FREE SHIPPING over $40
OVER 9000 FIVE-STAR REVIEWS
5% OFF ALL SUBSCRIPTIONS
100% HAPPINESS GUARANTEE
Analyze Diet
0
Home / Equine Research Bank / Proc Biol Sci / Mechanics of evolutionary digit reduction in fossil horses (...
Proceedings. Biological sciences2017; 284(1861); 20171174; doi: 10.1098/rspb.2017.1174

Mechanics of evolutionary digit reduction in fossil horses (Equidae).

Abstract: Digit reduction is a major trend that characterizes horse evolution, but its causes and consequences have rarely been quantitatively tested. Using beam analysis on fossilized centre metapodials, we tested how locomotor bone stresses changed with digit reduction and increasing body size across the horse lineage. Internal bone geometry was captured from 13 fossil horse genera that covered the breadth of the equid phylogeny and the spectrum of digit reduction and body sizes, from to To account for the load-bearing role of side digits, a novel, continuous measure of digit reduction was also established-toe reduction index (TRI). Our results show that without accounting for side digits, three-toed horses as late as would have experienced physiologically untenable bone stresses. Conversely, when side digits are modelled as load-bearing, species at the base of the horse radiation through probably maintained a similar safety factor to fracture stress. We conclude that the centre metapodial compensated for evolutionary digit reduction and body mass increases by becoming more resistant to bending through substantial positive allometry in internal geometry. These results lend support to two historical hypotheses: that increasing body mass selected for a single, robust metapodial rather than several smaller ones; and that, as horse limbs became elongated, the cost of inertia from the side toes outweighed their utility for stabilization or load-bearing.
© 2017 The Author(s).
Get Full Text
Publication Date: 2017-08-25 PubMed ID: 28835559PubMed Central: PMC5577487DOI: 10.1098/rspb.2017.1174Google Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
LinkedInCopy
  • 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 investigates the evolution of digits reduction in horses and its impact on the locomotion and bone stress. It includes an analysis of fossils and introduces a unique measurement aspect, the Toe Reduction Index, to understand and account for the role of side digits in horses.

Objectives and Methodology

  • The primary goal of the study was to understand how the reduction in digits and increasing body size across the horse lineage impacted their locomotive bone stress.
  • This research was conducted using beam analysis on fossilized center metapodials from 13 different genera of fossil horses, spanning diverse sizes and stages of digit reduction across the equid phylogeny.
  • Unique to this study was the introduction of a new metric dubbed the ‘Toe Reduction Index (TRI)’, which offers a continuous measure of digit reduction.

Findings

  • The study found that, without considering side digits, horses (even as recent as 5 Myr ago) would have experienced untenable physiological bone stresses with three toes.
  • However, when side digits were included in the models as load-bearing, it was discovered that a similar safety factor was probably maintained with respect to fracture stress through the various stages of the horse evolutionary timeline, all the way to 5 Myr ago.
  • As such, the researchers concluded that the morphology of the central metapodial bone in horses evolved to compensate for the loss of digits and the increase in body mass by becoming more resistant to bending. This was evidenced by a significant positive allometry (change in proportion) noted in the internal geometry of the horse’s bone structure.

Conclusion

  • The study reiterated the long-held theory that the evolution of horse body mass prompted adaptation in the form of a single, sturdy metapodial bone instead of several smaller ones.
  • A second hypothesis also received support from this research which suggested that as horse limbs elongated through evolution, the cost of inertia from side toes outweighed their use for stabilization or load-bearing.

This study underscores how comprehensive analysis of fossil records can shed light on the evolutionary adaptations in species and help draw concrete conclusions about their consequent evolution.

Cite This Article

APA
McHorse BK, Biewener AA, Pierce SE. (2017). Mechanics of evolutionary digit reduction in fossil horses (Equidae). Proc Biol Sci, 284(1861), 20171174. https://doi.org/10.1098/rspb.2017.1174

Publication

Proceedings. Biological sciences
ISSN: 1471-2954
NlmUniqueID: 101245157
Country: England
Language: English
Volume: 284
Issue: 1861
PII: 20171174

Researcher Affiliations

McHorse, Brianna K
  • Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA bmchorse@fas.harvard.edu.
  • Concord Field Station, Department of Organismic and Evolutionary Biology, Harvard University, Bedford, MA 01730, USA.
Biewener, Andrew A
  • Concord Field Station, Department of Organismic and Evolutionary Biology, Harvard University, Bedford, MA 01730, USA.
Pierce, Stephanie E
  • Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.

