Choloepus didactylus (Linnaeus)

VOSS, ROBERT S., LUNDE, DARRIN P. & SIMMONS, NANCY B., 2001, The Mammals Of Paracou, French Guiana: A Neotropical Lowland Rainforest Fauna Part 2. Nonvolant Species, Bulletin of the American Museum of Natural History 2001 (263), pp. 1-236 : 64

Choloepus didactylus (Linnaeus)

VOUCHER MATERIAL: AMNH 265952, MNHN 1995.952. Total = 2 specimens.

IDENTIFICATION: Although the species­level taxonomy of two­toed sloths, genus Choloepus , has never been formally revised, two species are consistently recognized in modern synoptic treatments of edentate classification (e.g., Wetzel and Ávila­Pires, 1980; Wetzel, 1982, 1985); of these, only C. didactylus is known to occur in the Guiana subregion of Amazonia. Our voucher material conforms with the brief description of topotypic specimens of C. didactylus from Surinam provided by Husson (1978), and with the cranial diagnosis of this species provided by Wetzel (1985). However, the fur on the throat of our adult female specimen (AMNH 265952) is distinctly paler and shorter than the pectoral fur, a pelage trait that Wetzel regarded as diagnostic of C. hoffmanni (from western Amazonia and Central America). The throat fur of our juvenile male (MNHN 1995.952) is likewise paler than the chest fur, but the contrast is less marked than in the adult female. For comparison with Surinamese topotypes measured by Husson (1978: table 38), external measurements of our adult female voucher were 698 Χ 12 Χ 164 Χ 29 mm, and it weighed 7.3 kg. Selected cranial measurements of this specimen are: condylobasal length (‘‘greatest length of skull’’), 119.1 mm; zygomatic breadth, 73.0 mm; interorbital constriction, 36.3 mm; alveolar length of maxillary toothrow, 44.5 mm. The ratio of the minimal to the maximal interpterygoid width (after Wetzel, 1985) in this specimen is 0.49.

FIELD OBSERVATIONS: Two­toed sloths are probably common at Paracou. P. Petronelli (personal commun., 1993) estimated that the species is sighted by forestry workers about five or six times a year in our study area, a reasonably high frequency given its cryptic appearance and inconspicuous habits. Of five sightings by inventory personnel from 1991 to 1994, four were nocturnal and one was diurnal: (1) RSV found a lactating female and a juvenile male (the vouchers described above) hanging together motionless in subcanopy vegetation (ca. 20 m above the ground) in well­drained primary forest at 20: 15 hours on 30 July 1991. (2) RSV found a large adult of undetermined sex descending a tree head­first (probably to defecate) in well­drained primary forest at ca. 23:00 hours on 6 August 1991; the animal was about 2 m above the ground and remained motionless throughout the encounter (about 10 min), even when touched; its eyeshine was very faint. (3) RSV saw another solitary adult of unknown sex sleeping suspended from a liana ca. 4 m above the ground in old secondary growth at 02:00 hours on 31 July 1993. (4) L. H. Emmons saw a solitary animal of unknown sex climbing rapidly about 20 m above the ground in well­drained primary forest at 10:15 hours on 24 September 1994. (5) L. H. Emmons found an adult of unknown sex hanging motionless under a branch about 20 m above a stream in primary forest at 20:21 hours on 5 October 1994.