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Vincelette AR, Renders E, Scott KM, Falkingham PL, Janis CM. Hipparion tracks and horses' toes: the evolution of the equid single hoof. ROYAL SOCIETY OPEN SCIENCE 2023; 10:230358. [PMID: 37351494 PMCID: PMC10282582 DOI: 10.1098/rsos.230358] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Accepted: 05/30/2023] [Indexed: 06/24/2023]
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 Hipparion 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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Affiliation(s)
| | - Elise Renders
- Department of Functional Morphology, Faculty of Veterinary Medicine, Utrecht University (Ret.), Utrecht, 3584 CM, The Netherlands
| | - Kathleen M. Scott
- Department of Cell Biology and Neuroscience, Rutgers University, New Brunswick, 08854, NJ, USA
| | - Peter L. Falkingham
- School of Biological and Environmental Sciences, Liverpool John Moores University, Liverpool, L3 3AF, UK
| | - Christine M. Janis
- 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
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2
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Bhattacharjee S. The osseous fusion patterns in an equine limb: A theoretical deconstruction of the evolutionary mechanisms. Biosystems 2023; 225:104871. [PMID: 36858109 DOI: 10.1016/j.biosystems.2023.104871] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2022] [Revised: 02/24/2023] [Accepted: 02/24/2023] [Indexed: 03/02/2023]
Abstract
Adaptations in equine limbs, including fusion of its bones, such as the metapodials II and IV (splint bones) with metapodial III (cannon bone), have been debated. It is argued that cursorial adaptations in equine limbs with a progressive reduction in the number of digits lighten up the limbs and facilitate fast running. Similar fusions in other bones, such as the radius and ulna, tend to exhibit similar traits. For example, the fusion often occurs in a disto-proximal direction while leaving sharp ridges. This article proposes a model to understand the biomechanical advantages that a fused symmetric system of cannon and splint bones offers and tries to investigate osseous fusion from an evolutionary perspective. It demonstrated the uniqueness of this system from the context of symmetry and the presence of an array of parallel axes of rotation in equine limbs that amplifies the kinetic energy by maximizing the moment of inertia. The model highlighted the robustness of such an evolutionary mechanism in place and elucidated why it is a preferable construct. Furthermore, the discourse proposes a zipping action to describe the osseous fusion before making predictions on where the equine limb adaptations are perhaps heading.
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Affiliation(s)
- Sourav Bhattacharjee
- School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland.
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3
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Costa da Silva RG, Mishra AP, Riggs CM, Doube M. Classification of racehorse limb radiographs using deep convolutional neural networks. Vet Rec Open 2023; 10:e55. [PMID: 36726400 PMCID: PMC9884469 DOI: 10.1002/vro2.55] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Revised: 12/07/2022] [Accepted: 12/16/2022] [Indexed: 01/30/2023] Open
Abstract
Purpose To assess the capability of deep convolutional neural networks to classify anatomical location and projection from a series of 48 standard views of racehorse limbs. Materials and methods Radiographs (N = 9504) of horse limbs from image sets made for veterinary inspections by 10 independent veterinary clinics were used to train, validate and test (116, 40 and 42 radiographs, respectively) six deep learning architectures available as part of the open source machine learning framework PyTorch. The deep learning architectures with the best top-1 accuracy had the batch size further investigated. Results Top-1 accuracy of six deep learning architectures ranged from 0.737 to 0.841. Top-1 accuracy of the best deep learning architecture (ResNet-34) ranged from 0.809 to 0.878, depending on batch size. ResNet-34 (batch size = 8) achieved the highest top-1 accuracy (0.878) and the majority (91.8%) of misclassification was due to laterality error. Class activation maps indicated that joint morphology, not side markers or other non-anatomical image regions, drove the model decision. Conclusions Deep convolutional neural networks can classify equine pre-import radiographs into the 48 standard views including moderate discrimination of laterality, independent of side marker presence.
