Kangaroos do not lay eggs. As mammals, they give birth to live young. They are marsupials, characterized by a unique reproductive strategy: a very short gestation period followed by extensive development within a specialized pouch. This differs significantly from egg-laying animals and most other mammals.
Kangaroo Reproduction: A Marsupial’s Journey
Kangaroos, like all marsupials, exhibit a distinct reproductive process. Following fertilization, gestation is remarkably brief, typically 28 to 35 days. The newborn kangaroo, called a joey, is born in an extremely underdeveloped state: tiny, often resembling a jelly bean or a lima bean, hairless, blind, and with underdeveloped hind limbs.
Despite its immature appearance, the joey possesses strong forelimbs and an innate sense of direction. Immediately after birth, it instinctively crawls through the mother’s fur to reach her abdominal pouch, the marsupium. Once inside, the joey attaches to a nipple, which swells to secure it. This ensures a continuous supply of milk for its growth and development within the pouch for several months.
The joey remains in the pouch, nursing and growing, for six to eight months or more. During this time, its eyes open, fur grows, and limbs develop. Even after venturing out, it frequently returns for nourishment and protection until fully weaned and independent, which can be up to a year or longer. Female kangaroos can also exhibit embryonic diapause, where a fertilized egg’s development is temporarily halted, allowing multiple offspring at different developmental stages: one in the pouch, another outside, and a dormant embryo.
Beyond Kangaroos: Animals That Lay Eggs
While kangaroos do not lay eggs, many other animal groups reproduce this way. Birds lay eggs that hatch outside the mother’s body. Reptiles, such as snakes, lizards, and turtles, also lay eggs, often with leathery shells. Fish and amphibians typically lay their eggs in water; fish eggs are often fertilized externally, and amphibian eggs lack hard shells. Insects also reproduce by laying eggs.
Within the mammal class, only monotremes lay eggs. These include the platypus and four species of echidnas, found in Australia and New Guinea. Unlike other mammals, monotremes possess a single opening for waste and reproduction, called a cloaca, similar to birds and reptiles. They lay leathery-shelled eggs and produce milk to nourish their young after hatching, though through pores on their skin rather than nipples.