Although the fawns were found dead, according to a study published in the journal American Midland Naturalist, they had been groomed and in a natural position, suggesting that the doe tried to care for them after delivery.
A CT scan of the conjoined fawns shows completely separate heads and necks.
"It's amazing and extremely rare. We can't even estimate the rarity of this. Of the tens of millions of fawns born annually in the US, there are probably abnormalities happening in the wild we don't even know about," said D'Angelo.
A full examination of the conjoined twin fawns was a unique opportunity for researchers to study such a rare wildlife deformity, he said.
The hunter called the Minnesota Department of Natural Resources, where D'Angelo was working at the time. The fawns were frozen until a necropsy could be performed, so the specimen was kept in excellent condition, D'Angelo said.
They found that the fawns - which were does - had two separate necks and heads, but they shared a body. They had normal fur, normal heads and legs, and even 'almost perfect' spot patterns running up their necks, D'Angelo said.
Lab tests of the lungs confirmed the fawns never breathed air and were delivered stillborn, and the necropsy found that the does had a malformed, shared liver, extra spleens and gastrointestinal tracts, as well as two hearts that shared a single pericardial sac.
"Their anatomy indicates the fawns would never have been viable. Yet, they were found groomed and in a natural position, suggesting that the doe tried to care for them after delivery. The maternal instinct is very strong," D'Angelo said.
Conjoined twins are not unheard of in animals or humans, although most do not survive after birth. They are more commonly found in domestic animals - particularly in cattle and sheep - but far less common in wildlife.
Only two cases of conjoined twins have been found in white-tailed deer, but both were foetuses who had not yet been delivered.
Healthy twin fawns are the rule rather than the exception, because most adult does give birth to twins, D'Angelo said. Why these twins became conjoined is a mystery.
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