Updated list of the mammals of Costa Rica, with notes on recent taxonomic changes Author Mora, José Manuel 0000-0002-1200-1495 Department of Biology and Museum of Vertebrate Biology, Portland State University, Portland, Oregon 97207 - 0751, USA. jomora @ pdx. edu, josemora 07 @ gmail. com; https: // orcid. org / 0000 - 0002 - 1200 - 1495 & Carrera de Gestión Ecoturística, Sede Central, Universidad Técnica Nacional, Alajuela, Costa Rica. josemora07@gmail.com Author Ruedas, Luis A. 0000-0002-4746-4799 Department of Biology and Museum of Vertebrate Biology, Portland State University, Portland, Oregon 97207 - 0751, USA ruedas @ pdx. edu; https: // orcid. org / 0000 - 0002 - 4746 - 4799 ruedas@pdx.edu text Zootaxa 2023 2023-10-20 5357 4 451 501 http://dx.doi.org/10.11646/zootaxa.5357.4.1 journal article 274292 10.11646/zootaxa.5357.4.1 9e8bd887-7adc-4534-bab5-8d85a0f80ceb 1175-5326 10063541 D80094AD-DD1D-4EDA-BFB6-8B453814FC46 Choloepodidae The two–toed sloths are based on “ Bradypus ” [= Choloepus ] didactylus Linnaeus 1758:35 , a taxon the range of which he erroneously ascribed to “Zeylona”, i.e., the modern island of Sri Lanka . Simpson (1945) grouped the genera Bradypus and Choloepus Illiger, 1811 together in the family Bradypodidae , within Pilosa (at the infraordinal level), as did Hoffstetter (1958) and Romer (1966) . Bradypus tridactylus Linnaeus 1758:34 remained in Bradypodidae when familial rearrangements began to affect the taxonomy of “ Bradypus ” didactylus following the suggestion by Guth (1961) , Patterson & Pascual (1968 , 1972 ), Webb (1985) , and Patterson et al . (1992) , that Choloepus and Bradypus were not each other’s sister taxa. In particular, Patterson & Pascual (1968) suggested that Choloepus was more closely related to Megalonychidae , whereas Bradypus was more closely related to Megatheriidae . Gaudin (1995) provided a robust morphological test of the hypothesis of a monophyletic Bradypodidae using 85 discrete osteological characters of the auditory region in 21 extant and extinct sloth genera, and confirmed that Bradypus and Choloepus were distantly related (e.g., Gaudin 1995:678; see also Fig. 1 in Raj Pant et al . 2014 ). Subsequent molecular studies of xenarthrans, including the orders Cingulata and Pilosa by Delsuc et al . (2001 , 2002 , 2003 , 2004 , 2012 ) and M̂ller-Krull et al . (2007), refined our contemporary understanding of the relationships among modern genera in the group. More recent mitogenomic data have provided not only resolution but a timeline of evolution for xenarthrans ( Gibb et al . 2016 ), but also confirmation of the distant relationship between Bradypus and Choloepus , and taxonomic localization of Bradypus in Bradypodidae and Choloepus in Megalonychidae . However, that latter study was based on extant taxa only. Incorporation of mitogenomes from extinct taxa of xenarthrans ( Delsuc et al . 2019 ) showed that Choloepus were the sister taxon to † Mylodontidae in a suprafamilial clade (Mylodontoidea) sister to another suprafamilial clade (Megatheroidea) that successively included † Megatheriidae , and Bradypodidae as sister to a clade including † Megalonychidae and † Nothrotheriidae (see Fig. 2 of Delsuc et al . 2019 ). As a result, here, we follow Delsuc et al . (2019) in adopting Choloepodidae for Choloepus species.