Hi Hajar and Kevin,
This is just the opinion of a non-scientist with no significant knowledge of evolutionary biology, but.... how do we know that these forms aren't just deleterious mutations of existing ammonite species, rather than normal representatives of distinct species?
We see so many deleterious mutations of modern species -- animals with two heads, or extra limbs, or one eye, etc. -- and if some future paleontologist happened to find their fossilized remains, perhaps s/he too would mistake them for normal representatives of distinct species, or perhaps late-stage forms of a species headed for extinction.
I'm just wondering if there's a possibility that the same thing is going on here.
Just curious,
Tani
(not-too-well-informed laysquid)