The yellow-sided opossum (''Monodelphis dimidiata'') is an

opossum Opossums () are members of the marsupial order Didelphimorphia () endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 126 species in 18 genera. Opossums originated in South America and entered North A ...

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

from

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

. It is found in

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

and

Uruguay Uruguay, officially the Oriental Republic of Uruguay, is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast, while bordering the Río de la Plata to the south and the A ...

. They have grey or black fur on their dorsal side with yellowish fur on the lateral side that continues down to the feet. They are the most mysterious of all the ''Monodelphis'' that is found specifically in the Pampean region or

Pampa The Pampas (; from Quechuan languages, Quechua 'plain'), also known as the Pampas Plain, are fertile South American low grasslands that cover more than and include the Argentina, Argentine Provinces of Argentina, provinces of Buenos Aires Pro ...

of Argentina. It is suspected to be a once-in-a-lifetime breeder as seen in a three-year observational study of one population in the marshy grasslands of the Pampean region. Maintaining their native grasslands is important for them to keep a stable population. They show

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

in overall size: adult males are typically 100-150 g whereas adult females are 30-70 g.

Behavior

This species displays a rich repertoire of stereotyped behaviors. Postures, locomotion, and grooming are similar to those of other didelphids. They carry nest materials using their short but still

prehensile tail A prehensile tail is the tail of an animal that has Adaptation (biology), adapted to grasp or hold objects. Fully Prehensility, prehensile tails can be used to hold and manipulate objects, and in particular to aid arboreal creatures in finding and ...

s. Both males and females hunt insects and small vertebrates, and show specialized behaviors for dealing with difficult prey. Large insects are attacked rapidly and the head is consumed first. In contrast, hairy

caterpillar Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder ...

s are not immediately grabbed; instead, the opossum scratches the caterpillar to get rid of the

urticating hair Urticating hairs or urticating bristles are one of the primary defense mechanisms used by numerous plants, almost all New World tarantulas, and various lepidopteran caterpillars. ''Urtica'' is Latin for "nettle" (stinging nettles are in the genu ...

. Small mice are rapidly chased and attacked until a firm bite at the neck is attained, similar to the throat clamp used by large carnivores. ''M. dimidiata'' is thought to be a miniature analog to the marsupial sabertooths '' Thylacosmilus''. Like extinct sabertooth predators, it has one of the largest canines of any marsupial relative to body size and was proposed as a living model to test hypotheses about hunting strategies of the extinct predators.Blanco, R. E., Jones, W. W., & Milne, N. N. (2013). Is the extant southern short-tailed opossum a pigmy sabretooth predator?. Journal of Zoology, 291(2), 100-110. Yellow-sided opossums also show a variety of behaviors used in social contexts, including male-to-male agonistic rituals, and a variety of vocalizations whose social or adaptive significance deserves further investigation.

References

Short-tailed opossums Marsupials of Argentina Marsupials of Brazil Mammals of Uruguay Mammals described in 1847 Taxa named by Johann Andreas Wagner {{marsupial-stub