Changes in taxonomy

Both slender and slow lorises were introduced to European scientists by Dutch voyagers returning from Sri Lanka and the East Indies, which resulted in early references to such animals being unclear as to which genus was the subject of any given description.^[4]: 134 This trend would continue well into the late 1700s; Thomas Pennant illustrated a description of the slender lorises with that of a slow loris in 1781, and William Jones incorporated information pertaining to slender lorises into his 1795 description of slow lorises despite using a living slow loris as his reference. The earliest verifiable account of the slender lorises was produced by Jean de Thévenot during his visit to in India, which he based on two live specimens that were procured from Sri Lanka.^[5] Carl Linnaeus described slender lorises as Lemur tardigradus in the 1758 10th edition of Systema Naturae.^[4]: 134 Although the red slender loris is the type species of Linnaeus' Lemur, the term "lemur" has since been applied to lemuroids to the exclusion of other strepsirrhines.^[4]: 134 The trivial name tardigradus was adopted from Albertus Seba's description and illustration of the red slender loris,^[12] so named because it reminded him of sloths.^[3] Seba's description influenced Mathurin Jacques Brisson, who similarly concluded that slender lorises were sloths. Arnout Vosmaer echoed this sentiment in his 1770 description of a Bengal slow loris (Nycticebus bengalensis) that he mistakenly associated with slender lorises, which provoked a rebuttal from the Comte de Buffon, who disproved the sloth hypothesis by presenting slender lorises' primate traits in the seventh volume of Suppléments à l’Histoire Naturelle.^[5]

The first author to elevate Loris to generic status, thereby separating the slow and slender lorises into different species, was Pieter Boddaert in 1784,^[13] although his generic name, Tardigradus, was preoccupied. As such, taxonomic priority belongs to Étienne Geoffroy Saint-Hilaire's 1796 description of the Loris gracilis in the Magasin encyclopédique [fr].^[4]: 134 Geoffroy described Loris on the mistaken assumption that Linnaeus' Lemur tardigradus was a slow loris.^[12] Johann Karl Wilhelm Illiger authored a competing description of slender lorises, Stenops, in 1811.^[4]: 134 Expanding on Geoffroy's taxonomy, Gotthelf Fischer von Waldheim described a yellowish-brown loris as Loris ceylonicus in 1804.^[12] René Lesson authored his own description of the red slender loris, Arachnocebus lori, in 1840, which was a synonym of Linnaeus' description due to it also relying on Seba as its reference.^[12] Richard Lydekker established the first definitive taxonomic distinction between the red and gray slender lorises in 1905. Believing that two gray slender loris specimens from Chennai were representatives of the typical L. gracilis form described by Geoffroy in 1796, Lydekker described the red slender loris as L. g. zeylanicus.^[12] Ángel Cabrera attempted to correct Lydekker's error in 1908. Following the nomenclature of Eberhard August Wilhelm von Zimmermann's L. lori, Cabrera instead described the gray slender loris as L. lori lydekkerianus, with the red slender loris remaining as the type of the genus.^[12][14]

In 1913, Kathleen V. Ryley published a revision of the genus wherein she merged all then-extant Sri Lankan taxa into a single species, L. tardigradus, thereby returning to the Linnaean trivial name. She also elevated Cabrera's L. l. lydekkerianus subspecies to a species in its own right, which she named the Mysore slender loris (L. lydekkerianus).^[15][16] Robert Charles Wroughton later examined a female specimen from Kodagu that Ryley had described as a Mysore slender loris and instead described it as its own species, the Malabar slender loris (L. malabaricus), on account of its small size and unique pelage.^[16] In 1932, the slender lorises of Sri Lanka were divided into two subspecies by William Charles Osman Hill and William Watt Addison Phillips, who had found gray slender loris specimens 1,610 km (1,000 mi) higher in elevation than the recognized range of the red slender loris. They described this population as the Ceylon highland slender loris (L. t. grandis) on account of its large size, and described the red slender loris as a fellow subspecific member of a Sri Lankan species.^[12][17] The following year, Hill described the northern form of the Sri Lankan gray slender lorises as L. t. nordicus. Along with his description of a new subspecies, Hill found it necessary to revise the genus as a whole, as the northern Ceylonese slender loris (L. t. nordicus) appeared to occupy an intermediate position between all then-known forms of slender lorises. As such, he described the slender lorises as comprising a single species, L. tardigradus, with five different subspecies.^[12][14] He described a sixth subspecies, L. t. nyctibceboides, in 1942, which was based on a female specimen acquired from the Horton Plains by A. C. Tutein-Nolthenius in 1938.^[12][18] Hill's monospecific taxonomy was revised in 1998 by Colin Groves, who separated the red slender loris from the gray slender loris subspecies on account of morphological differences.^[12][19] A final subspecies, the northwestern red slender loris (L. t. parvus), was described by Saman Gamage et al. in 2017, who speculated that its morphological differences from the southwestern red slender loris may qualify it as an independent species, given further examination.^[12]

Diet

The slender lorises are one of the most faunivorous primates; the red slender loris has only been observed eating animal prey while the gray slender loris is primarily carnivorous (mostly insects) but will also eat bird eggs, berries, leaves, buds and occasionally invertebrates as well as geckos and lizards. To maximize protein and nutrient uptake they consume every part of their prey, including the scales and bones. They are able to digest toxic prey such as ants and noxious beetles, urinating on their hands before entering ant colonies to mimic the chemical profile of their prey to avoid attack.