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Affiliation(s)
| | - Ambika Prasad Mishra
- Department of Infectious Diseases and Public HealthCity University of Hong KongHong Kong SARChina
| | | | - Michael Doube
- Department of Infectious Diseases and Public HealthCity University of Hong KongHong Kong SARChina
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4
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Smith S, Yohe LR, Solounias N. The bony cap and its distinction from the distal phalanx in humans, cats, and horses. PeerJ 2023; 11:e14352. [PMID: 36643632 PMCID: PMC9838202 DOI: 10.7717/peerj.14352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Accepted: 10/17/2022] [Indexed: 01/12/2023] Open
Abstract
It has been recognized as early as the Victorian era that the apex of the distal phalanx has a distinct embryological development from the main shaft of the distal phalanx. Recent studies in regenerative medicine have placed an emphasis on the role of the apex of the distal phalanx in bone regrowth. Despite knowledge about the unique aspects of the distal phalanx, all phalanges are often treated as equivalent. Our morphological study reiterates and highlights the special anatomical and embryological properties of the apex of the distal phalanx, and names the apex "the bony cap" to distinguish it. We posit that the distal phalanx shaft is endochondral, while the bony cap is intramembranous and derived from the ectodermal wall. During development, the bony cap may be a separate structure that will fuse to the endochondral distal phalanx in the adult, as it ossifies well before the distal phalanges across taxa. Our study describes and revives the identity of the bony cap, and we identify it in three mammalian species: humans, cats, and horses (Homo sapiens, Felis catus domestica, and Equus caballus). During the embryonic period, we show the bony cap has a thimble-like shape that surrounds the proximal endochondral distal phalanx. The bony cap may thus play an inductive role in the differentiation of the corresponding nail, claw, or hoof (keratin structures) of the digit. When it is not present or develops erroneously, the corresponding keratin structures are affected, and regeneration is inhibited. By terming the bony cap, we hope to inspire more attention to its distinct identity and role in regeneration.
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Affiliation(s)
- Shannon Smith
- College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, New York, United States
| | - Laurel R. Yohe
- Bioinformatics and Genomics, University of North Carolina at Charlotte, Charlotte, North Carolina, United States,Earth and Planetary Sciences, Yale University, New Haven, Connecticut, United States,North Carolina Research Center, Kannapolis, North Carolina, United States,Ecology and Evolution, State University of New York at Stony Brook, Stony Brook, New York, United States
| | - Nikos Solounias
- College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, New York, United States,Department of Paleontology, American Museum of Natural History, New York, NY, United States
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5
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Xu B, Yang G, Jiao B, Zhu H. Analysis of ancient and modern horse genomes reveals the critical impact of lncRNA-mediated epigenetic regulation on horse domestication. Front Genet 2022; 13:944933. [PMID: 36276948 PMCID: PMC9579347 DOI: 10.3389/fgene.2022.944933] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Accepted: 08/08/2022] [Indexed: 11/22/2022] Open
Abstract
Background: The domestication of horses has played critical roles in human civilizations. The excavation of ancient horse DNA provides crucial data for studying horse domestication. Studies of horse domestication can shed light on the general mechanisms of animal domestication. Objective: We wish to explore the gene transcription regulation by long noncoding RNAs (lncRNAs) that influence horse domestication. Methods: First, we assembled the ancient DNA sequences of multiple horses at different times and the genomes of horses, donkeys, and Przewalski horses. Second, we extracted sequences of lncRNA genes shared in ancient horses and sequences of lncRNA genes and the promoter regions of domestication-critical genes shared in modern horses, modern donkeys, and Przewalski horses to form two sample groups. Third, we used the LongTarget program to predict potential regulatory interactions between these lncRNAs and these domestication-critical genes and analyzed the differences between the regulation in ancient/modern horses and between horses/donkeys/Przewalski horses. Fourth, we performed functional enrichment analyses of genes that exhibit differences in epigenetic regulation. Results: First, genes associated with neural crest development and domestication syndrome are important targets of lncRNAs. Second, compared with undomesticated Przewalski horses, more lncRNAs participate in the epigenetic regulation in modern horses and donkeys, suggesting that domestication is linked to more epigenetic regulatory changes. Third, lncRNAs’ potential target genes in modern horses are mainly involved in two functional areas: 1) the nervous system, behavior, and cognition, and 2) muscle, body size, cardiac function, and metabolism. Conclusion: Domestication is linked to substantial epigenetic regulatory changes. Genes associated with neural crest development and domestication syndrome underwent noticeable lncRNA-mediated epigenetic regulation changes during horse domestication.
