In the context you provided, "abstract" is used to describe the nature or style of a sculpture. An abstract sculpture is a type of art that does not attempt to represent objects or figures in a realistic way but instead uses shapes, forms, and colors to create a non-representational or non-literal representation of an idea, concept, or emotion. So, when it mentions "one an abstract, plated mammoth," it means that the sculpture is in the shape of a mammoth but is not a realistic or lifelike representation of a mammoth; instead, it's created in an artistic, non-realistic style.