conodont

from WordNet (r) 3.0 (2006)

conodont
    n 1: the tiny fossil cone-shaped tooth of a primitive vertebrate
         of order Conodonta
    2: small (2 inches long) extinct eellike fish with a finned tail
       and a notochord and having cone-shaped teeth containing
       cellular bone; late Cambrian to late Triassic; possible
       predecessor of the cyclostomes

from The Collaborative International Dictionary of English v.0.48

Conodont \Co"no*dont\ (k[=o]"n[-o]*d[o^]nt), n. [Gr. kw^nos cone
   + 'odoy`s, 'odo`ntos, tooth.] (Zool.)
   A peculiar toothlike fossil of many forms, found especially
   in carboniferous rocks. Such fossils are supposed by some to
   be the teeth of marsipobranch fishes, but they are probably
   the jaws of annelids.
   [1913 Webster] Conodonta