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Affiliation(s)
- Baoyan Xu
- Bioinformatics Section, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China
- Medical Engineering Department, Integrated Hospital of Traditional Chinese Medicine, Southern Medical University, Guangzhou, China
| | - Guixian Yang
- Zhujiang Hospital, Southern Medical University, Guangzhou, China
| | - Baowei Jiao
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Science, Kunming, China
| | - Hao Zhu
- Bioinformatics Section, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China
- *Correspondence: Hao Zhu,
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6
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Azarpeykan S, Gee EK, Thompson KG, Dittmer KE. Undetectable vitamin D 3 in equine skin irradiated with ultraviolet light. J Equine Sci 2022; 33:45-49. [PMID: 36196139 PMCID: PMC9522623 DOI: 10.1294/jes.33.45] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Accepted: 07/22/2022] [Indexed: 11/29/2022] Open
Abstract
Vitamin D requirements for most animals are expected to be fulfilled through daily
exposure of the skin to solar ultraviolet B radiation. The synthesis of vitamin
D3 in skin depends on different factors including melanin pigmentation, the
amount of UVB radiation reaching the skin, type of clothing/hair coat, latitude and
altitude, season, and time of day. Alternatively vitamin D2 may be obtained
from UVB irradiated pasture species. Recent studies have shown that in unsupplemented
grazing horses 25-hydroxyvitamin D2 is the predominant form of vitamin D in
plasma, and that 25OHD3 is undetectable suggesting horses may rely on diet to
obtain vitamin D. In order to mimic the natural environment of skin to sunlight exposure,
five equine and two ovine devitalized skin samples were irradiated with 5 J/cm2
of UVB light followed by measurement of 7-dehydrocholesterol (7-DHC) and vitamin
D3 concentrations using reverse-phase high pressure liquid chromatography
(HPLC). HPLC revealed the presence of 7-DHC in the skin of both horses and sheep. Vitamin
D3 was undetectable in both ovine and equine skin prior to irradiation, but
after irradiation with UVB light, ovine skin showed an increase in vitamin D3
concentration (mean 0.16 ± 0.07 µg/g), whereas vitamin D3 was undetectable in
equine skin. These results provide additional evidence that horses make negligible
quantities of vitamin D3 in their skin after exposure to UVB light and may
therefore rely on their diet as a primary source of vitamin D.
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Affiliation(s)
- Sara Azarpeykan
- School of Veterinary Science, Tennent Drive, Massey University, Palmerston North 4442, New Zealand
| | - Erica K Gee
- School of Veterinary Science, Tennent Drive, Massey University, Palmerston North 4442, New Zealand
| | - Keith G Thompson
- School of Veterinary Science, Tennent Drive, Massey University, Palmerston North 4442, New Zealand
| | - Keren E Dittmer
- School of Veterinary Science, Tennent Drive, Massey University, Palmerston North 4442, New Zealand
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7
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Gerard MP. Anatomy and Physiology of the Equine Foot. Vet Clin North Am Equine Pract 2021; 37:529-548. [PMID: 34674910 DOI: 10.1016/j.cveq.2021.07.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
This article provides an overview of foot anatomy and physiology, with a focus on fundamental knowledge. The foot is defined as the epidermal hoof capsule and all structures enveloped by the capsule. The anatomy is described using terminology published in Nomina Anatomica Veterinaria.
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Affiliation(s)
- Mathew P Gerard
- Veterinary Anatomy, Department of Molecular Biomedical Sciences, North Carolina State University, College of Veterinary Medicine, 1060 William Moore Drive, Raleigh, NC 27607, USA.
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8
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Howenstine AO, Sadier A, Anthwal N, Lau CL, Sears KE. Non-model systems in mammalian forelimb evo-devo. Curr Opin Genet Dev 2021; 69:65-71. [PMID: 33684847 PMCID: PMC8364859 DOI: 10.1016/j.gde.2021.01.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Revised: 01/26/2021] [Accepted: 01/28/2021] [Indexed: 01/09/2023]
Abstract
Mammal forelimbs are highly diverse, ranging from the elongated wing of a bat to the stout limb of the mole. The mammal forelimb has been a long-standing system for the study of early developmental patterning, proportional variation, shape change, and the reduction of elements. However, most of this work has been performed in mice, which neglects the wide variation present across mammal forelimbs. This review emphasizes the critical role of non-model systems in limb evo-devo and highlights new emerging models and their potential. We discuss the role of gene networks in limb evolution, and touch on functional analyses that lay the groundwork for further developmental studies. Mammal limb evo-devo is a rich field, and here we aim to synthesize the findings of key recent works and the questions to which they lead.
