Our bodies carry a small, often overlooked mark: the belly button. This common feature is a scar, a remnant of a temporary connection that was once a lifeline. It prompts curiosity about whether other creatures in the animal kingdom share this anatomical detail.
Understanding the Human Navel
The human navel, or umbilicus, is a scar formed where the umbilical cord once connected a developing fetus to its mother’s placenta. This cord serves as a vital conduit during gestation, transporting oxygen and essential nutrients from the maternal bloodstream to the fetus. Simultaneously, it carries waste products, such as carbon dioxide and urea, away from the developing baby.
After birth, medical professionals typically clamp and cut the umbilical cord. The remaining stump dries and eventually falls off, leaving behind the characteristic indentation or protrusion known as the navel. The specific appearance of a human navel, whether an “innie” or an “outie,” is a normal variation determined by how the area heals.
Belly Buttons in Placental Mammals
All placental mammals possess a navel because their embryonic development relies on a placenta and an umbilical cord for nourishment and waste exchange within the mother’s womb. This broad category includes animals such as dogs, cats, cows, horses, whales, and bats. These animals also bear this mark of their prenatal connection.
While these animals have belly buttons, they are often far less noticeable than in humans. Their navels typically appear as small, flat scars, which can be difficult to locate, especially when covered by fur or hidden within skin folds. In many species, the mother will chew through the umbilical cord after birth, contributing to a less prominent scar compared to the cleanly cut and clamped human cord. This natural process results in minimal scarring that often blends seamlessly with their anatomy.
Animals Without a Navel
Animals that do not develop with a placenta and umbilical cord connection lack a navel. This includes a diverse range of creatures with different reproductive strategies. Monotremes, a unique group of mammals consisting of the platypus and echidnas, reproduce by laying eggs. Since their young develop outside the mother’s body within an egg, there is no need for an umbilical cord, and thus no resulting scar.
Marsupials, such as kangaroos, koalas, and opossums, represent another group without a distinct belly button. Their young are born at a very early, underdeveloped stage, often nourished initially by a yolk sac inside the womb for a brief period. After this short gestation, the tiny, embryo-like offspring migrate to the mother’s pouch, where they attach to a nipple and continue their development. While some marsupials may have a temporary, less developed placental connection, it does not leave a permanent scar equivalent to a navel.
Furthermore, all oviparous animals, which lay eggs, do not have belly buttons. This category encompasses a vast number of species, including birds, reptiles, amphibians, and most fish. Their embryos develop entirely within the egg, sustained by a yolk sac rather than an umbilical cord connection to the mother.