Meanings of implausibly large in English

We come to a portcullis-like door and she pauses, fumbling with an implausibly large key ring.

Penny's character wore a fluffy pink bikini that barely covered what even Owen would admit were implausibly large breasts.

Implausibly large in arid mountainous terrain, the family of lobelia plants remarkably predate the formation of tall mountains in eastern Africa, to which they've adapted.