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Affiliation(s)
- Aidan O Howenstine
- Department of Ecology and Evolutionary Biology, University of California at Los Angeles, Los Angeles, CA, 90095, United States
| | - Alexa Sadier
- Department of Ecology and Evolutionary Biology, University of California at Los Angeles, Los Angeles, CA, 90095, United States
| | - Neal Anthwal
- Department of Ecology and Evolutionary Biology, University of California at Los Angeles, Los Angeles, CA, 90095, United States; Centre for Craniofacial and Regenerative Biology, King's CollegeLondon, 27th Floor Guy's Tower, London, SE1 9RT, UK
| | - Clive Lf Lau
- Department of Ecology and Evolutionary Biology, University of California at Los Angeles, Los Angeles, CA, 90095, United States
| | - Karen E Sears
- Department of Ecology and Evolutionary Biology, University of California at Los Angeles, Los Angeles, CA, 90095, United States.
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9
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Abstract
Abstract
Evolution has shaped the limbs of hoofed animals in specific ways. In artiodactyls, it is the common assumption that the metatarsal is composed of the fusion of digits III and IV, whereas the other three digits have been lost or are highly reduced. However, evidence from the fossil record and internal morphology of the metatarsal challenges these assumptions. Furthermore, only a few taxonomic groups have been analysed. In giraffes, we discovered that all five digits are present in the adult metatarsal and are highly fused and modified rather than lost. We examined high-resolution micro-computed tomography scans of the metatarsals of two mid and late Miocene giraffid fossils and the extant giraffe and okapi. In all the Giraffidae analysed, we found a combination of four morphologies: (1) four articular facets; (2) four or, in most cases, five separate medullary cavities internally; (3) a clear, small digit I; and (4) in the two fossil taxa of unknown genus, the presence of external elongated grooves where the fusions of digits II and V have taken place. Giraffa and Okapia, the extant Giraffidae, show a difference from all the extinct taxa in having more flattened digits tightly packed together, suggesting convergent highly fused digits despite divergent ecologies and locomotion. These discoveries provide evidence that enhances our understanding of how bones fuse and call into question current hypotheses of digit loss.
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Affiliation(s)
- Laurel R Yohe
- Department of Earth and Planetary Sciences, Yale University, New Haven, CT, USA
| | - Nikos Solounias
- Department of Paleontology, American Museum of Natural History, New York, NY, USA
- Department of Anatomy, New York Institute of Technology, College of Osteopathic Medicine, Old Westbury, NY, USA
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10
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Kavanagh KD, Bailey CS, Sears KE. Evidence of five digits in embryonic horses and developmental stabilization of tetrapod digit number. Proc Biol Sci 2020; 287:20192756. [PMID: 32019446 DOI: 10.1098/rspb.2019.2756] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Previous work comparing the developmental mechanisms involved in digit reduction in horses with other mammals reported that horses have only a 'single digit', with two flanking metapodials identified as remnants of digit II and IV. Here we show that early Equus embryos go through a stage with five digit condensations, and that the flanking splint metapodials result from fusions of the two anterior digits I and II and the two posterior digits IV and V, in a striking parallel between ontogeny and phylogeny. Given that even this most extreme case of digit reduction exhibits primary pentadactyly, we re-examined the initial stages of digit condensation of all digit-reduced tetrapods where data are available and found that in all cases, five or four digits initiate (four with digit I missing). The persistent pentadactyl initiation in the horse and other digit-reduced modern taxa underscores a durable developmental stability at the initiation of digits. The digit evodevo model may help illuminate the biological circumstances under which organ systems become highly stabilized versus highly plastic.
