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Vertebral architecture in the earliest stem tetrapods
Stephanie E Pierce1, Per E Ahlberg, John R Hutchinson
1University Museum of Zoology, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. spierce@rvc.ac.uk
Nature
|January 22, 2013
Summary
Early tetrapod vertebral evolution is revised. The study reveals a
Area of Science:
- Paleontology
- Vertebrate Anatomy
- Evolutionary Biology
Background:
- Vertebral column construction is key to diagnosing early tetrapod groups.
- Rhachitomous vertebrae are traditionally considered ancestral for tetrapods.
- Limited knowledge exists on earliest stem tetrapod vertebral anatomy due to preservation issues.
Purpose of the Study:
- To describe the 3D vertebral architecture of the stem tetrapod Ichthyostega.
- To investigate vertebral anatomy in early tetrapods using advanced imaging.
- To revise understanding of vertebral column evolution in early tetrapods.
Main Methods:
- Utilized propagation phase-contrast X-ray synchrotron microtomography.
- Analyzed the vertebral architecture of Ichthyostega.
- Compared vertebral morphology with Acanthostega and Pederpes.
Main Results:
- Revealed diverse new morphological, developmental, and functional characteristics.
- Identified a 'reverse' rhachitomous vertebral design in Ichthyostega, with fused pleurocentra and intercentra.
- Observed a possible posterior-to-anterior vertebral ossification sequence and the first ossified sternal elements.
Conclusions:
- The 'reverse' rhachitomous vertebral design may be the ancestral condition for limbed vertebrates.
- This finding fundamentally revises current understanding of early tetrapod vertebral evolution.
- Raises questions about presumed vertebral architecture in tetrapodomorph fish and crownward tetrapods.
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