Geoscience Reference
In-Depth Information
.................................................
The Last of the Edentates
The mammal group Xenarthra's origins can be
traced back as far as the early Tertiary Period
(60 mya), shortly after the decline of the dino-
saurs. It is represented by three families: ant-
eaters, sloths, and armadillos. They are the last
remaining families of a large group of animals
that evolved in South America when it was an
isolated continent. With few exceptions, all
members of these three families only occur in
the Neotropics. All tend to be specialized
feeders, eating mainly termites and ants, or
rainforest canopy leaves.
Three genera and four species of anteaters
are only found in the Neotropical rainforest.
They are the giant anteater, collared anteater
and tamandua (in the same genus), and the
pygmy or silky anteater. Anteaters have no
teeth, but a long tubelike snout and a sticky
tongue that can be greatly extended to trap
insects.
Two genera of the sloth family, the three-
toed and two-toed sloths, exist solely in the
Neotropical forests. Five species have been
identified. The brown-throated and pale-
throated three-toed sloths have a wide distri-
bution in the Neotropical rainforest, while the
maned three-toed sloth has a limited distribu-
tion along the Atlantic coast of Brazil. The two-
toed sloths include Hoffman's two-toed sloth in
Central and South America, with a disjunct
population in southern Peru, and the southern
two-toed sloth in South America. Sloths are
found nowhere else in the world. The group
Xenarthra also contains eight families of extinct
ground sloths and armadillo-like mammals
such as the giant sloth and glyptodont of the
Pliocene Epoch.
.................................................
coarse hair is a layer of thick fur, which protects
the sloth from the bites of tropical ants that try to
vigorously protect some of the trees sloths visit reg-
ularly, such as the cecropia tree. Sloths seems little
affected by the ants. Three-toed sloths have long
and sharp claws that are used to grip into the trees
and to slash out at an enemy when threatened.
Although sloths are strictly arboreal, they will
descend to the ground once a week to urinate and
defecate, or to move to a more distant tree. On
the ground, the sloth is vulnerable to predation
from jaguars and anacondas. An even more for-
midable predator is the Harpy Eagle that locates a
resting sloth while perched high in an emergent
tree. The eagle swoops down and with its great
talons easily and rapidly seizes the sloth.
In the rainy season, the sloth's hair has a
greenish hue caused by microscopic blue-green
algae that grow on its back. Along with algae, the
sloth's hair is home to the pyralid moths whose
adults live on their backs and feed on the algae
growing there. Pyralid moths lay eggs in sloth
dung where the larvae later hatch and feed. When
the adult moth emerges, they fly up into the trees
to find a new sloth host, and the cycle begins
again. Other arthropods also live on sloths,
including flies, mites, and beetles.
Sloths are endangered due to habitat destruc-
tion throughout the rainforests. Their populations
are particularly vulnerable in Brazil, where forests
are being destroyed at a rapid pace.
Several armadillos occur in the Neotropical
rainforest, including the giant armadillo, the
northern and southern naked-tailed armadillos,
the yellow armadillo, and three different long-
nosed armadillos. With the exception of the nine-
banded long-nose armadillo, common in the
southern United States, all are restricted to Cen-
tral and South America. Like anteaters, armadil-
los specialize in ants, termites, and other forest
insects. Larger armadillos have been hunted for
meat, while smaller ones have been hunted for their shells, used in making a gui-
tar-like string instrument in parts of South America.
