The hippopotamus that died last Tuesday in the Wildlands zoo in Emmen had the characteristics of a female on the outside, but the characteristics of a male on the inside. According to the animal park, this biological phenomenon has never been established with hippos.

The female hippopotamus Hasana died very suddenly last Tuesday, and the zoo wanted to know what the cause of death was. Hasana was transferred to the University of Utrecht, where she discovered that the animal had the characteristics of a female on the outside - with a vulva and the typical build - but had no womb on the inside. Instead, the vets discovered testicles and an organ that looks like a penis.

The zoo gives as possible explanation that Hasana was half a twin at birth. The brother has only lived for four days, but time together in the womb can, according to Wildlands veterinarian Job Stumpel, lead to the male elements in Hasana.

Contact in the womb

"With cows this is more common and there they are called heifers, a female calf, a kween," says Stumpel. "The membranes of the fetuses in the abdomen then make contact during development, whereby the female - in this case Hasana - is exposed to the male hormones of the sibling. As a result, the female animal develops male characteristics."

This phenomenon only occurs with cows, with humans and other animals it is very rare. With hippos it has never been seen before, the zoo says in a statement.

By the way, Hasana did not die from this biological phenomenon, an acute intestinal rotation turned out to be the cause of her sudden death.

Hippos are in prison on average fifty years old. Females are fully grown after five to six years and have matured after seven to fifteen years.