Choloepodidae, Gray, 1871

Mora, José Manuel & Ruedas, Luis A., 2023, Updated list of the mammals of Costa Rica, with notes on recent taxonomic changes, Zootaxa 5357 (4), pp. 451-501 : 456-457

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.

Figures

FIGURE 1. Plot of number of species known (vertical axis) by year of publication of taxonomic compendium for mammals of Costa Rica. See text for publication details of the taxonomic compendia. The data suggest that over the past 154 years, the number of species of mammals known for Costa Rica has accumulated at a rate of 1.2 species year-1 in two major pulses (1869 to 1946: 1.73 spp. yr-1, R2 = 0.99; and 1983 to 2023: 1.64 spp. yr-1, R2 = 0.98) and is not experiencing any reduction at present.

FIGURE 2. Distribution of species of Costa Rican mammals by categories of threat as assessed by the International Union for the Conservation of Nature (IUCN). A: overall assessment of all mammal species known for Costa Rica into IUCN categories of threat. Key to abbreviations: EN, endangered; DD, data deficient; LC, least concern; NT, not threatened; VU, vulnerable. B: Trends in population growth rates for the 202 species of Costa Rican mammals listed in the IUCN category of “least concern.” C: Trends in population growth rates for all Costa Rican mammal species. Numbers represent total number of species in each category followed by proportional representation relative to the total, expressed as a percentage.