improved natual attack.

[cryosphinx]

does the feat improved natural attack stack wiht the eidolon evolution improved damage?

[General Chaos]

It does not, (un)fortunately. Stacks with size bonuses to dice though.

[Drejk]

Why would they not stack? They are different abilities. Were there any official rulling that they do not stack?

[Rellen]

Unless there is errata I am unaware of they stack fine.