Directions: Fill in the blank.

You may wonder how the expert on fossil remains is able to trace descent through teeth, which seem _____ pegs upon which to hang whole ancestries.

Inadequate means insufficient or not good enough. The sentence expresses skepticism that teeth seem like insufficient ('inadequate') pegs to hang entire ancestries on - suggesting doubts about whether teeth alone can support such extensive evolutionary claims. Reliable contradicts the skeptical tone, novel and specious don't fit the context.