形態に基づく分類体系では、ナマケモノ類はミロドン下目Mylodontaとメガテリウム下目Megatheriaに大別され、現生科はメガテリウム下目に含まれるとされていた[3][16]。上述するようにフタユビナマケモノ属は絶滅したメガロニクスを模式属とするMegalonychidae科に分類されていた[2]。以下の分類は、McKenna & Bell (1997) に従う[3]。
Alfred L. Gardner, “Order Pilosa,” In: Don E. Wilson & DeeAnn M. Reeder (eds.), Mammal Species of the World (3rd ed.), Volume 1, Johns Hopkins University Press, 2005, Pages 100-103.
Malcolm C. McKenna & Susan K. Bell, “Suborder Phyllophaga,” Classification of Mammals: Above the Species Level, Columbia University Press, 1997, Pages 93-102.
Janeene M. Touchton, Yu-Cheng Hsu, & Alberto Palleroni(2002).“Foraging ecology of reintroduced captive-bred subadult harpy eagles (Harpia harpyja) on Barro Colorado Island, Panama”.ORNITOLOGIA NEOTROPICAL13: 365–379.
P. F. SCHOLANDER, RAYMOND HOCK, VLADIMIR WALTERS, and LAURENCE IRVING. 1950. ADAPTATION TO COLD IN ARCTIC AND TROPICAL MAMMALS AND BIRDS IN RELATION TO BODY TEMPERATURE, INSULATION, AND BASAL METABOLIC RATE. The Biolgical Bulletin 99:259-271.
Frédéric Delsuc, Melanie Kuch, Gillian C. Gibb, Emil Karpinski, Dirk Hackenberger, Paul Szpak, Jorge G. Martínez, Jim I. Mead, H. Gregory McDonald, Ross D.E. MacPhee, Guillaume Billet, Lionel Hautier & Hendrik N. Poinar, “Ancient Mitogenomes Reveal the Evolutionary History and Biogeography of Sloths,” Current Biology, Volume 29, Issue 12, Elsevier, 2019, Pages 2031–2042.
Samantha Presslee, Graham J. Slater, François Pujos, Analía M. Forasiepi, Roman Fischer, Kelly Molloy, Meaghan Mackie, Jesper V. Olsen, Alejandro Kramarz, Matías Taglioretti, Fernando Scaglia, Maximiliano Lezcano, José Luis Lanata, John Southon, Robert Feranec, Jonathan Bloch, Adam Hajduk, Fabiana M. Martin, Rodolfo Salas Gismondi, Marcelo Reguero, Christian de Muizon, Alex Greenwood, Brian T. Chait, Kirsty Penkman, Matthew Collins & Ross D. E. MacPhee, “Palaeoproteomics resolves sloth relationships,” Nature Ecology & Evolution, Volumr 3, Issue 7, Springer Nature, 2019, Pages 1121–1130.