Reverse-engineering the locomotion of a stem amniote

Area of Science:

• Paleontology
• Vertebrate Evolution
• Biomechanics

Background:

• Reconstructing extinct vertebrate locomotion is crucial for understanding palaeobiology and major evolutionary transitions.
• Estimating fossil locomotor behavior is challenging due to limited fossil evidence and the form-function disconnect.
• Advanced terrestrial locomotion is often linked to amniote diversification, but its origins in stem amniotes are unclear.

Purpose of the Study:

• To quantitatively reconstruct the gaits of the stem amniote Orobates pabsti using multiple methods.
• To determine if Orobates exhibited advanced locomotor characteristics previously associated with crown amniotes.
• To investigate the evolutionary timeline of advanced terrestrial locomotion relative to amniote diversification.

Main Methods:

• Utilized an integrative methodology combining biomechanically relevant metrics applicable to extant tetrapods.
• Employed in vivo locomotor mechanics assessment in four extant species to inform kinematic simulations of Orobates.
• Incorporated dynamic simulations and robotics to filter plausible gaits, validated with two extant species.

Main Results:

• Quantitative analysis indicates Orobates pabsti possessed more advanced locomotion than previously assumed for early tetrapods.
• The reconstructed gaits of Orobates align with its associated fossilized trackways.
• The findings suggest that advanced terrestrial locomotion predates the diversification of crown amniotes.

Conclusions:

• Orobates pabsti demonstrates that sophisticated terrestrial locomotion evolved earlier in vertebrate history than previously thought.
• Advanced terrestrial locomotion was not exclusive to early amniotes and likely originated in stem amniotes.
• This study provides a framework for future reconstructions of fossil locomotor behavior, allowing for methodological revisions.