South African veterinarian Kurt De Cramer was performing what he thought was a routine cesarean section on an Irish wolfhound when he came across something rather odd. He noticed the dog had an unusual bulge near the base of her uterus.
De Cramer made an incision and carefully extracted a puppy. Shocked, he immediately noticed a second puppy attached to the same placenta. He delivered five more healthy, live puppies, but he was fascinated by the first two. In hundreds of deliveries and 26 years of practice, this was the first time De Cramer had delivered two puppies from one placenta.
"When I realized that the puppies were of the same gender and that they had very similar markings, I also immediately suspected that they might be identical twins having originated from the splitting of an embryo," De Cramer told the BBC.
He collected blood samples from the two pups when they were 2 weeks old, then at six weeks took DNA samples by swabbing the insides of their cheeks. He also profiled the twins' siblings and called in a team of genetic experts to confirm his early suspicions. The tests and further study confirmed that the dog had given birth to the first known instance of monozygotic (identical) twin puppies. The team released the findings in the journal Reproduction in Domestic Animals.
Although this is the first recorded case in scientific literature, it's difficult to know how rare this really is. Most female dogs, also called bitches, often have several puppies in each litter and those pups can sometimes look very similar. Because DNA tests are rarely performed, there may have been other cases of twins that have just never been recorded.
"We are so lucky that this bitch ended up having a C-section," study co-author Carolynne Joone of James Cook University in Townsville, Australia, told the BBC. Otherwise, it's unlikely anyone would have noticed the similarity between the puppies.
"Yes, there would have been one less placenta than there were pups, but as the bitch often eats the placentas, the owner probably would have simply shrugged this off."
Cases of monozygotic twins have been reported in other species, but are extremely rare and most animals die before birth, according to the study's authors. The exceptions appear to be humans, of course, and the nine-banded armadillo, which gives birth to identical quadruplets.
"There have been rumors about twins in dogs before," says Joone. "We just happened to be lucky enough to be able to confirm it genetically."
The twin puppies were slightly smaller than their littermates at birth, but had reached similar size by the time they were about 6 weeks old. Named Cullen and Romulus, the pups are healthy and utterly unaware that they've made history.