ORDER SIRENIA: THE DUGONG AND THE
One of two fully aquatic ungulate
The manatees inhabit the large rivers
and Atlantic coastal waters of tropical Africa and America. The
dugong is found in the south-west Pacific and Indian oceans - mostly
in coastal areas but often in deeper waters.
Sea-cows have few competitors for
their sea-grass diet, perhaps turtles, but the silicate in their diet
forces the sea-cow to constantly replace its teeth. A very slow
metabolic rate permits submergence for long periods. Their flippers
and fluked tail are used for locomotion.
Today, sea-cows are threatened by
hunting, pollution and collisions with boats. Amazonian manatees are
being used to manage excess water weeds from dammed lakes which
prevent navigation, block turbines and destroy fisheries. Perhaps the
future is not so dim for at least some of the Sirenia.
|Cast of dugong skull|
The only front teeth on the skull of dugongs are
a pair of tusks (incisors). The remaining teeth are all set far back
in the jaw. The mouth opens on the underside for easy grazing. The
jaw of the manatee is less angled, and the teeth are constantly
replaced from the back of the jaw (as in elephants).
The dugong is a shy, poorly known
creature. The only true sea-going herbivore, Dugong travels in groups
from a single cow and calf to several hundred animals.
SIRENIAN EVOLUTION & THE
The earliest sea-cows are found in
Eocene deposits around the Tethys Sea (between Africa and Eurasia),
where they fed on the seagrass that grew in the tropical waters. From
here they spread as far as the Carribean and the Pacific
Strange as it may seem, the closest
relatives of the sirenains are the elephants. The Proboscidea and the
Sirenia are united by morphological features and protein/DNA sequence
studies The Orders Proboscidea and Sirenia are united in the taxon