関連ワード:  why is duck billed platypus a mammal    why is a duck billed platypus called a mammal when it lays eggs    why is a duck billed platypus called a mammal    why is a duck billed platypus an unusual mammal    why is duck billed platypus called a bridge animal    why is a duck billed platypus called a primitive mammal    why is duck billed platypus called a bridge animal class 9    is duck billed platypus a true mammal    is duck billed platypus a sea mammal    is a duck billed platypus a mammal that lays eggs