Australian.Geographic_2014_01-02

56 Australian Geographic

 T

HE DUGONG IS the only

surviving species in the family

Dugongidae. There was one other

modern member – Steller’s sea cow; a huge,

slow-swimming northern Pacific mammal

that ate seaweed and may have reached

weights of up to 10 tonnes. Sadly, the

species is now best known as a cautionary

conservation tale: it was discovered and

hunted to extinction in three decades

during the 18th century.

Dugongs belong to the order Sirenia (the

sirens), the name being a nod to mermaid

mythology. The other living members are

three species of manatee, all found in coastal

areas and rivers of the Caribbean Sea and

Gulf of Mexico, the Amazon Basin and West

Africa. There are similarities between the two

groups, particularly their size, appearance

and histories: they are both long-lived, slow

breeders that spend much of their time

grazing on aquatic plants. But, in the evolu-

tionary sense, they’ve been separated for a

long time and there are significant differenc-

es. Manatees have a broader diet, consuming

a wider range of plant material, including

mangrove leaves and fish. Dugongs are strict-

ly marine creatures, but manatees also inhabit

estuarine and freshwater habitats.

Sirenians have a similar shape to whales,

dolphins or seals, but are not closely related.

They have a clearer evolutionary connection

to elephants and small rodent-like animals

called hyraxes, found in Africa and the

Middle East.

Sirenians the World

Although you could be forgiven for thinking these ‘sirens’ are closely related to whales, this

order of marine creatures actually has closer ties to the largest land mammal, the elephant.

Trichechus manatus

An estimated 10,000 animals

in two subspecies of West

lndian manatee survive in

waters off Florida, USA, the

Caribbean Sea and Gulf of

Mexico. Unlike their close

relatives, dugongs, man-

atees can tolerate a wide

range of salinities and will

move easily between fresh-

water rivers and the sea.

West Indian

manatee

Trichechus inunguis

This dark-skinned mammal, described as

looking like both a seal and a hippopot-

amus, is the smallest of the manatees

and the only one to be restricted to fresh

water. It occurs only in the Amazon River

and its tributaries, and is believed to be

critically endangered.

Amazonian

manatee