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Proceedings. Biological sciences2016; 283(1829); doi: 10.1098/rspb.2015.2947

New insights on equid locomotor evolution from the lumbar region of fossil horses.

Abstract: The specialization of equid limbs for cursoriality is a classic case of adaptive evolution, but the role of the axial skeleton in this famous transition is not well understood. Extant horses are extremely fast and efficient runners, which use a stiff-backed gallop with reduced bending of the lumbar region relative to other mammals. This study tests the hypothesis that stiff-backed running in horses evolved in response to evolutionary increases in body size by examining lumbar joint shape from a broad sample of fossil equids in a phylogenetic context. Lumbar joint shape scaling suggests that stability of the lumbar region does correlate with size through equid evolution. However, scaling effects were dampened in the posterior lumbar region, near the sacrum, which suggests strong selection for sagittal mobility in association with locomotor-respiratory coupling near the lumbosacral joint. I hypothesize that small-bodied fossil horses may have used a speed-dependent running gait, switching between stiff-backed and flex-backed galloping as speed increased.
© 2016 The Author(s).
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Publication Date: 2016-04-29 PubMed ID: 27122554PubMed Central: PMC4855377DOI: 10.1098/rspb.2015.2947Google Scholar: Lookup
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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.

This research article explores the evolution of the running biomechanics of horses, specifically focusing on the role of the lumbar region (lower back) in developing their efficient and fast gallop. The researcher hypothesizes that the stiff-backed running style of modern horses, a characteristic resulting in higher running speeds, evolved in response to increases in body size over time, and this is tested with the help of fossil evidences.

Objective of the Study

  • The study aims to understand the evolution of locomotion in horses, particularly focusing on the lumbar region’s role, which remains understudied within this context.
  • By examining the shape of the lumbar joint in a wide range of fossil equids (ancient horses), the research attempts to test the hypothesis that the stiffness and efficiency of horses’ gallop evolved as a response to an increase in body size throughout evolution.

Hypothesis and Methodology

  • The primary hypothesis is that small-bodied ancient horses may have adopted multiple gaits during running, including a speed-dependent switch between a stiff-backed and a flex-backed gallop.
  • The researcher scrutinizes the lumbar joint’s shape from a wide sample of fossil equids within a phylogenetic context to investigate this theory.

Main Findings

  • The analysis suggests that the stability of the lumbar region does correlate with size throughout equid evolution, supporting the hypothesis that the stiff-backed running style of horses has evolved in response to increases in body size.
  • The effects of size scaling, however, were found to be reduced near the sacrum in the posterior lumbar region. This hints towards a strong selection pressure for sagittal (front-to-back) mobility in connection with locomotor-respiratory coupling near the lumbosacral joint (where lumbar spine meets the sacrum).

Implications of the Study

  • This research provides new insights into the well-known adaptive transition of horsepower, especially focusing on the critical, but often overlooked, role of the axial skeleton.’
  • The findings could help understand the biomechanics of not only horses but possibly other cursorial animals (adapted for running), and may prove beneficial in the world of veterinary medicine or animal athletic training.

Cite This Article

APA
Jones KE. (2016). New insights on equid locomotor evolution from the lumbar region of fossil horses. Proc Biol Sci, 283(1829). https://doi.org/10.1098/rspb.2015.2947

Publication

Proceedings. Biological sciences
ISSN: 1471-2954
NlmUniqueID: 101245157
Country: England
Language: English
Volume: 283
Issue: 1829

Researcher Affiliations

Jones, Katrina Elizabeth
  • Center for Functional Anatomy and Evolution, Johns Hopkins University, 1830 East Monument St., Baltimore, MD 21205, USA katrinajones@fas.harvard.edu.

MeSH Terms

  • Adaptation, Biological
  • Animals
  • Biological Evolution
  • Body Size
  • Fossils / anatomy & histology
  • Gait / physiology
  • Horses / anatomy & histology
  • Horses / physiology
  • Locomotion / physiology
  • Lumbosacral Region / anatomy & histology
  • Lumbosacral Region / physiology
  • Models, Biological
  • Range of Motion, Articular / physiology
  • Running / physiology

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Citations

This article has been cited 8 times.
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