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Quantifying Evolutionary Dynamics of Arthropodization and Arthrodization
Cong Liu1, Yu Wu1, Dongjing Fu1
1State Key Laboratory of Continental Evolution and Early Life, Shaanxi Key Laboratory of Early Life and Environments, Department of Geology, Northwest University, Xi'an, China.
Summary
Arthrodization and arthropodization, key euarthropod features, evolved convergently and modularly across Ecdysozoa. These traits show repeated gains and losses, not a simple progressive sequence.
Area of Science:
- Evolutionary Biology
- Developmental Biology
- Paleontology
Background:
- Euarthropods exhibit segmented, sclerotized, and articulated bodies and appendages via arthrodization and arthropodization.
- These features are considered defining for Euarthropoda, with a proposed sequential evolution: arthropodization preceding arthrodization, initially in frontal appendages.
Purpose of the Study:
- To investigate the evolutionary patterns of arthrodization and arthropodization across Ecdysozoa.
- To test the hypothesis of a specific, progressive evolutionary sequence for these key euarthropod traits.
Main Methods:
- Morphological comparisons across Ecdysozoa.
- Ancestral-state reconstruction (ASR) to infer trait evolution.
- Semi-quantitative methods to assess degrees of arthrodization and arthropodization.
Main Results:
- ASR and morphological data reveal recurrent gains, losses, and regional decoupling of segmentation, sclerotization, and articulation.
- Variable degrees of arthrodization and arthropodization were observed across ecdysozoan lineages.
- No progressive increase in these traits was found from basal to crown-group euarthropods.
Conclusions:
- Arthrodization and arthropodization evolved in a modular and convergent manner across different ecdysozoan lineages.
- Evolution likely involved repeated modification, reduction, or redeployment of ancestral developmental toolkits, rather than a strict sequential process.
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