Early amphibians evolved distinct vertebrae for habitat invasions

Area of Science:

• Paleontology
• Vertebrate Evolution
• Functional Morphology

Background:

• The transition of tetrapods to land ~360-340 million years ago is pivotal for vertebrate evolution.
• Understanding vertebral form's role in locomotion across terrestrial and aquatic environments in early tetrapods remains unclear.
• Previous studies lacked systematic analysis of vertebral shape correlating with habitat and locomotion.

Purpose of the Study:

• To quantify vertebral shape diversity in Paleozoic amphibians (Temnospondyli).
• To investigate correlations between vertebral morphology, habitat (terrestrial vs. aquatic), and locomotion.
• To test hypotheses regarding vertebral function, particularly weight-bearing versus muscle attachment.

Main Methods:

• Geometric morphometrics applied to quantify vertebral shape across a diverse range of Temnospondyli.
• Comparative analysis of vertebral morphology in relation to inferred paleoenvironments.
• Examination of neural arch and intercentra features for functional and ecological insights.

Main Results:

• Temnospondyli exhibited greater vertebral shape diversity than previously recognized.
• Evidence suggests Temnospondyli were ancestrally terrestrial with multiple aquatic re-invasions.
• Intercentra shape, not neural arch features, strongly correlated with habitat, showing convergent evolution in terrestrial and aquatic forms.

Conclusions:

• Vertebral intercentra morphology is a critical indicator of habitat preference and locomotion in early tetrapods.
• Neural arch features related to muscle attachment were more plastic than previously assumed across the water-land transition.
• This study reveals morphological constraints on locomotion imposed by vertebrae, independent of phylogenetic history.