MeSH Terms

  • Animals
  • Biological Evolution
  • Body Size
  • Equidae / anatomy & histology
  • Equidae / classification
  • Extremities
  • Fossils
  • Phylogeny
  • Weight-Bearing

Conflict of Interest Statement

We have no competing interests.

References

This article includes 47 references
  1. Clifford AB. The evolution of the unguligrade manus in artiodactyls. J. Vertebr. Paleontol. 30, 1827–1839.
    doi: 10.1080/02724634.2010.521216google scholar: lookup
  2. Cooper WJ, Steppan SJ. Developmental constraint on the evolution of marsupial forelimb morphology. Aust. J. Zool. 58, 1–15.
    doi: 10.1071/ZO09102google scholar: lookup
  3. de Bakker MA, Fowler DA, den Oude K, Dondorp EM, Navas MC, Horbanczuk JO, Sire JY, Szczerbińska D, Richardson MK. Digit loss in archosaur evolution and the interplay between selection and constraints.. Nature 2013 Aug 22;500(7463):445-8.
    doi: 10.1038/nature12336pubmed: 23831646google scholar: lookup
  4. Moore TY, Organ CL, Edwards SV, Biewener AA, Tabin CJ, Jenkins FA Jr, Cooper KL. Multiple phylogenetically distinct events shaped the evolution of limb skeletal morphologies associated with bipedalism in the jerboas.. Curr Biol 2015 Nov 2;25(21):2785-2794.
    doi: 10.1016/j.cub.2015.09.037pmc: PMC4743034pubmed: 26455300google scholar: lookup
  5. Saxena A, Towers M, Cooper KL. The origins, scaling and loss of tetrapod digits.. Philos Trans R Soc Lond B Biol Sci 2017 Feb 5;372(1713).
    doi: 10.1098/rstb.2015.0482pmc: PMC5182414pubmed: 27994123google scholar: lookup
  6. Young RL, Caputo V, Giovannotti M, Kohlsdorf T, Vargas AO, May GE, Wagner GP. Evolution of digit identity in the three-toed Italian skink Chalcides chalcides: a new case of digit identity frame shift.. Evol Dev 2009 Nov-Dec;11(6):647-58.
    doi: 10.1111/j.1525-142X.2009.00372.xpubmed: 19878286google scholar: lookup
  7. Coates MI, Clack JA. Polydactyly in the earliest known tetrapod limbs. Nature 347, 66–69.
    doi: 10.1038/347066a0google scholar: lookup
  8. Cooper KL, Sears KE, Uygur A, Maier J, Baczkowski KS, Brosnahan M, Antczak D, Skidmore JA, Tabin CJ. Patterning and post-patterning modes of evolutionary digit loss in mammals.. Nature 2014 Jul 3;511(7507):41-5.
    doi: 10.1038/nature13496pmc: PMC4228958pubmed: 24990742google scholar: lookup
  9. Lopez-Rios J, Duchesne A, Speziale D, Andrey G, Peterson KA, Germann P, Unal E, Liu J, Floriot S, Barbey S, Gallard Y, Müller-Gerbl M, Courtney AD, Klopp C, Rodriguez S, Ivanek R, Beisel C, Wicking C, Iber D, Robert B, McMahon AP, Duboule D, Zeller R. Attenuated sensing of SHH by Ptch1 underlies evolution of bovine limbs.. Nature 2014 Jul 3;511(7507):46-51.
    doi: 10.1038/nature13289pubmed: 24990743google scholar: lookup
  10. Cooper LN, Berta A, Dawson SD, Reidenberg JS. Evolution of hyperphalangy and digit reduction in the cetacean manus.. Anat Rec (Hoboken) 2007 Jun;290(6):654-72.
    doi: 10.1002/ar.20532pubmed: 17516431google scholar: lookup
  11. Shapiro MD, Shubin NH, Downs JP. Limb diversity and digit reduction in reptilian evolution. .
  12. Moore TY, Biewener AA. Outrun or Outmaneuver: Predator-Prey Interactions as a Model System for Integrating Biomechanical Studies in a Broader Ecological and Evolutionary Context.. Integr Comp Biol 2015 Dec;55(6):1188-97.
    doi: 10.1093/icb/icv074pubmed: 26117833google scholar: lookup
  13. MacFadden BJ. Fossil horses: systematics, paleobiology, and evolution of the family Equidae. .
