Which level of biological classification is the lowest level that butterflies (invertebrates) and dogs (vertebrates) have in common?

Butterflies and dogs are both animals, so they share the kingdom Animalia. They also share the broader domain Eukarya, but kingdom is a more specific classification level. They do not belong to the same family or species, so the lowest level they have in common is kingdom, choice kingdom.

AI-written and checked against the verified answer.