Scientists recently discovered the first known case of identical dog twins named Cullen and Romulus. As published by Cari Romm in Science of Us and reported by the BBC, the twins were discovered during a Cesarean section delivery by veterinarian Kurt De Cramer in South Africa.

The average dog will give birth to five or six puppies per litter. That is the norm. What is unusual in the case of Cullen and Romulus is the fact they shared a single placenta. That they survived is even more remarkable as puppies that share a placenta ordinarily do not live long outside the womb. This is due to complications that arise relative to a single placenta attempting to provide twice the normal amount of nutrients and oxygen required of two dogs as opposed to just one. This event adds dogs to the small list of animals able to birth identical twins that also includes humans and nine-banded armadillos which in the case of the later, give birth to identical quadruplets, each with their own placenta.

De Cramer and his colleagues confirmed the identical status of Cullen and Romulus through DNA testing after their birth and published their finding in the journal Reproduction in Domestic Animals. The fact that Cullen and Romulus are the first documented case of identical twin dogs does not mean there have not been others. Scientists were fortunate enough in this case to acquire genetic confirmation.