All humans have a belly button, also called a navel. This is the point where the umbilical cord, once connected to the placenta while in your mother’s womb and served to transport oxygen and other nutrients between the fetus and the mother. After birth, the umbilical cord is no longer needed, so it is cut off and the opening heals up to form the belly button.

In the animal kingdom, belly buttons often form in the same way. Most mammals give live birth and also have a placenta and umbilical cord. In those cases, rather than having the umbilical cord cut off, it is often chewed off by the mother. This is often just before mom eats the placenta, which is rich in nutrients and can help to provide her the strength needed to recover after giving birth and to make enough milk for her new babies.

Most people would assume that the list of animals that have belly buttons would end there, but that is not actually the case. The dictionary definition of a belly button is as follows:

“A depression in the middle of the abdomen that marks the point of former attachment of the umbilical cord or yolk stalk.”

The important part here is the part that says ‘or yolk stalk.’ A yolk stalk is what connects an embryo to the yolk sac for nutrients. This can be found in marsupials, oviparous animals that are hatched from eggs, and viviparous reptiles and fish.

So, based on that definition, you will find a belly button on a huge range of animals, including humans, cats, snakes, some fish, kangaroos, and many more. The appearance of the belly button is different in each species, and on some of them, you can hardly tell that it is there at all. For animals like cats and dogs, the belly button is hidden under their fur, so it is easy to forget that it exists.

Since most animals need a way to get nutrients while they are still developing, they will typically have a placenta or a yolk sac, and therefore will have a belly button.

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