Histology and affinity of anaspids, and the early evolution of the vertebrate dermal skeleton

Joseph N Keating*, Philip C J Donoghue

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

20 Citations (Scopus)
267 Downloads (Pure)

Abstract

The assembly of the gnathostome bodyplan constitutes a formative episode in vertebrate evolutionary history, an interval in which the mineralised skeleton and its canonical suite of cell and tissue types originated. Fossil jawless fishes, assigned to the gnathostome stem-lineage, provide an unparalleled insight into the origin and evolution of the skeleton, hindered only by uncertainty over the phylogenetic position and evolutionary significance of key clades. Chief among these are the jawless anaspids, whose skeletal composition, a rich source of phylogenetic information, is poorly characterised. Here we survey the histology of representatives spanning anaspid diversity and infer their generalised skeletal architecture. The anaspid dermal skeleton is composed of odontodes comprising spheritic dentine and enameloid, overlying a basal layer of acellular parallel fibre bone containing an extensive shallow canal network. A recoded and revised phylogenetic analysis using equal and implied weights parsimony resolves anaspids as monophyletic, nested among stem-gnathostomes. Our results suggest the anaspid dermal skeleton is a degenerate derivative of a histologically more complex ancestral vertebrate skeleton, rather than reflecting primitive simplicity. Hypotheses that anaspids are ancestral skeletonising lampreys, or a derived lineage of jawless vertebrates with paired fins, are rejected.
Original languageEnglish
Article number20152917
Number of pages10
JournalProceedings of the Royal Society B: Biological Sciences
Volume283
Issue number1826
Early online date9 Mar 2016
DOIs
Publication statusPublished - Mar 2016

Keywords

  • histology
  • anaspid
  • gnathostome
  • skeleton
  • dermal
  • odontode

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