Dromiciops gliroides, (Thomas 1894, Marshall 1978) is the extant, monito del monte or colocolo opossum, a tiny living basal marsupial from South America. The middle ear (endotympanic + alisphenoid (epiterygoid) is greatly inflated. Image courtesy of Digimorph.org and used with permission. Click here for in vivo pictures on YouTube.

Gray JE 1821. On the natural arrangement of vertebrose animals. London Medical Repository 15(1):296–310.

Marshall LG 1978. Mammalian species, Dromiciops australis, American Society of Mammalogists, pp. 1-5. pdf

Thomas O 1894. On Micoureus griseus, Desm., with the description of a new genus and species of Didelphyidae. Ann. Mag. Natural History Ser 9, 3:199-212.

wiki/Dromiciops