An Australian relative in south America
In the temperate Valdivian and Patagonian forests of Chile and Argentina lives a small, mouse-like marsupial that rewrites the story of its kind. The monito del monte (Dromiciops gliroides), Spanish for "little monkey of the mountain," is the only living species of the ancient order Microbiotheria. Genetically, it is more closely related to Australian marsupials like kangaroos and koalas than to any other marsupial in the Americas. This connection makes the monito del monte a living fossil and an important piece of evidence for the ancient supercontinent of Gondwana.
The accepted theory is that marsupials originated in South America and migrated to Australia when the continents were connected via a forested Antarctica. The ancestors of the monito del monte represent the lineage that made this trans-Antarctic trek. The divergence between the Microbiotheria and the Australian marsupials is estimated to have occurred around 46 million years ago. While other South American marsupials belong to the group Ameridelphia, the monito del monte is the only New World representative of the superorder Australidelphia. Its existence provides a link to the deep past when these landmasses were one.
A keystone species of the forest
The monito del monte is a small, nocturnal creature, weighing between 16 and 42 grams with a body length of 8 to 13 centimeters. It is arboreal, living in the dense undergrowth of Chilean bamboo (Chusquea) within old-growth forests. It builds spherical nests from water-resistant leaves, lined with moss, inside tree cavities or other sheltered spots. Its diet is omnivorous, consisting mainly of insects, larvae, and pupae, supplemented with fruits during the summer.
This animal is important to its ecosystem. It is the sole seed disperser for the mistletoe Tristerix corymbosus. The seeds of this parasitic plant must pass through the monito's digestive system to germinate successfully. This mutualistic relationship, which may have co-evolved over 70 million years, is fundamental to the forest's health, as nearly 100 other species of birds and mammals depend on the mistletoe for food and shelter.
To survive the cold winters, the monito del monte undergoes true hibernation, a rare trait for a South American mammal. It stores fat in its prehensile tail, which can dramatically increase its body weight before it enters a state of torpor. During hibernation, its heart rate can plummet from an active 230 beats per minute to just 30.