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Early tetrapod cranial evolution is characterized by increased complexity, constraint, and an offset from fin-limb

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Area of Science:

  • Paleontology
  • Evolutionary Biology
  • Comparative Anatomy

Background:

  • The evolution of the tetrapod body plan is well-studied, particularly limb modifications.
  • However, the evolutionary history and cranial changes during the tetrapod origin remain less understood.
  • Skull bone reduction is hypothesized to drive vertebrate diversification, but its role in early tetrapods is unclear.

Purpose of the Study:

  • To investigate the impact of skull bone reduction on cranial evolution during the tetrapod origin.
  • To quantify topological changes in cranial anatomy across the fin-to-limb transition.

Main Methods:

  • Utilized anatomical network analysis to quantify topological changes in cranial anatomy.
  • Examined fossil and extant taxa spanning the fin-to-limb transition.

Main Results:

  • Observed an association between bone loss in the tetrapod skull and increased complexity of bone-to-bone contacts.
  • Documented a decrease in topological diversity of cranial anatomy during the late Paleozoic.
  • Identified a 10-million-year offset between the evolutionary timing of limb and cranial morphology.

Conclusions:

  • Skull bone loss during tetrapod origins may be influenced by developmental and/or mechanical constraints.
  • Cranial and limb evolution were driven by different factors and occurred asynchronously during the early tetrapod diversification.