Implications of Marsupial Births for an Understanding of Behavioural Development

Abstract

A review of birthing in marsupials shows that there are at least three distinct methods. In the opos- sums (Didelphidae), possums, and kangaroos (Phalangeroidea), the expelled newborns crawl from the urogenital sinus to the pouch. In the bandicoots (Peramelidae), the expelled newborn remain attached to the placenta via the umbilical cord while they swim from the urogenital sinus to the pouch. In the carnivorous Dasyuridae, the newborn are expelled in a column of viscous fluid in which they “swim up” to the tunnel between the urogenital sinus and the pouch and then move to the pouch. Some of the recent anatomical studies, on the relative development of the neural system in newborn marsupials and on the behaviours of the newborns within the three birthing methods, have reawakened interest in the mechanisms that might be used to find the pouch. The motor patterns occurring in the newborn marsupials have many similarities to the motor patterns that appear in eutherian embryos at these same developmental stages. Studies that correlate the motor behaviours with the sensory and neural development of newborn marsupials could have important benefits for the understanding of the early organization of behaviour in mammals in general.