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Royal Society open science2023; 10(6); 230358; doi: 10.1098/rsos.230358

Hipparion tracks and horses’ toes: the evolution of the equid single hoof.

Abstract: The traditional story of the evolution of the horse (family Equidae) has been in large part about the evolution of their feet. How did modern horses come to have a single toe (digit III), with the hoof bearing a characteristic V-shaped keratinous frog on the sole, and what happened to the other digits? While it has long been known that the proximal portions of digits II and IV are retained as the splint bones, a recent hypothesis suggested that the distal portion of these digits have also been retained as part of the frog, drawing upon the famous Laetoli footprints of the tridactyl (three-toed) equid as part of the evidence. We show here that, while there is good anatomical and embryological evidence for the proximal portions of all the accessory digits (i.e. I and V, as well as II and IV) being retained in the feet of modern horses, evidence is lacking for the retention of any distal portions of these digits. There is also good ichnological evidence that many tridactyl equids possessed a frog, and that the frog has been part of the equid foot for much of equid evolutionary history.
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Publication Date: 2023-06-21 PubMed ID: 37351494PubMed Central: PMC10282582DOI: 10.1098/rsos.230358Google Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article discusses the evolution of the horse’s foot, mainly focusing on how the modern horse has transitioned to a single-toe structure, with a characteristic V-shaped keratinous frog part on the sole, from a three-toe structure. The researchers further investigate an hypothesis suggesting that the remains of the distal portions of the vanished digits form part of the frog.

Introduction

  • The research provides a detailed insight into the evolution of the horse’s foot, coming from the family Equidae.
  • It mainly focuses on how horses have evolved from having three toes (digits II, III, and IV) to just one toe (digit III) with a unique V-shaped keratinous component on the sole known as the ‘frog’.
  • Then, it conducts a deep dive into an hypothesis that suggests that the frog on a horse’s foot could contain remnants of the distal portions of the lost digits.

The Evolution of the Horse Foot

  • The researchers indicate that horse’s fee evolution has traditionally been a major fascination in the realm of biological and evolutionary research.
  • They focus on how modern horses, instead of having three separate toes like their ancestors, now possess a single toe (digit III).
  • A probing question is what happened to the missing digits. It has been established that the proximal parts of the absent digits are retained as splint bones.

The Hypothesis on Digit Retainment

  • The researchers examine a recent hypothesis suggesting that not only the proximal parts, but also the distal parts of the disappeared digits might be retained as a part of the frog.
  • To back up this hypothesis, they refer to the renowned Laetoli footprints of the tridactyl (three-toed) equine species.

The Findings

  • The researchers find compelling anatomical and embryological evidence supporting the retainment of the proximal parts of all the accessory digits (i.e. I and V, as well as II and IV) in the feet of modern horses.
  • The evidence regarding the distal retainment of these discontinued digits in the form of the ‘frog’ is, however, inadequate.
  • They also establish that many three-toed equines had a frog, implying that the frog has been a part of the equine foot throughout most of its evolutionary history.

Cite This Article

APA
Vincelette AR, Renders E, Scott KM, Falkingham PL, Janis CM. (2023). Hipparion tracks and horses’ toes: the evolution of the equid single hoof. R Soc Open Sci, 10(6), 230358. https://doi.org/10.1098/rsos.230358

Publication

Royal Society open science
ISSN: 2054-5703
NlmUniqueID: 101647528
Country: England
Language: English
Volume: 10
Issue: 6
Pages: 230358
PII: 230358

Researcher Affiliations

Vincelette, Alan R
  • Department of Pathology, St. John's Seminary, Camarillo, 93012, CA, USA.
Renders, Elise
  • Department of Functional Morphology, Faculty of Veterinary Medicine, Utrecht University (Ret.), Utrecht, 3584 CM, The Netherlands.
Scott, Kathleen M
  • Department of Cell Biology and Neuroscience, Rutgers University, New Brunswick, 08854, NJ, USA.
Falkingham, Peter L
  • School of Biological and Environmental Sciences, Liverpool John Moores University, Liverpool, L3 3AF, UK.
Janis, Christine M
  • Bristol Palaeobiology Group, School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK.
  • Department of Ecology and Evolutionary Biology, Brown University, Providence, 02912, RI, USA.

Conflict of Interest Statement

We declare we have no competing interests.

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Citations

This article has been cited 2 times.
  1. Vincelette A. The Characteristics, Distribution, Function, and Origin of Alternative Lateral Horse Gaits. Animals (Basel) 2023 Aug 8;13(16).
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  2. Lovász L, Sommer-Trembo C, Barth JMI, Scasta JD, Grancharova-Hill R, Lemoine RT, Kerekes V, Merckling L, Bouskila A, Svenning JC, Fages A. Rewilded horses in European nature conservation - a genetics, ethics, and welfare perspective. Biol Rev Camb Philos Soc 2025 Feb;100(1):407-427.
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