Some time ago I found a fantastic internet-site which shows how evolution could have worked, if natural history had taken other ways. There are hundreds (or thousands?) of animals which could have evolved from known extinct or modern species, many with great pictures. They also invented some very interesting hypothetical ways of squid and nautiloid evolution. Just have a look at it:
http://www.bowdoin.edu/~dbensen/Spec/Baleen-squid.htm
http://www.unet.univie.ac.at/~a0000265/Spec/Ammonoidea.html

That must have been fun! we could probably come up with some more, but the art work is great, as is the attention to detail. :notworth:

great stuff, makes you wonder "hey, why didn't that happen during evolution?"

One six-mile-wide asteroid might be a probable reason.