I actually went hunting around on the internet for information on this, and what I found was murky at best. While there is no reason to think that a dog can't have twin puppies, in a purebred dog in particular, how would you know? Puppies of most breeds look exactly alike when they are born. All dogs have fraternal twins. The mother dog releases multiple eggs that are each fertilized by a different sperm. But for the egg to be fertilized by 1 sperm, then divide and each half to form it's own puppy would be more rare, and honestly, somewhat unnecessary in an animal that naturally is prone to having litters of 4, 8, or even 12 puppies. Even so, dogs that appear to be identical when born they grow up and end up looking quite different as far as markings go. Let me link an example. http://www.ashgi.org/color/twins.htm As you can see despite the fact that these puppies looked identical when newborn as they got older, they ended up looking different with different markings. I guess in humans, even identical twins can grow up and look different from each other so that's not far fetched. I do know that likelihood of identical twins happening in some animals is almost unheard of in others. In horses for example, not only is twinning of any sort, fraternal or identical highly unusual, it's almost always a death sentence for the mare. I suspect that since there's a hereditary factor involved with twinning, few mares have actually survived to pass the 'twinning' gene to their offspring. Compare this with sheep. Sheep have multiple births (twins, triplets, and very rarely, quadruplets) about 15 percent of the time. That means basically 1 in every 7 sheep has multiple births. There are actually some sheep breeds that will have a multiple birth more than 50 percent of the time!! In fact, the more prolific breeds of sheep will actually have quadruplets about 1.5% of all births. That's fairly amazing, that means about 1 in 67 of this breed of sheep will have quadruplets. Compare this to human women. 1 in 85 women will have any kind of multiple birth (and that's on the rise because of modern fertility drugs). The chance of having triplets, quadruplets and other higher order births is extremely rare, the chance of that happening is less than 0.2%. That's a huge statistical difference. To summarize, I do think dogs have twins. But I think most of the time it's not even noticible.
Yes dogs can have twins. IMO that is. I had a friend breed a litter and two of the pups (one male one female) shared a placenta. These pups look identical in color and markings. The dogs have the same white markings in the same way, in the same place. We call em twins because to us sharing a placenta/egg makes them twins and they look identical. Even if they didn't look identical I would venture to say they were twins because of them coming out of the same sack.