One of facts about dogs is that they have many breeds...introduced by selective breeding by humans over the course of their relationship. At least, before Jeff's use of the Chronovac. After all, in the timeline that was being written, dogs had been domesticating humans for thousands of years, breeding them for attributes they preferred. And dogs themselves, while they did have races, were much less varied.
As Andrew and Julia turned into playmates, Mason's attention had gone elsewhere, to a nearby bowl of some unknown meat. He walked over to it and began to gobble it up, face first.
Taylor, his mother, followed him. "That yours?" She asked, already starting to lose vocabulary.
"Mine," he agreed. His midsection grew, as did his arms and legs...they were suddenly the same size. He was becoming a rather large, by new standards, human. He paused his eating, licking his face with a increasingly long tongue full of drool. He turned to Taylor, revealing wild facial hair that had suddenly grown on his cheeks and growled a bit.