[en] Equid evolution is characterized by a high diversity of extinct species and morphologies, whereas extant equids share a superficially similar, monodactyl morphology. This inferred musculoskeletal similarity of modern equid limbs remains unexplored, and it is often assumed that domestic horse limbs are representative for wild equids (e.g., zebras, onagers, etc.). Our aim was to quantitatively describe the muscle architecture and arrangement of all forelimb muscles in extant wild Equus species to test this assumption, and investigate any differences between the species. We hypothesized that there would be subtle variation linked to locomotion on the different substrates that these species encounter. Gross dissections were performed to record muscle attachment sites and to quantify architectural metrics: muscle-tendon unit (MTU) length, MTU mass, muscle mass, pennation angle, and fascicle length; physiological cross-sectional area (PCSA) of the muscles and tendon cross-sectional area (TCSA) of the distal ligaments were then calculated. Qualitative results confirm common origin and insertion sites of all muscles across all Equus species. When normalized for size, the forelimb muscles across equids generally exhibit comparable muscular architecture and force-generating capacities. However, we observed a trend for higher force-generating potential in the distal limb flexor muscles in two species of zebra naturally found in habitats with inclined or uneven substrates. Although limited by sample size, these results indicate that scaled data for modern wild equids are generally very comparable, which may enable much smoother translation of experimental data from domestic horses into digital simulations of wild equid locomotion, including for extinct equids.
De Ridder, Tim ; Department of Biology, Universiteit Antwerpen, Antwerp, Belgium
Aerts, Peter ; Department of Biology, Universiteit Antwerpen, Antwerp, Belgium ; Movement and Sports Sciences, University of Ghent, Ghent, Belgium
Maclaren, James ; Université de Liège - ULiège > Département de géologie > Evolution and diversity dynamics lab ; Department of Biology, Universiteit Antwerpen, Antwerp, Belgium ; Palaeobiosphere Evolution Lab, Institute of Natural Sciences, Brussels, Belgium
Language :
English
Title :
Could "wild horses" drag you away? Quantifying muscular architecture in the forelimbs of extant, non-domestic equids (Perissodactyla: Equidae).
Publication date :
2025
Journal title :
Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology
The authors wish to thank specific members of the Functional Morphology Lab: Jan Scholliers for building the insulated container for safe transport of frozen limb specimens from zoos to the university campus; Dr. Falk Mielke and Federico Banfi for assisting on collection trips; Dr. Sandra Nauwelaerts and Dr. Mari\u00EBlle Kaashoek for sourcing limbs of and from the GaiaZOO; Eleesha Annear for assisting in dissections, and Josie Meaney\u2010Ward for the bureaucratic assistance throughout data collection. We would also like to thank Prof. Dr. Chris Van Ginneken for access to the infrastructure and pathology lab at the Comparative Perinatal Development (CoPeD) Lab (Universiteit Antwerpen) for dissections, in addition to Ellen Goossenaerts, Marleen Cools, and Denise Vogel for facilitating and assisting in dissections and specimen storage. We thank George Hantke and Dr. Andrew Kitchener for providing us with an specimen and for hosting us at the National Museum of Scotland. We would like to extend thanks to the EAZA Equid Taxon Advisory Group (TAG), in addition to the staff of the institutions who donated specimens for this study: Tiergarten der Stadt N\u00FCrnberg; GaiaZoo; Zoological Gardens Karlsruhe; R\u00E9serve Africaine de Sigean; Parc Zoo du Reynou; Thoiry ZooSafari; Monde Sauvage; and to J\u2010P G\u00E9rard Simon S.A and their staff. This project was conducted as part of an FWO Junior Postdoctoral Fellowship awarded to JAM (Project ID: 12V8422N); several specimens were collected as part of a University of Antwerp Bijzonder Onderzoeksfonds (BOF\u2010UA) project awarded to PA (Project ID: DOC\u2010PRO 31518). Part of the manuscript writing was conducted during an FWO PhD Fellowship awarded to TDR (Project ID: 11D6025N) and FWO Senior Postdoctoral Fellowship awarded to JAM (Project ID: 12A0Y25N). Equus zebra E. f. przewalskii E. grevyi
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