L. crassicaudata crassicaudata
|Lutrine opossum range|
The lutrine opossum (Lutreolina crassicaudata), also known as the little water opossum, thick-tailed opossum, or coligrueso is an opossum species from South America and is monotypic in the genus Lutreolina.
The lutrine opossum ("lutrine" means "otter-like" and "crass" meaning "thick, fat" and "cauda" meaning "tail") is a very peculiar opossum, having a long weasel-like body, short legs, small rounded ears, and dense reddish or yellowish fur. Nocturnal and crepuscular, they generally live in grasslands and savannas near water. They are terrestrial but are excellent swimmers and climbers.
Range and habitat
Lutreolina crassicaudata is found in Brazil, Argentina, Bolivia, Uruguay, Paraguay, Colombia and Guyana. Populations in the two last countries are isolated from the populations of all the other countries. It can be found in grasslands, savanna grassland, and gallery woodlands with permanent water bodies, in marshy or riparian habitats. They build tight nests made of grass and reeds or utilize abandoned armadillo or viscacha burrows 
With a skull adapted for carnivory, Lutrine opossums are carnivorous and insectivorous feeding on small rodents and lagomorphs, birds, insects, small crustaceans. They are considered to be the most carnivorous of all the members of the order Didelphimorphia. Captive populations have been observed eating butterfish mixed with meat, frogs, earthworms, shrimp at mice. Populations located close to urban areas have been known to scavenge through garbage but this behavior is isolated to these populations and likely occurs due necessity because there is less available prey in urban areas.
Fossils found in Minas Gerais, Brazil indicate that L. crassicaudata emerged in the late Pleistocene epoch. Lutreolina fossils found in Tarija, Bolivia as well as samples uncovered across Argentina also indicate appearance of lutrine opossum ancestors during the late Pleistocene. For a short time in Argentina, the opossums were hunted for their pelts for fur trade and to line garments. But this market quickly declined because the color of the opossum pelts would fade over time.
Breeding begins in September and carries on until April follow by approximately fives months of anestrous, or time without estrus. Lutrine opossums have two breeding periods per year resulting in litters of 7-11 offspring. Like all marsupials, litters are born into a pouch and are fed via lactation until the offspring is developed enough to leave the pouch. Gestation lasts approximately two weeks and young are weaned off mother's milk at around 3 months. The first litter is born in September and the second in December or January. The offspring from this breeding season reach sexual maturity at 6 months but don't begin reproducing until the following year. Males are heavier than females indicating sexual dimorphism likely caused by male-male competition for mates.
Lutrine opossums are quadrupedal and extremely agile. Although they are primarily terrestrial they are also adept climbers and swimmers. Their long body, proportionally short limbs, and no undulation of the vertebral column disqualifies them from being categorized as a specialized semi-aquatic mammal. Although they cannot be classified as truly specialized mammals, they are still considered strong swimmers drawing power from the hind limbs as the forelimbs paddle. By employing a variety of gaits their locomotion abilities allows them to run, walk, climb, swim through all the different kinds of obstacles found in the grassy-woodland and marshy areas in which they live. They can dive and swim with ease, expanding their prey base to aquatic invertebrates.
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