Question: How old is the fossil record of the order that contains the only strictly marine herbivorous mammal?
Sentence (from "Xenastrapotherium"): It is a member of the family Astrapotheriidae in the subfamily Uruguaytheriinae, large astrapotheres, equipped with a trunk-like nose and protruding teeth, similar to the elephants, but their tusks were the canine teeth, not the incisors.
Relevant evidence: No