The question of whether a joey is born without hind legs stems from the extreme prematurity of marsupial birth. The simple answer is no; all four limbs are present. However, the hind legs are so incredibly underdeveloped that they are often mistaken for being completely absent. This newborn marsupial, such as a kangaroo or wallaby, is born in a highly embryonic state, requiring an immediate physical feat to survive.
The Embryonic State at Birth
A joey is born after an exceptionally short gestation period, often 28 to 36 days for a kangaroo. It emerges at a stage comparable to a seven-week-old human embryo. This newborn is astonishingly small, typically measuring only about one inch long and weighing less than a gram. It is pink, hairless, and blind, resembling a fetus more than a fully formed animal.
The newborn’s physical state is defined by a striking asymmetry in limb development. The forelimbs are comparatively robust, muscular, and equipped with small, functional claws. These well-developed forelimbs contrast sharply with the hind limbs, which are merely rudimentary buds or tiny stumps, non-functional for movement. The tail is also undeveloped, reinforcing the appearance of an unfinished creature. This disproportionate development of the forelimbs is the physical mechanism that makes the joey’s survival possible.
The Journey to the Pouch
The newborn joey’s first task is an arduous, solitary journey known as the “great climb.” Immediately after emerging from the birth canal, the tiny creature must navigate the mother’s fur to reach the safety of the pouch, or marsupium. This climb is powered entirely by the joey’s instinct and its disproportionately large, clawed forelimbs, which it uses to pull itself upward.
The mother prepares the path by licking a track in her fur from the birth canal up to the pouch entrance, but she does not physically assist the joey. This lick-track provides a clear, moisture-laden path that the joey follows using its innate sense of direction. The non-functional hind legs and tail are dragged behind the joey during this three- to five-minute vertical ascent. Once inside the pouch, the joey latches onto a teat, which swells in its mouth to ensure continuous attachment for feeding.
Post-Natal Development and Metamorphosis
The journey into the pouch marks the transition from brief internal gestation to prolonged external development. The pouch provides a stable environment for the joey to complete its growth. Once attached to the teat, the joey remains largely immobile for several months, continuously feeding on specialized milk.
During this time, the joey undergoes a dramatic metamorphosis, primarily involving the rapid growth of the hindquarters. The small, rudimentary hind legs and tail begin to catch up to the rest of the body, growing much larger and stronger than the forelimbs. Fur begins to develop around three months, and the eyes and ears open as the nervous system matures. The joey typically starts to poke its head out around six months of age. It will not leave the pouch permanently until its hind legs are powerful enough to support its weight and facilitate hopping locomotion, a process that can take eight to eleven months in larger species.
The Marsupial Reproductive Strategy
The joey’s highly underdeveloped state at birth is a consequence of the unique marsupial reproductive strategy, which differs fundamentally from that of placental mammals. Marsupials have a simple, non-invasive placenta or a yolk-sac-based nourishment system that cannot sustain the embryo for a long period inside the uterus. This limitation forces the young to be born extremely prematurely.
The remainder of fetal development is transferred to the external pouch. This strategy is an evolutionary adaptation allowing the mother to invest less energy in a long, internal pregnancy. By shifting the bulk of development to the pouch, the mother maintains a reproductive flexibility that is highly advantageous in unpredictable environments.