How are tree-kangaroos biologically confirmed as members of the class Mammalia?

Answer

They possess hair or fur, are warm-blooded, and nurse young with milk.

Tree-kangaroos are firmly placed within the class Mammalia because they exhibit fundamental traits such as possessing fur, maintaining a warm-blooded state, and producing milk via mammary glands to nurse their young.

How are tree-kangaroos biologically confirmed as members of the class Mammalia?
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