Origins of mammalian vertebral function revealed through digital bending experiments

Area of Science:

• Paleontology
• Biomechanics
• Evolutionary Biology

Background:

• Understanding functional evolution in fossils is challenging.
• Computational modeling offers new ways to study extinct organism function.
• Non-mammalian synapsids are crucial for studying the mammal transition.

Purpose of the Study:

• To reconstruct vertebral function in non-mammalian synapsids.
• To investigate the functional basis of the synapsid-mammal transition.
• To compare vertebral mechanics across synapsids and extant tetrapods.

Main Methods:

• Digital bending experiments were used to estimate vertebral range of motion and joint stiffness.
• Eight non-mammalian synapsid species were analyzed.
• Comparative data from extant salamanders, reptiles, and mammals were included.

Main Results:

• Key mammalian vertebral functions evolved prior to crown Mammalia.
• Cynodonts stabilized their posterior trunks and developed anterior trunk axial rotation.
• Posterior sagittal bending in the trunk evolved later in mammals, potentially therians.

Conclusions:

• Vertebral function evolved incrementally, with significant steps occurring in non-mammalian ancestors.
• Functional diversification of the mammalian trunk involved co-option of existing regions.
• The evolution of the mammalian backbone involved multiple functional and evolutionary stages.