Conodont anatomy, chordate phylogeny and vertebrate classification

  title={Conodont anatomy, chordate phylogeny and vertebrate classification},
  author={Philip C. J. Donoghue and Mark A. Purnell and Richard J. Aldridge},
Interpretations of conodont anatomy and affinity continue to generate controversy. Fossilized soft-tissue evidence indicates that conodonts possessed eyes, extrinsic eye muscles, a notochord, myomeres, a differentiated tail with fin radiais, possible otic capsules and possible branchial structures. Indirect evidence suggests a differentiated brain and cartilaginous head skeleton. The multi-component phosphatic tissue complexes of the conodont feeding apparatus cannot be compared to the… 

Tables from this paper

False teeth: conodont-vertebrate phylogenetic relationships revisited
An evidence-based reassessment of the phylogenetic relationships of conodonts shows that they are not “stem” gnathostomes, nor vertebrates, and not even craniates, which supports neither a vertebrate nor a craniate relationship for conodons.
The origin of conodonts and of vertebrate mineralized skeletons
The hypothesis that teeth evolved before jaws and the inside-out hypothesis of dental evolution must be rejected; teeth seem to have evolved through the extension of odontogenic competence from the external dermis to internal epithelium soon after the origin of jaws.
Growth and feeding ecology of coniform conodonts
Conodonts were the first vertebrates to develop mineralized dental tools, known as elements. Recent research suggests that conodonts were macrophagous predators and/or scavengers but we do not know
Morphometric analysis of taxonomy, evolution, autecology and homology in ozarkodinid conodonts
This study has quantified evolutionary rates in conodonts for the first time and the methods and results presented here have the potential to catalyse comprehensive morphometric analysis of conodons using these widely applicable protocols.
The hypothesis that conodonts are vertebrates rests solely on evidence of soft tissue anatomy, and it is found that the range of microstructural variation observed hitherto was already apparent among plesiomorphic euconodronts.
Growth allometry and dental topography in Upper Triassic conodonts supports trophic differentiation and molar-like element function
The results indicate that Late Triassic species occupied the predator/scavenger niche in spite of the highly developed diversity of gnathostomes in this niche, and supports trophic diversification as an important driver of the remarkable disparity of their elements.
A critical reappraisal of the fossil record of the bilaterian phyla.
It is shown that the prospect of lineage diversification occurring early in the Proterozoic can be seen to be unlikely on grounds of both parsimony and functional morphology, and this analysis points to the requirement for a careful application of systematic methodology before explanations are sought for alleged patterns of constraint and flexibility.
Directional evolution in the conodont Pterospathodus
  • David Jones
  • Geography, Environmental Science
  • 2009
Standardized morphometric protocols are applied to skeletal elements belonging to the conodont Pterospathodus, derived from a densely sampled section from Estonia, establishing a robust quantitative framework for morphological variation in Pterodonts and suggesting that allometric repatterning was the proximal mechanism responsible for mediating the observed shifts in morphology through time.
The new head hypothesis revisited.
When the origin of neural crest and neurogenic placodes is examined within the context of developmental biology, it appears they evolved due to the rearrangement of germ layers in the blastulae of the deuterostomes that gave rise to chordates.


Soft anatomy and the affinities of conodonts
The available soft tissue evidence suggests that conodonts are best regarded as the sister group of the craniates.
The anatomy of conodonts
Ten specimens from the Carboniferous Granton shrimp bed of Edinburgh, Scotland, provide the most complete record of conodont anatomy, with evidence of incomplete preservation of ventral soft parts, at least at the anterior end of the specimens.
Decay of Branchiostoma: implications for soft‐tissue preservation in conodonts and other primitive chordates
Decay experiments on the cephalochordate Branchiostoma lanceolatum (‘amphioxus’) demonstrate that the most decay resistant structures are the notochord sheath and the cartilaginous rods which support the gill bars, and cast light on the interpretation of a number of primitive fossil chordates.
The conodont animal
A unique specimen of a small, elongate, soft-bodied animal from the Lower Carboniferous of the Edinburgh district, Scotland, is described. The head expands anteriorly into two lobate structures
The structure of some Middle Cambrian conodonts, and the early evolution of conodont structure and function
A proposed model of the early evolution of conodonts involves that elements of the Conodontiformes were completely engulfed in epithelial pockets, which enabled them to grow holoperipherally and thus to assume more complex shapes that could be retained during growth.
The conodont controversies.
The Origin and Early Evolution of the Craniata
The origin of the Craniata, one of the three subphyla of the Phylum Chordata, has generated more controversy in terms of numbers of likely ancestors than the origin of any other metazoan group.
The phylogeny of the Craniata, with particular reference to the significance of fossil “agnathans”
It is concluded that the fossil jawless Craniata provide little information on the affinities of the CraniATA, but they do provide complementary data on distribution of characters.
Architecture and functional morphology of the skeletal apparatus of ozarkodinid conodonts
According to this hypothesis, the anterior part of the conodont apparatus is comparable to, and possibly homologous with, the lingual apparatus of extant agnathans; the elements themselves have no direct homologues.
Ontogeny of the head of the Pacific hagfish (Eptatretus stouti, Myxinoidea): development of the lateral line system.
  • H. Wicht, R. Northcutt
  • Biology
    Philosophical transactions of the Royal Society of London. Series B, Biological sciences
  • 1995
It is found that an embryonic lateral line system is present in hagfishes, and that the grooves of adult hagFishes in all probability derive from lateral line placodes, which is a primitive character of craniates.