Historical perspectives on the evolution of tetrapodomorph movement

Area of Science:

• Paleontology
• Vertebrate Evolution
• Biomechanics

Background:

• Modern analogs are crucial for understanding extinct animal locomotion.
• Previous studies on early tetrapod locomotion have had mixed success.
• A phylogenetic review of analogs from chondrichthyans to mammals is needed.

Purpose of the Study:

• To review modern analogs used for inferring locomotor performance in stem tetrapods.
• To discuss the advantages and disadvantages of using modern analogs for water-to-land transition studies.
• To propose a "total-evidence" approach for reconstructing extinct locomotion.

Main Methods:

• Phylogenetic review of modern vertebrate analogs.
• Analysis of locomotor behaviors across diverse vertebrate clades.
• Comparative anatomy of limb joint morphology in extinct and extant taxa.
• Evaluation of fossil evidence alongside living animal data.

Main Results:

• Modern analogs offer a broad spectrum of locomotor behaviors but have limitations for early tetrapod studies.
• A "total-evidence" approach, focusing on constraints, is recommended over functional specifics.
• Ichthyostega likely could not perform modern quadrupedal locomotion but may have used mudskipper-like "crutching" motions.
• Other Devonian stem tetrapods likely possessed similar limb joint mobility to Ichthyostega.

Conclusions:

• Reconstructing extinct locomotion requires integrating fossil evidence with data from living animals.
• The "total-evidence" approach provides a more robust framework for understanding evolutionary transitions.
• Mudskipper-like locomotion is a plausible model for Ichthyostega's limb function.
• Limb joint morphology suggests similar locomotor capabilities among known Devonian stem tetrapods.