In Ancestor, Baby McButter is the genetically-engineered creature that rips its way out of the womb and belly of the cow dubbed Molly McButter, and like the creatures gestated in the other cows is a quadrupedal, fur-covered carnivore, with long claws and massive mouth containing large, sharp teeth.
Baby McButter is one of two Ancestors which are individually named and described in the novel. McButter is characterized by an all-white head with a black patch surrounding one eye. It is said that this distinctive characteristic mirrors a similar coloring on the face of her cow mother, Molly McButter. Baby McButter is also missing an ear which was the result of an encounter with Sven Ballantine's dog, Mookie, shortly after Baby McButter was born.
Baby McButter and her Ancestor brood seem to have a very high metabolism, were frequently motivated by hunger, and required a significant amount of energy to hunt.
Baby McButter is the result of the fetus that was implanted in the Genada lab cow named Molly McButter. She is decidedly the Alpha female of the Ancestors seemingly more intelligent and tactical thinking than her brethren. She seems to be more intelligent than average Ancestors creature and heads their never ending search for food. In the end, even after her fellow Ancestors drowned in the freezing water of Lake Superior, Baby McButter stood her ground and faced death with an open mouth.