Only two cases of Siamese white-tailed deer (Odocoileus virginianus) had previously been reported in the scientific literature. Thanks to a mushroom picker, one more has just been studied and not just any: the first known case of fawns Odocoileus virginianus whose gestation has been completed. These animals were found in southeastern Minnesota in May 2016. The corpse was clean and dry: the Siamese fawns had died at most 4 days before.
Two hearts, one pericardial sac
As a result of this discovery, the harvester called the State Department of Natural Resources. Researchers were able to freeze the specimen to keep it in shape until they could do the autopsy. They also gave these animals a CT scan and an MRI scan. As reported in the April 2018 issue of The American Midland Naturalist, these animals had joined bodies but distinct necks and heads.
According to the imaging techniques, the skull as well as the cervical vertebrae, several ribs and most of the thoracic vertebrae were duplicated. Similarly, the researchers observed two distinct intestinal tracts. One complete, from the esophagus to the anus and the other composed of discontinuous segments. The liver was divided and malformed and biologists noted the presence of “two separate hearts sharing a single pericardial sac”. Placed in the water, the lungs sank “indicating that the fawns are stillborn” continues the study: they have never been filled with air.
“The doe tried to take care of them after giving birth”
“Their anatomy indicates that these fawns have never been viable,” Gino D’Angelo, co-author of the study, said in a statement, “yet they were found to be clean and in a natural position which suggests that the doe has tried to take care of them after childbirth. The maternal instinct is something very strong,” marvels the researcher.
For the moment, no explanation is privileged to explain the birth of these Siamese. “Even for humans we do not know,” says D’Angelo, “we think this is due to an abnormal division of cells during the early stages of embryo development.” But the precise mechanisms that govern this process are yet to be elucidated.