When did they evolve from round to square?
This is from 1784.
Round is easy to make as a 3 oz ball is flattened according to “The Complete Dictionary of Arts and Sciences” from 1766.
Manner of making Sea-Bisket. The flour is first wet in the kneading-trough, with a sufficient quantity of water, and covered for some time with a cloth. It is then well kneaded with a brake, and the dough divided into pieces of about three ounces each. These pieces are again kneaded singly, and laid in rows, and the baker, after shaking some flour over them, lays another row upon the former; and continues kneading and placing his pieces of dough upon the last pieces, till the whole batch, or quantity baked at once, is finished: the pieces of dough are then flatted into cakes, pricked with an instrument for that purpose, and placed regularly in the oven, where they stand about half an hour, when they are taken out of the oven, and carried to the store-room. The pricking could have been made with a docker as shown
It all changed in the Industrial Revolution when Samuel Critcherson invented a machine and it was advertised in The Massachusetts Register and United States Calendar for the Year of Our Lord 1852 
It went from round balls that were flattened to large sheets of dough that were cut into squares and pricked with a large cutter.
