That you'd be way wrong. You are talking about a stretch in bone morphology as big as the span between Eohippus and horse. Paleological zoologists, who assign species names, don't usually know doodly about what critters could have mated with what. They are just guessing, and from recent results from anthropology, probably guessing way off the mark on the conservative side about this.
That's one of the amusing things about this micro-macro fossil gap argument. It is an argument about perfectly arbitrary designations with no real gritty reality behind them. It is just academic bookkeepping. Nobody knows what could mate with what, and bone morphology designations could be (when we can check it out, almost always, in fact, are) way, way off kilter from species separation.
If dogs were extinct, would creationists be running around hooting about the Great Dane/Chihuaua gap? You bet your butt they would.
So do you believe the brontosaurus actually existed?