The Collaborative International Dictionary of English v.0.48:

Mammutidae \Mammutidae\ prop. n.
   An extinct natural family of mammals, comprising the
   mastodons.

   Syn: family Mammutidae, family Mastodontidae.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Mammutidae
    n 1: extinct family: mastodons [syn: Mammutidae, family
         Mammutidae, family Mastodontidae]