J L Molnar1, J R Hutchinson2, R Diogo3, J A Clack4, S E Pierce5. 1. Anatomy Department, New York Institute of Technology College of Osteopathic Medicine, Northern Boulevard, Old Westbury, NY 11568, USA. julia.molnar@nyit.edu spierce@oeb.harvard.edu. 2. Structure & Motion Laboratory, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hertfordshire AL9 7TA, UK. 3. Anatomy Department, Howard University College of Medicine, 520 W St. NW, Numa Adams Building, Washington, DC 20059, USA. 4. University Museum of Zoology, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. 5. Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA. julia.molnar@nyit.edu spierce@oeb.harvard.edu.
Abstract
One of the most intriguing questions in vertebrate evolution is how tetrapods gained the ability to walk on land. Although many hypotheses have been proposed, few have been rigorously tested using the fossil record. Here, we build three-dimensional musculoskeletal models of the pectoral appendage in Eusthenopteron, Acanthostega, and Pederpes and quantitatively examine changes in forelimb function across the fin-to-limb transition. Through comparison with extant fishes and tetrapods, we show that early tetrapods share a suite of characters including restricted mobility in humerus long-axis rotation, increased muscular leverage for humeral retraction, but not depression/adduction, and increased mobility in elbow flexion-extension. We infer that the earliest steps in tetrapod forelimb evolution were related to limb-substrate interactions, whereas specializations for weight support appeared later. Together, these results suggest that competing selective pressures for aquatic and terrestrial environments produced a unique, ancestral "early tetrapod" forelimb locomotor mode unlike that of any extant animal.
One of the most intriguing questions in vertebrate evolution is how tetrapods gained the ability to walk on land. Although many hypotheses have been proposed, few have been rigorously tested using the fossil record. Here, we build three-dimensional musculoskeletal models of the pectoral appendage in Eusthenopteron, Acanthostega, and Pederpes and quantitatively examine changes in forelimb function across the fin-to-limb transition. Through comparison with extant fishes and tetrapods, we show that early tetrapods share a suite of characters including restricted mobility in humerus long-axis rotation, increased muscular leverage for humeral retraction, but not depression/adduction, and increased mobility in elbow flexion-extension. We infer that the earliest steps in tetrapod forelimb evolution were related to limb-substrate interactions, whereas specializations for weight support appeared later. Together, these results suggest that competing selective pressures for aquatic and terrestrial environments produced a unique, ancestral "early tetrapod" forelimb locomotor mode unlike that of any extant animal.
Authors: Stephen M Gatesy; Armita R Manafzadeh; Peter J Bishop; Morgan L Turner; Robert E Kambic; Andrew R Cuff; John R Hutchinson Journal: J Anat Date: 2022-02-03 Impact factor: 2.921