Doctors at the Albert Sabin Children's Hospital in Fortaleza, Brazil, were shocked when a baby was born with a 12-centimeter "true tail" – one of around just 40 cases ever discovered.
The doctors decided to surgically remove the long human tail, which was equipped with a strange four-centimeter-thick ball of skin at the end.
The child's birth and the surgical removal of his tail were described in a case published in the peer-reviewed periodical the Journal of Pediatric Surgery Case Reports back in 2021.
How was a human baby born with a tail?
As stated in the case, all humans have tails while in the womb. It grows around four weeks after conception, but by the eighth week, it usually gets absorbed back into the body and becomes the coccyx. It only ever continues to grow as a tail in very rare cases.
But what makes this specific tail so unique is that it didn't contain any bone or cartilage. Rather, it was a "true tail."
The case noted that the first documented case of a "true tail" in humans was back in the 19th century.
The baby itself was reportedly born in the 35th week of pregnancy to a healthy mother in an otherwise normal pregnancy.
There were no complications in the baby's birth, other than the presence of a 12-centimeter tail – something that prenatal tests never detected.
An ultrasound later helped doctors confirm that the tail wasn't connected to the baby's nervous system, meaning they could safely operate to remove it.
Whether the parents requested the tail's removal or if the baby experienced any pain from it is unknown.
But what about the ball at the end of the tail?
After the surgery, doctors were able to determine that the tail was made of fetal fat and fibrous tissue, while the tail itself was made of just boneless tissue.
The tail itself is reportedly a "rare congenital anomaly" – one that scientists still can't explain.
As primates who evolved from monkeys, humans technically used to have tails. However, it is believed that this appendage was lost to humanity some 25 million years ago over the course of evolution. Some experts have theorized that losing the tail allowed the primates that would eventually become humans to have improved upright mobility.