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Why Do Nine-Banded Armadillos Give Birth to Quadruplets Every Time?

Armadillos are placental mammals under the order Cingulata. They are known for the bony plates that cover their entire body which serve as their first line of defense against predators. While there are different subspecies of this mammal, the nine-banded armadillo has a unique birthing pattern. Why do they give birth by 4s?

Nine-banded armadillos consistently give birth to quadruplets. This is because a single egg splits into four identical embryos after getting fertilized.

What is an Armadillo?

Armadillos are yellowish-brown animals with strongly curved claws and basic peglike teeth that lack enamel. They also come in a variety of sizes. In the United States, the most common subspecies is the nine-banded armadillo which is about 76 cm long. 

They are armored animals found mainly in the tropical and subtropical regions of Central and South America. Most of the 20 species can be found in open areas such as meadows, but several can also be found in woodlands. In most armadillos, the carapace is a collection of plates covering much of the body, including the head, legs, and tail. Except for one species, the carapace is almost hairless.

The carapace is made up of bony transverse bars covered in skin-derived solid scales. The number of movable bands in their armor gives the three-, six-, and nine-banded armadillos their names. The nine-banded armadillo is the only species found in the United States.

Since its discovery in Texas in the 1800s, its distribution has expanded into numerous southern states. In some areas, eight-banded individuals of this species are prevalent. The pichi or Zaedyus pichiy, a frequent resident of Argentine Patagonia, and the bigger hairy armadillo the Chaetophractus villosus, which goes far into southern Chile. (Source: Britannica

More on the Nine-banded Armadillo or Dasypus novemcinctus 

The Dasypus novemcinctus is the only vertebrate that consistently produces identical quadruplets. When a female’s egg is fertilized, it divides into four genetically identical embryos that share one placenta. It’s unclear how and why this unusual pattern developed and continues to exist.

We normally think of genetic diversity as a benefit for creatures that have numerous births.

The nine-banded armadillo, however, defies this by creating clones.

Aside from generating milk for her young, the nine-banded armadillo mother is not particularly attentive, and the male is much less so. However, supplying adequate nutrients for her young to develop and prosper may be her most important responsibility.

Extra nutrients, especially calcium and phosphate, are required to build a bony carapace. Although ossification of the osteoderms begins in the womb, you can imagine that having a thin and flexible carapace, that is, one that is not entirely formed, makes the birth of four babies no less easy. Fortunately, the majority of the carapace’s development occurs after birth.

The armadillo mother does this primarily through a calcium-deficient insectivorous diet. Armadillos also have a slower metabolic rate than most animals. Despite these apparent disadvantages, babies born at 100 grams grow swiftly and can forage on their own by two months. 

The ability of the armadillo mother to do all of this for her four identical offspring is as baffling as the fact that she has four identical babies. (Source: Carnegie Museum of Natural History)

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