20 



NORTH AMERICAN FAUNA 75 



Metachirus nudicaudatus 

 Brown Four-eyed Opossum, Zorro de Cuatro Ojos 



Brown four-eyed opossums are found from southeastern Nicaragua through 

 much of South America to northern Argentina. Although Hall (1981) suggested 

 that the range of brown four-eyed opossums included all of Costa Rica, until recentiy 

 no specimens had been reported in the literature from Costa Rica. McPherson et al. 

 (1985) noted that one specimen was collected at Angostura, near Turrialba in 

 Cartago Province in 1876, and that for more than a century it went unrecognized 

 as being the only specimen of Metachirus nudicaudatus from the country. They 

 also reported a second specimen collected near Sarapiqui in Heredia Province in 

 1983. These specimens are from 600 m and 200 m, respectively, both from the 

 Caribbean slopes. 



Several individuals have recorded observations of animals they considered to 

 be M. nudicaudatus at La Selva over the years. We believe that most, if not all 

 of these observations were actually sightings of gray four-eyed opossums {Philander 

 opossum) . Although M. nudicaudatus and P. opossum are similar in size {Meta- 

 chirus is slightly smaller) and appearance, they are not particularly closely related. 

 The only field character useful in separating these two species is that Metachirus, 

 as its common name implies, is various shades of brown, whereas Philander, as 

 its common name implies, is various shades of gray. These two species are dif- 

 ficult to distinguish in the field, especially at night under poor light. The use of 

 the name M. nudicaudatus for all four-eyed opossums at La Selva seems to be 

 based on a 1960's handwritten list of the mammals occurring there, where the 

 species is listed as the only four-eyed opposum of the region. It seems likely that 

 subsequent observers applied this name to any four-eyed opossums they observed, 

 even though Philander is actually more abundant and thus more likely to be ob- 

 served. Given the apparent rarity of M. nudicaudatus in Costa Rica, it would be 

 extremely valuable to have additional specimens of four-eyed opossums available 

 for study. 



Additional record (1)— Sarapiqui, Finca Cantarrana, near Rio Peje, 200 m 

 [1 male, MNCR— McPherson et al. 1985]. 



Philander opossum 

 Gray Four-eyed Opossum, Zorro de Cuatro Ojos 



Gray four-eyed opossums are found from eastern Mexico south throughout 

 Central America and much of tropical South America (Fig. 9). The subspecies 

 Philander opossum fuscogriseus is found in Costa Rica from sea level to about 

 1,600 m. 



On 14 April, an adult male P. opossum was captured crossing a fallen log 

 near the Rio Cascante at 680 m. External measurements for this male are: total 

 length, 625 mm; length of tail, 310 mm; length of hind foot, 48 mm; height of 

 ear from notch, 40 mm; weight, 605 g; testes measured 15x10 mm. 



A fresh partial skull of a second adult P. opossum was found along the Rio 

 Cascante at 680 m; it appeared that the animal recently had been consumed 



