Marsupials

Pouched mammals (kangaroos, koalas, opossums) that diverged from placental mammals ~160 million years ago. The chapter uses marsupials to illustrate both convergence and its limits. Marsupials show remarkable convergence with placentals (marsupial mole vs. golden mole, thylacine vs. wolf, sugar glider vs. flying squirrel), but developmental constraints (young must climb to pouch at birth) prevented evolution of whale-like flippers or bat-like wings.