Early Jawless Vertebrates and Cyclostome Origins

@inproceedings{Janvier2008EarlyJV,
  title={Early Jawless Vertebrates and Cyclostome Origins},
  author={Philippe Janvier},
  booktitle={Zoological science},
  year={2008}
}
  • P. Janvier
  • Published in Zoological science 2008
  • Biology, Medicine
Abstract Undoubted fossil lampreys are recorded since the Late Devonian (358 Ma), and probable fossil hagfishes since the Late Carboniferous (300 Ma), but molecular clock data suggest a much earlier divergence times for the two groups. In the early 20th century, hagfishes and lampreys were generally thought to have diverged much later from unknown ancestral cyclostomes, in turn derived through ‘degeneracy’ from some Paleozoic armored jawless vertebrates, or ‘ostracoderms.’ However, current… Expand
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Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological–molecular conflict in early vertebrate phylogeny
TLDR
By addressing nonindependence of characters, phylogenetic analyses recovered hagfish and lampreys in a clade of cyclostomes (congruent with the cyclostome hypothesis) using only morphological data, which potentially resolve the morphological–molecular conflict at the base of the Vertebrata. Expand
Evo-devo studies of cyclostomes and the origin and evolution of jawed vertebrates.
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  • Medicine
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The transition from jawless to jawed vertebrates was thus driven by heterotopy of development, mainly caused by separation and shift of ectodermal placodes and resultant ectomesenchymal distribution, and shifts of the epithelial-mesenchyal interactions that underlie craniofacial differentiation. Expand
Craniofacial development of hagfishes and the evolution of vertebrates
TLDR
The craniofacial development of a series of staged hagfish embryos is described, which shows that their adenohypophysis arises ectodermally, consistent with the molecular phylogenetic data and identifies a pan-cyclostome pattern, one not shared by jawed vertebrates. Expand
Using information in taxonomists’ heads to resolve hagfish and lamprey relationships and recapitulate craniate–vertebrate phylogenetic history
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This reanalysis emphasises that the debate on whether the Cyclostomata is monophyletic or paraphyletic must be resolved formally on the basis of principles and practices for phylogenetic systematic analysis including fossil data. Expand
Cranium, Cephalic Muscles, and Homologies in Cyclostomes
TLDR
Comparative anatomical and evolutionary developmental studies help to reconstruct the last common ancestor of vertebrates, cyclostomes, and gnathostomes and provide insights into the evolution of the jaws and associated muscles. Expand
The evolution of lamprey (Petromyzontida) life history and the origin of metamorphosis
TLDR
A review synthesizes findings and concludes that the ancestral lamprey life cycle followed a direct development, suggesting that the larval period was short and relatively limited if present at all, but that the juvenile included modern larval traits. Expand
microRNAs revive old views about jawless vertebrate divergence and evolution
  • P. Janvier
  • Biology, Medicine
  • Proceedings of the National Academy of Sciences
  • 2010
TLDR
Two small fish groups, hagfishes and lampreys, are devoid of jaws and are either ignored by the public or regarded as pests, so these fishes became finally considered in evolutionary times as a monophyletic offshoot of primitive vertebrates, sister group to jawed vertebrates. Expand
Discovery of fossil lamprey larva from the Lower Cretaceous reveals its three-phased life cycle
TLDR
The discovery of exceptionally preserved premetamorphic and metamorphosing larvae of the fossil lamprey Mesomyzon mengae from the Lower Cretaceous of Inner Mongolia, China are reported, indicating the three-phased life cycle in lampreys emerged essentially in their present mode no later than the Early Cret Jurassic. Expand
Palaeospondylus as a primitive hagfish
TLDR
The first comparative morphological analysis of hagfish embryos and Palaeospondylus is reported, and a hitherto overlooked resemblance in the chondrocranial elements of these animals is reported; i.e., congruence in the arrangement of the nasal capsule, neurocranium and mandibular arch-derived velar bar. Expand
Genome biology of the cyclostomes and insights into the evolutionary biology of vertebrate genomes.
TLDR
The deep shared ancestry and rapid divergence of lampreys, hagfish and gnathostomes is considered evidence that the two versions of programmed rearrangement present in lamprey and hag fish were present in an ancestral lineage that existed more than 400 million years ago and perhaps included the ancestor of the jawed vertebrates. Expand
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