 360 million years ago. The first raptorial appendages probably had just a spike or blade, not a barbed spearing appendage or an inflated dactyl heel that was used as a hammer. The modern Hemisquilla dactyl is similar to these early appedages.
Smashing and spearing appears to have evolved at least a few times in different lines, so it is probably wrong to think that spearers evolved from smashers or or reverse.
Roy