  14. Simpson GG. Horses: the story of the horse family in the modern world and through sixty million years. .
  15. Janis CM, Wilhelm PB. Were there mammalian pursuit predators in the Tertiary? Dances with wolf avatars. J. Mamm. Evol. 1, 103–125.
    doi: 10.1007/BF01041590google scholar: lookup
  16. Shotwell JA. Late Tertiary biogeography of horses in the northern Great Basin. J. Paleontol. 35, 203–217.
  17. Thomason JJ. The functional morphology of the manus in the tridactyl equids Merychippus and Mesohippus: paleontological inferences from neontological models. J. Vertebr. Paleontol. 6, 143–161.
    doi: 10.1080/02724634.1986.10011607google scholar: lookup
  18. Biewener AA. Muscle-tendon stresses and elastic energy storage during locomotion in the horse.. Comp Biochem Physiol B Biochem Mol Biol 1998 May;120(1):73-87.
    doi: 10.1016/S0305-0491(98)00024-8pubmed: 9787779google scholar: lookup
  19. Camp CL, Smith N. Phylogeny and functions of the digital ligaments of the horse. Mem. Univ. Calif. 3, 69–124.
  20. Sondaar PY. The osteology of the manus of fossil and recent Equidae, with special reference to phylogeny and function. Verhandelingen der Koninklijke Nederlandse akademie van wetenschappen 25, 1–76.
  21. Thomason JJ. Estimation of locomotory forces and stresses in the limb bones of recent and extinct equids. Paleobiology 11, 209–220.
    doi: 10.1017/S0094837300011519google scholar: lookup
  22. Renders E. The gait of Hipparion sp. from fossil footprints in Laetoli, Tanzania.. Nature 1984 Mar 8-14;308(5955):179-81.
    doi: 10.1038/308179a0pubmed: 6700720google scholar: lookup
  23. Biewener AA. Biomechanics of mammalian terrestrial locomotion.. Science 1990 Nov 23;250(4984):1097-103.
    doi: 10.1126/science.2251499pubmed: 2251499google scholar: lookup
  24. Rubin CT, Lanyon LE. Dynamic strain similarity in vertebrates; an alternative to allometric limb bone scaling.. J Theor Biol 1984 Mar 21;107(2):321-7.
    doi: 10.1016/S0022-5193(84)80031-4pubmed: 6717041google scholar: lookup
  25. Biewener AA, Thomason J, Lanyon LE. Mechanics of locomotion and jumping in the forelimb of the horse (Equus): in vivo stress developed in the radius and metacarpus. J. Zool. 201, 67–82.
    doi: 10.1111/j.1469-7998.1983.tb04261.xgoogle scholar: lookup
  26. Biewener AA, Thomason JJ, Lanyon LE. Mechanics of locomotion and jumping in the horse (Equus): in vivo stress in the tibia and metatarsus. J. Zool. 214, 547–565.
    doi: 10.1111/j.1469-7998.1988.tb03759.xgoogle scholar: lookup
  27. MacLaren JA, Nauwelaerts S. A three-dimensional morphometric analysis of upper forelimb morphology in the enigmatic tapir (Perissodactyla: Tapirus) hints at subtle variations in locomotor ecology.. J Morphol 2016 Nov;277(11):1469-1485.
    doi: 10.1002/jmor.20588pubmed: 27519626google scholar: lookup
  28. Doube M, Kłosowski MM, Arganda-Carreras I, Cordelières FP, Dougherty RP, Jackson JS, Schmid B, Hutchinson JR, Shefelbine SJ. BoneJ: Free and extensible bone image analysis in ImageJ.. Bone 2010 Dec;47(6):1076-9.
    doi: 10.1016/j.bone.2010.08.023pmc: PMC3193171pubmed: 20817052google scholar: lookup
  29. Schneider CA, Rasband WS, Eliceiri KW. NIH Image to ImageJ: 25 years of image analysis.. Nat Methods 2012 Jul;9(7):671-5.
    doi: 10.1038/nmeth.2089pmc: PMC5554542pubmed: 22930834google scholar: lookup
  30. Cuff AR, Sparkes EL, Randau M, Pierce SE, Kitchener AC, Goswami A, Hutchinson JR. The scaling of postcranial muscles in cats (Felidae) II: hindlimb and lumbosacral muscles.. J Anat 2016 Jul;229(1):142-52.