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Affiliation(s)
- Kathryn D Kavanagh
- Department of Biology, University of Massachusetts Dartmouth, Dartmouth, MA, USA
| | - C Scott Bailey
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607, USA
| | - Karen E Sears
- Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA, USA
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11
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McHorse BK, Biewener AA, Pierce SE. The Evolution of a Single Toe in Horses: Causes, Consequences, and the Way Forward. Integr Comp Biol 2020; 59:638-655. [PMID: 31127281 DOI: 10.1093/icb/icz050] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Horses are a classic example of macroevolution in three major traits-large body size, tall-crowned teeth (hypsodonty), and a single toe (monodactyly)-but how and why monodactyly evolved is still poorly understood. Existing hypotheses usually connect digit reduction in horses to the spread and eventual dominance of open-habitat grasslands, which took over from forests during the Cenozoic; digit reduction has been argued to be an adaptation for speed, locomotor economy, stability, and/or increased body size. In this review, we assess the evidence for these (not necessarily mutually exclusive) hypotheses from a variety of related fields, including paleoecology, phylogenetic comparative methods, and biomechanics. Convergent evolution of digit reduction, including in litopterns and artiodactyls, is also considered. We find it unlikely that a single evolutionary driver was responsible for the evolution of monodactyly, because changes in body size, foot posture, habitat, and substrate are frequently found to influence one another (and to connect to broader potential drivers, such as changing climate). We conclude with suggestions for future research to help untangle the complex dynamics of this remarkable morphological change in extinct horses. A path forward should combine regional paleoecology studies, quantitative biomechanical work, and make use of convergence and modern analogs to estimate the relative contributions of potential evolutionary drivers for digit reduction.
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Affiliation(s)
- Brianna K McHorse
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.,Concord Field Station, Harvard University, Bedford, MA 01730, USA.,Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, USA
| | - Andrew A Biewener
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.,Concord Field Station, Harvard University, Bedford, MA 01730, USA
| | - Stephanie E Pierce
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.,Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, USA
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12
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May-Davis S, Vermeulen Z, Brown WY. A Primitive Trait in Two Breeds of Equus Caballus Revealed by Comparative Anatomy of the Distal Limb. Animals (Basel) 2019; 9:ani9060355. [PMID: 31197123 PMCID: PMC6617308 DOI: 10.3390/ani9060355] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2019] [Revised: 05/31/2019] [Accepted: 06/04/2019] [Indexed: 11/25/2022] Open
Abstract
Simple Summary Understanding the complexities and evolutionary links between extinct and extant equids has been vital to genetic conservation and preservation of primitive traits. As domestication of the equid expanded, the loss of primitive traits that ensured survival in a wild environment has not been documented. In this study, the presence of functional interosseous muscle II and IV in the distal limb has been reported, and yet its existence could only be confirmed in relatives and two closely bred descendants of the extinct Tarpan. The morphology described was ligamentous in structure displaying clear longitudinal fibres with a skeletal origin and soft tissue insertion into the medial and lateral branches of the interosseous muscle III (suspensory ligament) dorsal to the sesamoids, similar in orientation to the flexor digitorum profundus ligamentum accessorium (inferior check ligament). Hence, providing a functional medial and lateral stability to the metacarpophalangeal joint (fetlock joint), which equates to one of the functions of the medial and lateral digits in the Mesohippus and Merychippus. The comparable anatomic links between species of the same family that experienced geographical isolation yet display structural conformity appears to be in response to a specific environment. Surmising this potential remnant of functional evolution is a primitive trait and not a breed anomaly. Abstract The 55-million-year history of equine phylogeny has been well-documented from the skeletal record; however, this is less true for the soft tissue structures that are now vestigial in modern horse. A recent study reported that two ligamentous structures resembling functional interosseous muscle II and IV were evident in Dutch Konik horses. The current study investigates this finding and compares it to members of the genus Equus to identify either a breed anomaly or functional primitive trait. Distal limbs (n = 574) were dissected from four species of Equus; E. caballus, E. asinus, E. przewalskii and E. quagga boehmi. E. caballus is represented by 18 breeds of horse, including the primitive Dutch Konik’. The interosseous muscle II and IV were evident in all four species, but only two breeds of E. caballus expressed this trait-the Dutch Konik and Bosnian Mountain Horse. These two breeds were the only close descendants of the extinct Equus ferus ferus (Tarpan) represented in this study. In conclusion, the interosseous muscle II and IV originated from the distal nodule of metacarpal II and IV, respectively, and inserted into the corresponding branches of interosseous muscle III proximal to the sesamoids. This suggests a functional role in medial and lateral joint stability and a primitive trait in modern equids.
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Affiliation(s)
- Sharon May-Davis
- Canine and Equine Research Group, University of New England, Armidale, NSW 2351, Australia.
| | | | - Wendy Y Brown
- Canine and Equine Research Group, University of New England, Armidale, NSW 2351, Australia.
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