Marsupials

By | September 9, 2016

The earliest mammals reproduced by laying eggs, but by the Cretaceous Period mammals had evolved new ways of reproducing. The marsupials and their close relatives gave birth to tiny babies that developed outside the mother’s body, often in a pouch. Today, most marsupials are found in Australia, but in the past they were very common in South America and Antarctica too.

FAMILY FACT FILE

Key features of marsupials
■ Give birth to tiny, immature babies
■ Babies usually develop inside a pouch
■ Four pairs of molar teeth
■ Furry or hairy body
■ Mothers produce milk for young

When
Marsupials first appeared in the Early Cretaceous (about 125 million years ago). Today, there are close to 300 marsupials, including kangaroos, wombats, and koalas.

Thylacosmilus (THIGH-lah-coe-SMILE-us)

thylacosmilus


When: 10–2 million years ago (Neogene)

Fossil location: S. America

Habitat: Woodlands

Length: 5 ft (2 m)

Diet: Meat

Thylacosmilus looked just like a sabertoothed cat, but it was a close relative of the marsupials. It was the size of a jaguar and built like a cat, but details of its skeleton show it was more like a giant opossum than a member of the cat family. Its huge canine teeth rested on odd-looking bony extensions of its chin, and unlike the teeth of cats they never stopped growing.

KILLER TEETH

Thylacosmilus-skull

Two long, saber-shaped teeth pointed downward from Thylacosmilus’s upper jaw. They were protected by tooth guards made of bone.


Diprotodon (die-PRO-toe-don)

diprotodon


When: 2 million–40,000 years ago (Neogene)

Fossil location: Australia

Habitat: Forest and scrubland

Length: 10 ft (3 m)

Diet: Plants

Also known as the giant wombat, rhinocerossized Diprotodon was the largest marsupial known. A plant-eater, it survived on a mixture of rough leaves and grasses and may have lived in herds. Fossils of female Diprotodons carrying young reveal that babies’ pouches opened toward the rear, unlike the forward-facing pouches ofkangaroos.
Diprotodon disappeared shortly after humans first colonized Australia.
Some scientists think it was hunted to extinction for its meat, though others blame loss of forest as Australia’s climate gradually became more dry.

Argyrolagus (ar-JYE-roe-LAY-gus)

Argyrolagus


When: 23–2 million years ago (Paleogene–Neogene)

Fossil location: S. America

Habitat: Desert

Length: 1 ft (0.4 m)

Diet: Plants

Argyrolagus fossils dating back to 53 million years ago have been found in South America. This creature looked like a giant kangaroo rat, with very long hindlimbs and small forelimbs. It probably moved around by hopping, just like a modern kangaroo. Its long tail helped it to keep its balance. Argyrolagus’s narrow head had a pointed snout with broad cheek teeth, which it may have used for crushing tough plants and other vegetation.
This marsupial had big eyes for seeing in the dark and probably fed at night.

Sinodelphys (SIGH-no-DELF-iss)

sinodelphys


When: 125 million years ago (Early Cretaceous)

Fossil location: China

Habitat: Woodlands

Length: 6 in (15 cm)

Diet: Insects and worms

Judging by its teeth and by the bones of its wrists and ankles, this chipmunk-sized tree-dweller was closely related to the first marsupials, although it wasn’t a marsupial itself.
The single fossil, found in China in 2003, is well preserved and shows tufts of hair around the bones. Sinodelphys was a good climber, with flexible ankle bones—it could rotate its feet backward to climb down trees. It probably scurried around among the branches—safe from predators—chasing after insects.

LIVING RELATIVE

kangaroo-baby

Kangaroo mom carrying her baby in pouch

Kangaroos are the largest living marsupials and are found only in Australia and New Guinea. A kangaroo baby (a “joey”) is the size of a jellybean when born and is blind, deaf, hairless, and has no back legs. It squirms into its mother’s pouch and stays there for up to eight months, suckling from a nipple, until it develops fully.

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