A Historical Reassessment of the Authorship Year of <i>Brachyteles arachnoides</i> (Primates: Atelidae)

The authorship of Brachyteles arachnoides has traditionally been ascribed to É. Geoffroy Saint-Hilaire, 1806. However, É. Geoffroy Saint-Hilaire's original description was based entirely on secondary accounts, namely, Browne's (1756) Simia 2 and Edwards' (1764) report of a brown, long-limbed, and four-fingered monkey, without directly examining specimens or illustrations. Browne's Simia 2 describes a large brown primate with a prehensile tail and four-fingered hands in Jamaica, characteristics that could apply to either Ateles or certain Brachyteles populations. Edwards' account, meanwhile, references two four-fingered "spider monkeys" observed in London but lacks sufficient detail for definitive taxonomic assignment. Historical trade data further undermine this link, as 18th-century Jamaica likely hosted Colombian/Panamanian primates, with no evidence of Brazilian primate imports. Étienne Geoffroy Saint-Hilaire obtained the first verifiable Brachyteles specimen only in 1808, seized during Napoleon's Lisbon campaign. His 1809 redescription, including an illustration and the specimen MNHN-ZM-2007-1475, meets modern taxonomic standards, whereas the 1806 name, based solely on ambiguous accounts, fails ICZN criteria for type association. We argue that Ateles arachnoides É. Geoffroy Saint-Hilaire, 1806, constitutes a nomen dubium, as it cannot be tied to verifiable material. Instead, we validate Ateles arachnoides É. Geoffroy Saint-Hilaire, 1809, with MNHN-ZM-2007-1475 as the holotype by monotypy. This redefinition stabilizes the species' nomenclature, anchoring it to a concrete specimen and Geoffroy Saint-Hilaire's empirically grounded 1809 work. By resolving these historical ambiguities, we provide a clearer framework for understanding Brachyteles taxonomy and highlight the importance of type specimens in early primatological classifications.