Relating neuromuscular control to functional anatomy of limb muscles in extant archosaurs

Journal Article · Fri Mar 08 00:00:00 EST 2019 · Journal of Morphology

DOI:https://doi.org/10.1002/jmor.20973· OSTI ID:1498590

Cuff, Andrew R.  ^[1]; Daley, Monica A. ^[1]; Michel, Krijn B. ^[1]; Allen, Vivian R. ^[1]; Lamas, Luis Pardon ^[1]; Adami, Chiara ^[2]; Monticelli, Paolo ^[2]; Pelligand, Ludo ^[2]; Hutchinson, John R.  ^[1]

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1. Structure and Motion Laboratory, Department of Comparative Biomedical Sciences Royal Veterinary College Hawkshead Lane, North Mymms, Hertfordshire, AL9 7TA United Kingdom
2. Queen Mother Hospital, Department of Clinical Science and Services Royal Veterinary College Hawkshead Lane, North Mymms, Hertfordshire United Kingdom

Abstract Electromyography (EMG) is used to understand muscle activity patterns in animals. Understanding how much variation exists in muscle activity patterns in homologous muscles across animal clades during similar behaviours is important for evaluating the evolution of muscle functions and neuromuscular control. We compared muscle activity across a range of archosaurian species and appendicular muscles, including how these EMG patterns varied across ontogeny and phylogeny, to reconstruct the evolutionary history of archosaurian muscle activation during locomotion. EMG electrodes were implanted into the muscles of turkeys, pheasants, quail, guineafowl, emus (three age classes), tinamous and juvenile Nile crocodiles across 13 different appendicular muscles. Subjects walked and ran at a range of speeds both overground and on treadmills during EMG recordings. Anatomically similar muscles such as the lateral gastrocnemius exhibited similar EMG patterns at similar relative speeds across all birds. In the crocodiles, the EMG signals closely matched previously published data for alligators. The timing of lateral gastrocnemius activation was relatively later within a stride cycle for crocodiles compared to birds. This difference may relate to the coordinated knee extension and ankle plantarflexion timing across the swing‐stance transition in Crocodylia, unlike in birds where there is knee flexion and ankle dorsiflexion across swing‐stance. No significant effects were found across the species for ontogeny, or between treadmill and overground locomotion. Our findings strengthen the inference that some muscle EMG patterns remained conservative throughout Archosauria: for example, digital flexors retained similar stance phase activity and M. pectoralis remained an ‘anti‐gravity’ muscle. However, some avian hindlimb muscles evolved divergent activations in tandem with functional changes such as bipedalism and more crouched postures, especially M. iliotrochantericus caudalis switching from swing to stance phase activity and M. iliofibularis adding a novel stance phase burst of activity.

• Sponsoring Organization: USDOE
• OSTI ID: 1498590
• Journal Information: Journal of Morphology, Journal Name: Journal of Morphology Vol. 280 Journal Issue: 5; ISSN 0362-2525
• Publisher: Wiley Blackwell (John Wiley & Sons)
• Country of Publication: United States
• Language: English