Viera's Spiny Tree Rat

Vieira's spiny tree-rat is a small rat, with an average adult head and body length of 24.5 centimeters (9.6 inches) and average tail length of 34 cm (13 in). It is covered in stiff, bristled fur, dark brown above and light brown underneath. The brown fur is dull throughout most of the body, but gets darker towards the head. Among members of the Echimyidae family, the genus Echimys has some of the most spinose guard hairs or spines, meaning that they are very stiff and robust and have blunt tips. The purpose of these hairs and differences within the family in terms of guard hair softness is thought to be tied to ancestral habitat preference and need for thermoregulation, as softer, denser fur is better at holding on to warmth. Its main diagnostic trait is the presence of a dark maroon stripe on the median of the head, running down the back. As compared to the white-faced spiny tree-rat (Echimys chrysurus), the fur on the back of Vieira's spiny tree-rat is darker. Vieira's spiny tree-rat can be distinguished from the dark spiny tree-rat (Echimys saturnus) by its distinctly separate dark head and lighter-colored back, while E. saturnus is more uniformly black in these areas. E. saturnus also has a gray or spotted white underside, which is contrasted with the light brown fur seen in E. vieirai.

This spiny rat is known to occur in the Brazilian states of Amazonas and Pará. Based on the two localities where it has been found, the species is presumed to inhabit mature lowland rainforests.

As little specific information is known about Vieira's spiny tree rat, much is assumed based on the life history of similar rodents. It is presumed to be arboreal and nocturnal, and its diet is likely made up of fruits, leaves, and potentially arthropods.