People enjoy looking back at videos that show them taking their first steps. There’s a natural fascination with watching ourselves navigate obstacles for the first time, attempting to support our weight by grabbing tables and our parents’ legs. Stumbling around is part of a long tradition going back millions of years to when early four limbed creatures, the tetrapods, first made it on to land. Obviously, there’s no way to watch footage of these first steps, but by studying the locomotion of modern tetrapods, we may be able to predict how our ancestors first crawled out of the water. A team of scientists lead by Dr. Stephanie Pierce of Harvard University contributed to this effort to understand the evolution of tetrapod locomotion with a study on the beautiful fire salamander.
A very charismatic fire salamander in its natural habitat. (Photo by William Warby).
The fire salamander is a natural choice of study given the history of using salamanders and relatives as a model for the evolution of tetrapod locomotion. By inserting electrodes into the salamanders’ muscles, the researchers were able to measure muscle activity as the organisms walked. Prior electromyography (EMG) studies have used the tiger salamander, giant coastal salamander, and newts. This study stands out in not just its novel choice of organism, but also in measuring forelimb, hindlimb, and axial musculature activity, rather than just one or two of those. By providing a more comprehensive understanding of the Fire Salamanders’ movement, the data allows for comparison across a broader range of studies.
Results from this study demonstrate which muscles are active during each stage of steady state walking. It turns out that Fire Salamander kinematics are fairly similar to previously studied relatives, but not identical. The cause behind the unique aspects, the activity of specific muscles during stance-to-swing transition, lack of a burst of activity noted in other species, and more, is currently unknown and is a promising area of future research. The results also support previous findings that suggest that hindlimb kinematics is conserved across terrestrial tetrapods, particularly their ventral muscles. Forelimb kinematics do also share some similarity across clades and some variation was likely due to experimental methods. Overall, this study shows there are conserved elements of locomotory neuromusculature, potentially indicating inheritance from a common ancestor. Thus, this study paves the way for studying extinct animals through simulations of musculoskeletal models reconstructed from fossil data.