    doi: 10.1111/joa.12474pmc: PMC5341591pubmed: 27080703google scholar: lookup
  31. Warton DI, Duursma RA, Falster DS, Taskinen S. smatr 3—an R package for estimation and inference about allometric lines. Methods. Ecol. Evol. 3, 257–259.
    doi: 10.1111/j.2041-210X.2011.00153.xgoogle scholar: lookup
  32. Doube M, Yen SC, Kłosowski MM, Farke AA, Hutchinson JR, Shefelbine SJ. Whole-bone scaling of the avian pelvic limb.. J Anat 2012 Jul;221(1):21-9.
    doi: 10.1111/j.1469-7580.2012.01514.xpmc: PMC3390530pubmed: 22606941google scholar: lookup
  33. MacFadden BJ. Fossil horses from ‘Eohippus’ (Hyracotherium) to Equus: scaling, Cope's Law, and the evolution of body size. Paleobiology 12, 355–369.
    doi: 10.1017/S0094837300003109google scholar: lookup
  34. Garland T, Janis CM. Does metatarsal/femur ratio predict maximal running speed in cursorial mammals?. J. Zool. 229, 133.
    doi: 10.1111/j.1469-7998.1993.tb02626.xgoogle scholar: lookup
  35. Damuth J. Problems in estimating body masses of archaic ungulates using dental measurements. .
  36. Janis CM, Gordon IJ, Illius AW. Modelling equid/ruminant competition in the fossil record. Hist. Biol. 8, 15–29.
    doi: 10.1080/10292389409380469google scholar: lookup
  37. Rumph PF, Lander JE, Kincaid SA, Baird DK, Kammermann JR, Visco DM. Ground reaction force profiles from force platform gait analyses of clinically normal mesomorphic dogs at the trot.. Am J Vet Res 1994 Jun;55(6):756-61.
    pubmed: 7944010
  38. Brown NA, Pandy MG, Buford WL, Kawcak CE, McIlwraith CW. Moment arms about the carpal and metacarpophalangeal joints for flexor and extensor muscles in equine forelimbs.. Am J Vet Res 2003 Mar;64(3):351-7.
    doi: 10.2460/ajvr.2003.64.351pubmed: 12661877google scholar: lookup
  39. Bullimore SR, Burn JF. Dynamically similar locomotion in horses.. J Exp Biol 2006 Feb;209(Pt 3):455-65.
    doi: 10.1242/jeb.02029pubmed: 16424095google scholar: lookup
  40. Biewener AA. Musculoskeletal design in relation to body size.. J Biomech 1991;24 Suppl 1:19-29.
    doi: 10.1016/0021-9290(91)90374-Vpubmed: 1791177google scholar: lookup
  41. Currey JD. The mechanical adaptations of bones. .
  42. Biewener AA. Scaling body support in mammals: limb posture and muscle mechanics.. Science 1989 Jul 7;245(4913):45-8.
    doi: 10.1126/science.2740914pubmed: 2740914google scholar: lookup
  43. Tucker ST, Otto RE, Joeckel RM, Voorhies MR. The geology and paleontology of Ashfall Fossil Beds, a late Miocene (Clarendonian) mass-death assemblage, Antelope County and adjacent Knox County, Nebraska, USA. Field Guides 36, 1–22.
    doi: 10.1130/2014.0036(01)google scholar: lookup
  44. Strömberg CA. Evolution of grasses and grassland ecosystems. Annu. Rev. Earth. Planet. Sci. 39, 517–544.
    doi: 10.1146/annurev-earth-040809-152402google scholar: lookup
  45. Retallack GJ. Cenozoic paleoclimate on land in North America. J. Geol. 115, 271–294.
    doi: 10.1086/512753google scholar: lookup
  46. Alexander R. Terrestrial locomotion. .
  47. McHorse BK, Biewener AA, Pierce SE. Mechanics of evolutionary digit reduction in fossil horses (Equidae).. Proc Biol Sci 2017 Aug 30;284(1861).
    doi: 10.5061/dryad.4v130pmc: PMC5577487pubmed: 28835559google scholar: lookup

Citations

This article has been cited 11 times.
Subscribe to our newsletter
Join 99,357 horse owners like you who receive our email updates on horse health and nutrition.