Turner, ML, Falkingham, PL and Gatesy, SM (2022) What is Stance Phase On Deformable Substrates? Integrative and Comparative Biology. ISSN 1540-7063

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Abstract

The stance phase of walking is when forces are applied to the environment to support, propel, and maneuver the body. Unlike solid surfaces, deformable substrates yield under load, allowing the foot to sink to varying degrees. For bipedal birds and their dinosaurian ancestors, a shared response to walking on these substrates has been identified in the looping path the digits follow underground. Because a volume of substrate preserves a 3-D record of stance phase in the form of footprints or tracks, understanding how the bipedal stride cycle relates to this looping motion is critical for building a track-based framework for the study of walking in extinct taxa. Here, we used biplanar X-ray imaging to record and analyze 161 stance phases from 81 trials of three Helmeted Guineafowl (Numida meleagris) walking on radiolucent substrates of different consistency (solid, dry granular, and firm to semi-liquid muds). Across all substrates, the feet sank to a range of depths up to 78% of hip height. With increasing substrate hydration, the majority of foot motion shifted from above to below ground. Walking kinematics sampled across all stride cycles revealed six sequential gait-based events originating from both feet, conserved throughout the spectrum of substrate consistencies during normal alternating walking. On all substrates that yielded, five sub-phases of stance phase were drawn out in space and formed a loop of varying shape. We describe the two-footed coordination and weight distribution that likely contributed to the observed looping patterns of an individual foot. Given such complex subsurface foot motion during normal alternating walking and some atypical walking behaviors, we discuss the definition of “stance phase” on deformable substrates. We also discuss implications of the gait-based origins of subsurface looping on the interpretation of locomotory information preserved in fossil dinosaur tracks.

Item Type:	Article
Additional Information:	This is a pre-copyedited, author-produced version of an article accepted for publication in Integrative and Comparative Biology following peer review. The version of record Morgan L Turner, Peter L Falkingham, Stephen M Gatesy, What is Stance Phase on Deformable Substrates?, Integrative and Comparative Biology, 2022;, icac009 is available online at: https://doi.org/10.1093/icb/icac009
Uncontrolled Keywords:	0601 Biochemistry and Cell Biology, 0602 Ecology, 0608 Zoology
Subjects:	Q Science > QD Chemistry Q Science > QH Natural history > QH301 Biology Q Science > QL Zoology Q Science > QR Microbiology Q Science > QE Geology > QE701 Paleontology
Divisions:	Biological & Environmental Sciences (from Sep 19)
Publisher:	Oxford University Press (OUP)
Date Deposited:	08 Apr 2022 09:48
Last Modified:	23 Mar 2023 00:50
DOI or ID number:	10.1093/icb/icac009
URI:	https://researchonline.ljmu.ac.uk/id/eprint/16593

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