image: A tammar wallaby joey stays close to its mother as it explores its enclosure at the Smithsonian's National Zoo on May 30, 2008. Tammar wallabies are marsupials -- like kangaroos -- and after birth, offspring climb into their mothers' pouch where they nurse and continue developing over several months. The National Zoo has six wallabies -- two males, three females, and the joey whose sex is still unknown. Not wanting to disturb the delicate bond between the mother and baby, keepers have yet to separate them for an exam to determine the sex and weight. view more
Credit: Mehgan Murphy/Smithsonian's National Zoo