At university, a long time ago, I was told that evolution is about populations, hybridisation is about single specimens. That means that when you find, for example, weird ammonites with hybrid features, either you are lucky enough to have found the exact specimen that has been generated through cross-breeding (very unlikely) or you've come across a different species (most probable), whose features would be transmitted to the offspring; these features would respond to some external evolution-driving factor, such as different environment, large scale tectonic phenomena, etc. In any case, according to me, neither hybridisation nor evolution could be accounted for the abnormal, differentiated and asymmetrical growth of spines or other ornamentation on each side of the ammonite, that would definitely have problems in surviving, let alone transmit its new features to its offspring. One of the main distinctive features of ammonites is their symmetrical planispiral growth, and shells with asymmetrical ornamentation would be doomed to very quick extinction.
That means, making a long story short, that it is most probably pathology or damage that causes the strange growth.
On the other hand, it may happen that abnormal growths can result in making one specimen resemble some other species or genus, but I think that it does happen by chance, and that it could be the result of evolution - I think they called it "convergent evolution" when two different species, or genera, or even families or phyla, evolved into very similar forms - they gave us the example of a Brachiopod being exactly identical in shape to a Bivalve, can't remember the name, though.