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Pelvic and reproductive structures in placoderms (stem gnathostomes).

Kate Trinajstic1, Catherine Boisvert, John Long

  • 1Department of Chemistry, Curtin University, Perth, Western Australia 6102, Australia; Earth and Planetary Sciences, Western Australian Museum, Perth, Western Australia 6000, Australia.

Biological Reviews of the Cambridge Philosophical Society
|June 4, 2014
PubMed
Summary
This summary is machine-generated.

Newly discovered pelvic and reproductive structures in placoderms challenge ideas about vertebrate evolution. These basal jawed vertebrates show claspers developing separately from pelvic fins, indicating complex reproductive strategies.

Keywords:
Devonianclasper organinternal fertilisationpelvic girdleplacodermviviparity

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Area of Science:

  • Paleontology
  • Vertebrate Anatomy
  • Evolutionary Biology

Background:

  • Placoderms are basal jawed vertebrates crucial for understanding gnathostome evolution.
  • Previous studies on placoderm pelvic structures and reproduction are re-examined.
  • The origin of pelvic girdles and reproductive complexity in vertebrates is debated.

Purpose of the Study:

  • To reinterpret pelvic and reproductive structures in arthrodire and ptyctodont placoderms.
  • To clarify the relationship between male claspers and pelvic girdles.
  • To understand the evolutionary development of reproductive strategies in early jawed vertebrates.

Main Methods:

  • Comparative morphological analysis of fossil placoderms (Arthrodira, Ptyctodontida).
  • Re-evaluation of existing descriptions of pelvic girdle and clasper morphology.
  • Analysis of fossil evidence for reproductive strategies, including multiple embryos.

Main Results:

  • Placoderm claspers and pelvic girdles appear to be separate structures, unlike in chondrichthyans.
  • Both pectoral and pelvic girdles, along with claspers, share dermal and perichondral components.
  • Placoderm claspers develop independently of pelvic fins, suggesting a distinct evolutionary pathway.
  • Fossil evidence indicates complex reproductive strategies in placoderms, including internal fertilization and development of multiple embryos.

Conclusions:

  • The independent development of claspers in placoderms suggests a novel evolutionary mechanism.
  • Placoderm reproductive strategies were more complex than previously assumed, comparable to some modern sharks.
  • These findings necessitate a revision of our understanding of pelvic girdle and reproductive organ evolution in jawed vertebrates.