Hi - I don't know what the format for reporting bugs is here, so I'm just going to go for it. I apologize if I missed the formatting post somewhere.
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System: Mac with OSx Sierra 10.12.6
Niche Build: 0.9.2
Island: Tiny Green
Description: Upon reaching adulthood tamed Bearyena became a normal adult untamed Bearyena.
Note: It's possible that this happens when the tamed Bearyena is female? But I couldn't find anything on it with the exception of other players reporting the bug.