Australia: The Land Where Time Began

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Conodont-Vertebrate Phylogenetic Relationships Revisited

An evidence-based reassessment of the phylogenetic relationships of conodonts by Turner & Burrow has shown that conodonts are not “stem” gnathostomes, vertebrates or craniates. According to Turner & Burrow there is a significant group of workers studying conodonts that have proposed or accepted a designation of craniate for the conodont animal, and this interpretation is increasingly becoming established as accepted “fact”. The conclusion of Turner & Burrow, against this trend is that based on a revised cladistics analysis of traditional morphological features of both discrete conodont elements and apparatuses, histological investigation, and a revised cladistic analysis that modified that used in the keystone publication that has been promoted as proof of the hypothesis that conodonts are vertebrates. The results of the study by Turner & Burrow suggests that conodonts were possibly not even chordates, but Turner & Burrow demonstration of this is beyond the scope of this paper. In summary there is low cephalisation in conodonts; the presence of simple V-shaped trunk musculature and unique large-crystal albid in the elements; lack of dermal skeleton, including characteristic hard tissues of bone, dentine and enamel; lack of odontodes with bone attachment and a unique pulp system; lack of paraxial elements that are segmentally arranged and dermal elements in median fins, all of which, according to Turner & Burrow do not support a vertebrate or a craniate relationships for conodonts.

Conodonts are small animals that are exclusively marine that date from the Palaeozoic to the Early Mesozoic eras. Ever since their phosphatic parts, calcium phosphate or apatetic conodont “elements” were first described in 1856 by Pander their zoological relationships have been vigorously debated. An example is the listing of almost 50 publications (Müller, 1981) for the period 1856-1975 that suggested a variety of affinities with 10 different taxonomic entities, including such diverse groups as vertebrates, annelids and plants. Chinese terminology has 11 different words equivalent to higher taxa for conodonts (Wang Cheng-Yuan, pers. comm. to ST, 1984). Most relationships were easily dismissed (Sweet, 1988: 170-184), including strong evidence against any affinity with myxinoids (hagfishes), even questioning a relationship with chordates.  Sweet (1988: 172, 173) discussed the claim (Tillier & Cuif, 1986) though provided no refutation  to their claim that conodonts may be related to aplacophoran molluscs (but see Briggs et al., 1987), where they noted similarities between the 2, as they discovered calcium phosphate in the teeth and mandibles of one aplacophoran taxon. Calcium is also found in several “invertebrate” taxa such as in phyllocarids, the stylets of nemerteans, shells of some brachiopods, and is likely to also be found in the radula teeth of some chitons (Watabe, 1990), therefore the conclusions of Tillier & Cuif (1986) should, according to Turner & Burrow, be considered as being based on comparisons that are rather simplistic. The analysis by Sweet (1900) of possible affinities of the conodont organism led to him concluding that they could probably best be assigned to a separate phylum, and was the result of yet another evolutionary experiment that eventually went extinct.  In this paper Turner & Burrow continue the debate as they do not accept the increasingly prevailing paradigm that conodonts are vertebrates.

In this paper Turner & Burrow concentrate on only the euconodonts (= conodonts s.s.) or “complex” conodonts, as did (e.g. Donoghue & Aldridge, 2001, Donoghue et al., 2000, 2008), as well as others, who claim the conodonts are vertebrates, restricting their hypothesis of conodont interrelationships to euconodonts.


This paper was written as a further refutation of the hypothesis that conodonts are “stem gnathostomes” or vertebrates. According to Turner & Burrow conodonts are not recognised as a group of early vertebrates that had experimented with biomineralisation of their skeletons. Turner & Burrow suggest that conodonts might represent a cephalochordate grade of evolution at most, similar to the amphioxus Branchiostoma Contra, (e.g. Donoghue et al., Kuhn & Barnes, 2005; Janvier, 2008), the plesion Conodonta (Eichenberg, 1930), is in no way a sister group or a member, stem or otherwise of the phylum Craniata (Linnaeus, 1758), nor the superclass Gnathostomata (Cope, 1889). Turner & Burrow also say that the placing of higher taxa Conodontaphorida or Conodonta in the Chordata (Bateson, 1886) or Craniata (e.g. Farrell, 2004; Nelson, 2006; King et al., 2009) is not accepted for the reasons outlined above. Based on the evidence that is provided here, Turner & Burrow support the hypothesis that:

·         The phylogenetic status of conodonts s.l. that includes proto-, para- and euconodonts has not been resolved; at the present the 3 groups are informal, with proto-conodonts probably not being monophyletic. It is considered (Müller & Hinz-Schallreuter, 1998) that the 3 groups are related. The idea that protoconodonts that belong to the evolutionary lineage of Phakelodus is probably the stem group of chaetognaths is favoured by Szaniawski (2002). An evolutionary lineage that has been well documented from a paraconodont species to a euconodont species has been described (Szaniawski & Bengston, 1993). According to Turner & Burrow authors who relate euconodonts to craniates consider the 3 groups have different phylogenetic relationships;

·         Conodont elements are not odontodes and do not have vertebrate hard tissues, which includes globular cartilage, bone, lamellin, dentine, enameloid or enamel, and lack vertebrate morphogenesis; Turner & Burrow say that conodont elements that are broken could be repaired during the life of the animal and, therefore, the elements had to be infolded in tissue, at least at times, unlike odontodes, scales, teeth etc.

·         Conodont elements are not homologous with vertebrate teeth and do not represent the first vertebrate experiment in skeletonisation or feeding apparatus that are mineralised;

·         Conodont animals (euconodont) animals are not craniates, vertebrates nor “stem gnathostomes”.

Sources & Further reading

  1. Turner, S., C. J. Burrow, H.-P. Schultze, A. Blieck, W.-E. Reif, C. B. Rexroad, P. Bultynck and G. S. Nowlan (2010). "False teeth: conodont-vertebrate phylogenetic relationships revisited." Geodiversitas 32(4): 545-594.


Author: M. H. Monroe
Last updated  08/01/2016
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