Kurt de Cramer, a veterinarian  at Rant en Dal Animal Hospital in Mogale City, South Africa, made an anomalous discovery, reported by the BBC two weeks ago.
De Cramer was performing a cesarean section on an Irish wolfhound with prelabor distress and unusual uterine bulging. He operated on the mother’s uterus to extract what he thought to be excess fluid surrounding a fetus. That’s when he encountered the rare phenomenon of two fetuses sharing one placenta: identical twin puppies. Following the twins’ birth, de Cramer delivered their five siblings.
When the litter was two weeks old, de Cramer took the twins’ blood samples for DNA analysis by reproductive specialists Carolynne Joone of James Cook University in Townsville, Australia, and Johan Nöthling of the University of Pretoria in South Africa. Genetic profiling verified that Cullen and Romulus are identical, making them the first confirmed instance of monozygotic twinning in a dog.
While multiples are common across species, the only previous cases of identical offspring have been confirmed in humans and nine-banded armadillos, which left the researchers initially skeptical. "The twins looked very similar," Joone told the BBC. "But pups from the same litter often do. There were small differences in the white markings on their paws, chests and the tips of their tails. I wasn't sure they were monozygotic at all."
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Identical twin puppies?

Posted by The Animal Medical Center on Thursday, September 8, 2016
But the same gene can differ in its expression, hence the nonidentical features in the genetically identical Irish wolfhounds. "Human identical twins also have the same genes, but because those genes are expressed differently in each person, they have different freckle and fingerprint patterns," de Cramer told the BBC.

Identical twin dogs have never been seen before.

Posted by BBC Earth on Saturday, September 10, 2016
Cullen and Romulus continue to thrive. Despite being slightly smaller at birth, the twins had caught up to their littermates by the six-week weigh-in. There’s no doubt about it. These South African pups are twinning and winning.