australidelphia

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Sandstone dibbler (Pseudantechinus bilarni)
Also known as: Northern dibbler, sandstone false antechinus, sandstone pseudantechinus

The sandstone false antechinus was discovered in 1948 and described in 1954, when it was given the species name bilarni, which reflects the Aboriginal pronunciation of Bill Harney, an Australian writer and naturalist who accompanied the expedition that originally found it. It is an insectivorous species that, like many other dasyurids, so exhausts itself in the breeding season that most of the males die, although unlike some other species, about 25% of both sexes survive to a second year.

Classification
Animalia - Chordata - Mammalia - Metatheria - Marsupialia - Australidelphia - Dasyuromorphia - Dasyuridae - Dasyurinae - Dasyurini - Pseudantechinus - P. bilarni

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Monito del monte (Dromiciops gliroides)

The monito del monte is a diminutive marsupial native only to southwestern South America (Chile and Argentina). It is the only extant species in the ancient order Microbiotheria, and the sole New World representative of the superorder Australidelphia. The species is nocturnal and arboreal, and lives in thickets of South American mountain bamboo in the Valdivian temperate rain forests of the southern Andes, aided by its partially prehensile tail. It eats primarily insects and other small invertebrates, supplemented with fruit.

photo credits: José Luis Bartheld

While the monito del monte looks like an arboreal mouse or shrew, it’s actually a marsupial.  In particular, it’s a member of the superorder Australidelphia, the Australian marsupials, making it unique among the New World marsupials.  Study of its DNA, in fact, proved that Australidelphia originally evolved in South America, with all of them dispersing to Australia save the monito del monte’s ancestors.

joe-isnt-here-right-now  asked:

I have an interesting question for you Does anyone know how the Virginia Opossum ended up in North America yet no other marsupial species exists at all outside of Australia?

I’m afraid you have been sadly misinformed as to the geographic range of marsupials:

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Yeah. Let that sink in.

The truth is, there are 99 species of opossums that are endemic to the Americas. They belong to the superorder Ameridelphia (one of the two divisions of marsupials, the other being the Australidelphia for obvious reasons). A 100th species, the monito del monte, Dromiciops gliroides, belongs to the Australidelphia but is the only extant species of its entire order, and is also endemic to South America.

What is more, marsupials originated in the Americas[1].

I’ll give you a second to recover from this revelation.

They reached Australia somewhere between 100 and 66 million years ago, and subsequently radiated to their modern diversity[2]. This means that Antarctica was probably used as a channel for their dispersal, as it connected Australia and South America until around 65 million years ago (though opinions on dates differ). Although the fossil record is weak, the evidence points toward North America in fact being the origin of marsupials[2].

The Virginia opossum, Didelphia virginiana, belongs to the Didelphimorphia, the oldest extant lineage of marsupials[1,2]. This group is found exclusively in South America, with the exception of D. virginiana. Thus, in spite of the North American origin of marsupials, it is clear that D. virginiana was a secondary re-colonisation - and that is how it ended up in North America.

References:

[1] Nilsson, M.A., Charkov, G., Sommer, M., Van Tran, N., Zemann, A., Brosius, J. & Schmitz, J. 2010. Tracking Marsupial Evolution Using Archaic Genomic Retroposon Insertions. PLoS Biology 8(7):e1000436. [Open Access]

[2] Beck, R.M.D. 2008. A dated phylogeny of marsupials using a molecular supermatrix and multiple fossil constraints. Journal of Mammalogy 89(1):175-189