You can't get big dogs from small dogs. All dogs came from 2 giant-sized dogs. One theory is that the animals on Noah's ark were babes.

Of course not all animal species or genuses were on the ark. Not any sea creatures, not any birds although they were resting atop the ark, but only 7 pairs of clean animals and a pair of unclean animals according to God's will as he sent them. All the different land animals came from common ancestor species and degraded and changed genus over time.

Again, all dogs come from 2 dogs on Noah's ark. The bible lists dogs as unclean so there were only 2. Wolves are the biggest dogs so all dogs come from 2 wolfs.