Oops, did i say that?

A. Monotremes - primitive mammals represented by the duck-billed platypus (so unusual that museum personnel in London believed that the first specimen they received from Australia was a fake) and the echidna; females have mammary glands with external pores but no nipples; oviparous (like reptiles).
B. Marsupials - young born very altricial; reared in a pouch called a marsupium; originated in Australia and South America before Australia became isolated (no placental mammals are native to Australia; all introduced by settlers; all niches were filled, however compare the now extinct marsupial wolf to the N. American timber wolf - this illustrates the evolutionary theory of convergence: animal species in different geographic but similar areas "converge" on an optimal body type for those habitats; other examples: dolphins, sharks and ichthyosaurs (extinct) in the oceans).

1. Many marsupial species in South America are believed to have become extinct the last time the Central American land bridge (isthmus) formed; placental mammals from N. America migrated southward and out-competed, preyed upon, gave diseases to the marsupials living there. The only exception is the opossum which has successfully colonized N. America (can be found on the Belmont campus and as far north as the Canadian border).

C. Placentals - young develop in the uterus each with an umbilical cord attached to a placenta which serves as an organ of respiratory gas and nutrient/waste exchange; placenta(s) are usually delivered a few minutes after viviparous partuition (live birth; did your Dad get to cut the umbilical cord???).

Males have the usual marsupial placement of testicles, between the navel and the penis.

Like - did anyone ask the MONOTREMES what they wanted to be?