“The ability to reproduce together and produce fertile offspring is actually what defines animals as belonging to the same species.”
That actually is not true. For example, domestic cats have interbred and produced fully fertile offspring with other cat species not even from the same genus that don’t look much like domestic cats such as the Asian Leopard Cat that has very different markings, or the Serval which is twice the size of a domestic cat and looks even less like one. Similarly, polar bears and grizzly bears have interbred and produced fertile offspring. The definition of “species” is somewhat arbitrary and cannot be appled to halachic questions.