The New Neotropical Companion

America also boasted a diverse marsupial community.

Today, though, just over 40 species of opossums are

found in the Neotropics, most of the original South

American marsupial fauna is extinct. During the

Pleistocene faunal exchange (chapter 8) a few species

migrated northward, including the durable Virginia

Opossum (Didelphis virginiana; plate 8- 46), which

continues to expand its population in North America

today. However, many placental mammals emigrated

from the north into South America, and their arrival

coincides to a degree with a decline in richness of

marsupials. South America’s marsupial fauna is but a

remnant of what it once was.

The Common Opossum (D. marsupialis), found

throughout Central America and Amazonia, has

hardly changed in appearance from its ancestors who

roamed the planet 65 million years ago. The fossil

record indicates that the opossum family (Didelphidae)

dates back to the Late Cretaceous period, while the

Common Opossum species arose about 35 million

years ago. That means, of course, that early opossums

were contemporary with the last of the dinosaurs.

Superficially rat- like, with a pointed snout and scaly

naked tail, the Common Opossum weighs between

2.3 and 4.5 kg (5– 10 lb) and is largely gray, with some

black. It inhabits almost any kind of terrestrial habitat

other than desert and high mountains. Opossums are

excellent tree climbers and often hang upside down,

clinging by their prehensile tails. Totally omnivorous,

the opossum will try eating almost anything. Its most

remarkable behavior, “playing possum,” is an act in

which the animal feigns death when it is threatened.

In addition to the Common Opossum, the

Neotropics host numerous other opossums. Most are

nocturnal, but many are common and seen relatively

often in daytime. There are tiny mouse opossums

(Marmosops, Micoureus, Gracilinanus, Marmosa;

plate 16- 60), furry little woolly opossums (Caluromys;

plate 16- 61), bushy- tailed opossums (Glironia), four-

eyed opossums (Philander, Metachirus), which are

four- eyed in name only, short bare- tailed opossums

(Monodelphis), and the Yapok, or Water Opossum

(Chironectes minimus). Though these species are

different sizes, they are all basically similar in anatomy,

and the group ranges throughout the various habitats

of Central and South America. What this diversity

indicates is that opossums have undergone a successful

adaptive radiation throughout the American tropics

and are the survivors of what was, for other marsupials,

a bygone era.

Plate 16- 61. Like other opossums, the Central American

Woolly Opossum (Caluromys derbianus) is fundamentally

arboreal and active mostly at night. Photo by James Adams.

Plate 16- 60. It is easy to see why this tiny animal is called a

mouse opossum. The species pictured is Mexican Mouse

Opossum (Marmosa mexicana). Photo by James Adams.

chapter 16 from monkeys to tarantulas: endless eccentricities 345