Evolutionist summoner and evolutions dependent on base form

[Level 20 NPC]

Hi, I'm building a summoner and I've read the evolutionist archetype.
At 8th level the summoner can change his eidolon's base form: i don't understand what would happen to evolutions only available to a specific base form, like pounce or trample, that the eidolon picked when he was another base form and could not pick after this change.
The eidolon still has them but cannot use them? It's forced to change these evolutions? Or the archetype actually makes possible to have a biped with pounce, an aquatic with constrict and so on?
Are there any FAQs anywhere? Thanks

[Melkiador]

If you lose the prerequisite for an ability, then you can’t use that ability.

But you can only change the base form when gaining a level, and you choose evolutions at the same time.

Quote:

Whenever the summoner gains a level, he must decide how these points are spent, and they are set until he gains another level of summoner.

So drop evolutions you don’t qualify for and choose evolutions you do qualify for.