That has Dutch framing style written all over it. A Dutch (house) frame has bents that are closely spaced, generally 3-4'. The tie beams are the only floor joists, that is there are no joists running between the bents. Certain 2x T&G decking (generally SYP and DF) can span between the bents. This is the standard frame workshop taught by Jack Sobon and Dave Carlon and Hancock Shaker Village.

I agree with Jim on the mortise. Maybe even 1.25".