The phylogenetic position of conodonts, known in the fossil record from the Cambrian to the Late Triassic and important as biostratigraphic indicators, has long been subject to much speculation. Some earlier workers thought that they might be related to early fishes (and therefore included in the chordates in Nelson, 1976). It has only been since the early 1990s, with the discovery of fossilized soft body parts, evidence of cellular bone, and a study of tooth histology, that convincing evidence has been published that they are craniates (but see Kemp, 2002, for evidence that they do not contain hard tissues characteristic of vertebrates), although I credit a 1987 study of R. J. Krejsa and H. C. Slavkin with providing evidence that they have a relationship to hagfishes. Conodonts were placed between the cephalochordates and the cra-niates in Nelson (1994), in the subphylum Conodontophorida. Placement here is based on Donoghue et al. (2000), who give a detailed discussion of their anatomy and placement. Conodonts are reviewed by Aldridge and Donoghue (1998), with additional information in Purnell et al. (2000).
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