White-faced spiny tree-rat

The white-faced spiny tree rat was first described by German zoologist Eberhard August Wilhelm von Zimmermann in 1780, who drew upon the Swiss-Dutch natural philosopher Jean-Nicolas-Sébastien Allamand's 1778 addition to the Histoire Naturelle^[5] titled "Le Lerot à queue dorée". Zimmermann gave the species the scientific name of Myoxus chrysurus and wrote that its type locality was in Suriname. The taxonomy of the white-faced spiny tree rat changed often throughout the 18th and 19th centuries; Allamand initially placed the species in the genus Hystrix, the Old World porcupines, and later authors would assign it to Glis, Loncheres, and Nelomys^[6] before the currently accepted name, Echimys chrysurus, was assigned by Swiss naturalist Heinrich Rudolf Schinz in his 1825 translation of Le Règne Animal.^[7] According to genetic analysis, the species is closely related to the dark spiny tree-rat (Echimys saturnus).^[8]

The etymology of the species name derives from the two ancient Greek words χρυσός (khrusós), gold, and οὐρά (ourá), animal tail.^[9][10] The genus name Echimys, and also its synonym Echinomys,^[11] derive from the two ancient Greek words ἐχῖνος (ekhînos), meaning "hedgehog", and μῦς (mûs), meaning "mouse, rat".^[9][10]

The white-faced spiny tree-rat is found throughout Guyana, Suriname, and French Guiana. It is known from the eastern Amazon Basin, but occurs south of the Amazon and east of the Xingu River in parts of Brazil.^[1]

Vine-covered areas of lowland rainforests are the preferred habitat of the white-faced spiny tree-rat. It is a strictly arboreal species; it resides in the middle and upper strata of the rainforest and is found at elevations ranging from sea level up to about 200 metres (660 feet).^[6] It is also known to live in open, primary forests.^[1]

White-faced spiny tree-rats typically weigh up to 760 grams (27 ounces) and have a head-body length of 24 to 33 centimetres (9.4 to 13.0 inches). The tail ranges in length from 25 to 40 cm (9.8 to 15.7 in), typically measuring 120% of the rodent's head-body length. It is covered in hair and turns from brown to white towards the tip.^[6] The rat's fur is made up of a mixture of broad, heavy spines and dark hairs that are brown at the tip and grey along the shaft. The fur near the back of the head is often darker than that along the rest of the animal's body.^[12] The small ears of the white-faced spiny tree rat are slightly haired and brown. Its eyes are dark brown and have a red eye shine. The broad feet are covered with brown fur on top, and each digit has a claw.^[6]

The main diagnostic character state or trait of this species is the presence of a white stripe on the head. As compared to Echimys vieirai and E. saturnus, the fur on the back of the white-faced spiny tree-rat is brighter.^[13] The species is distinguished from other members of Echimys by several characteristics of its skull: its auditory bullae, bony structures that contain the inner ear, are of medium to small size, the external auditory meatus or ear canal is short, and it has a small internal auditory meatus, a bony canal connecting the inner ear to a cavity at the back of the skull (the posterior cranial fossa). The convex surface of the lower back of the skull, the squamous part of the occiptial bone, has short bony extensions on the lateral sides of the foramen magnum, an opening at the skull's back and lower part (the occiput). Nearby, the depression in the base of the skull known as the jugular fossa is broad and deep. Small, nearly circular openings or fenestrae are present ahead of (anterior to) the ear canals. The septum of the premaxillary bone, at the very tip of the upper jaw, is incompletely separated towards the back. The white-faced spiny tree-rat has parallel, rectangular rows of teeth, and its cheek teeth are longer than they are wide. The species' lower molars are very similar to those found in other tree-dwelling spiny rats (members of the family Echimyidae).^[6]

White-faced spiny tree-rats are nocturnal animals. They produce two young in a litter.^[1] When startled by human or predator activity, they will move quickly across branches, but typically have a slow pace of movement. The species feeds on fruit, foliage, and some insects, mainly arthropods.^[6] One known predator of the species is the ornate hawk-eagle.^[14]

The white-faced spiny tree-rat has a stable population trend. It is potentially threatened by deforestation, though the 2016 report produced by Catzeflis and Patton for the International Union for Conservation of Nature (IUCN) did not consider this to be a major issue. They classified the species as least concern due to its wide distribution and presence in several protected areas.^[1] It was previously classified as vulnerable in the 1996 issue of the IUCN Red List due to a perceived population decline caused by loss of habitat and threats by introduced species in Brazil.^[15] Few museum specimens and ecological studies of the species exist.^[6]