Earless water rat

The earless water rat (Crossomys moncktoni) is a special kind of rodent that lives in New Guinea. It belongs to a group called Hydromys, which is part of the larger family of Old World rats and mice (Murinae). This animal is the only species in its own group, called the genus Crossomys. Scientists think it might be most similar to another rodent named Baiyankamys, but they are still learning more about its family connections.

What makes the earless water rat really special is how well it can live in water. It is one of the best water-loving rodents in the whole world, spending much of its time swimming and moving easily through rivers and lakes. This amazing ability helps it survive in its wet home.

Names

This animal is called kuypep in the Kalam language spoken in Papua New Guinea.

History of discovery

This animal was first described in 1907 by a British scientist named Oldfield Thomas. He studied one specimen caught by a man named Mr. C. A. W. Monckton near Brown River in Central Province, in south-east Papua New Guinea. The animal was named after Monckton. Another specimen was found in July 1950. Since then, a few more have been caught in the mountains of eastern New Guinea, but this animal is still quite rare. Its scientific name means "Monckton's fringed mouse", honoring the person who collected the first specimen and describing the fringe of hairs on its tail.

Relationships

Scientists have studied how the earless water rat is related to other rats. Some believed it was closely related to the genus Hydromys, but later studies suggested it might be closer to other genera like Leptomys, Pseudohydromys, and Xeromys.

American scientists Guy Musser and Michael Carleton placed the earless water rat in the Hydromys group because its body structure is more similar to this group than to the Xeromys group. More recent research suggests that the earless water rat is most closely related to another genus called Baiyankamys.

Characteristics

The earless water rat is very well suited for life in water. It has very long hindfeet with webbed toes, tiny front legs, and no visible ears. Its eyes are small, and it has a long tail with special rows of hairs along the bottom.

Its back is a greyish brown color, while its belly is white. The fur is soft and helps keep it dry. The top half of its tail is light grey, and the bottom half is white. The earless water rat is about the same size as its close relative, Baiyankamys.

Distribution, habitat and behavior

The earless water rat lives in the mountains of Papua New Guinea, specifically in the Central Cordillera and the Huon peninsula, at heights between 1000 to 2700 meters above sea level. It prefers cold, fast-flowing mountain streams.

During the day, this rat hunts for food such as tadpoles, worms, and river insects, especially their larvae. At night, it rests in holes along the riverbank. Each time, the earless water rat has only one baby. Local hunters sometimes catch it when river levels are low. Different tribes have their own names for this animal, such as kwypep for the Kalam tribe in Madang Province and possibly ogoyam in the Telefol language from Sandaun Province. The animal is also called momo by the Rofaifo in Southern Highlands Province, though this name is used for other water rats too, like the common Rakali. Some names mean "water sugar glider" because of how its fur looks.

Not much is known about how safe this animal is, but it is considered to be of "least concern" by the IUCN Red List.