In casual speech what does ja na mean?
As in this example:
Googling for it only turns up results for じゃない。
Like @himself noted, it does mean
葉人をつかまえたんだな. While some dialects do have this change, more importantly it's used to characterise the speaker as a stereotypical wise old male (usually in anime or otherwise in a fiction).
じゃ = だ in some dialects. So this is probably 葉人をつかまえたんだな.
I believe the
Is a localized way to say
んだ which in turn is an everyday speech abbreviation of the actual form of
のだ where the
の carries an explanatory tone of the sentence based on context (i.e. the person is explaining something based on a query from a previous sentence) and the
だ represents the positive state of being and in this case is a less formal way of saying
Feel free to correct me if I'm wrong.