Adaptive landscapes unveil the complex evolutionary path from sprawling to upright forelimb function and posture in
Robert J Brocklehurst1, Magdalen Mercado1,2, Kenneth D Angielczyk2,3
1Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America.
Plos Biology
|June 24, 2025
Summary
Mammalian evolution involved a sprawling-parasagittal posture transition. Fossil synapsid forelimb function reveals posture was evolutionarily labile, not a direct progression to parasagittal mammals.
Area of Science:
- Paleontology
- Evolutionary Biology
- Biomechanics
Background:
- The sprawling-parasagittal posture transition is crucial to mammalian evolution.
- Fossil synapsid forelimb function is debated, complicating understanding of this transition.
Purpose of the Study:
- To investigate the origins of mammalian posture using evolutionary adaptive landscapes.
- To integrate 3D humerus shape and functional performance data in synapsids.
Main Methods:
- Utilized evolutionary adaptive landscapes.
- Integrated 3D humerus shape and functional performance data.
- Analyzed a comprehensive sample of fossil synapsids and extant comparators.
Main Results:
- Early synapsids exhibited a sprawling posture intermediate between reptiles and monotremes.
- Synapsid humerus evolution showed limited direct progression from sprawling to parasagittal forms.
- Posture was evolutionarily labile, varying with ecological diversification.
Conclusions:
- Synapsids frequently evolved toward parasagittal postures, diverging from optimal paths.
- Habitual parasagittal postures first appeared in stem therians.
- Synapsids historically radiated with diverse forelimb trait combinations.
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