Equidae

Equidae; Temporal range: 50.3–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N Early Eocene - Recent
	Persian onager
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Superfamily:	Equoidea
Family:	Equidae; Gray, 1821
Subfamilies
	†Anchitheriinae; Equinae;

Equidae (commonly known as the horse family) is the taxonomic family of horses and related animals, including the extant horses, asses, and zebras, and many other species known only from fossils. The family evolved around 50 million years ago from a small, multi-toed ungulate into larger, single-toed animals. All extant species are in the genus Equus, which originated in North America. Equidae belongs to the order Perissodactyla, which includes the extant tapirs and rhinoceros, and several extinct families. It is more specifically grouped within the superfamily Equoidea, the only other family being the extinct Palaeotheriidae.

The term equid refers to any member of this family, including any equine.

Evolution

The oldest known fossils assigned to Equidae were found in North America, and date from the early Eocene epoch, 54 million years ago. They were once assigned to the genus Hyracotherium, but the type species of that genus is now regarded as a palaeothere. The other species have been split off into different genera. These early equids were fox-sized animals with three toes on the hind feet, and four on the front feet. They were herbivorous browsers on relatively soft plants, and already adapted for running. The complexity of their brains suggest that they already were alert and intelligent animals.^[2] Later species reduced the number of toes, and developed teeth more suited for grinding up grasses and other tough plant food.

The equids, like other perissodactyls, are hindgut fermenters. They have evolved specialized teeth that cut and shear tough plant matter to accommodate their fibrous diet.^[3] Their seemingly inefficient digestion strategy is a result of their size at the time of its evolution,^[4] as they would have already had to be relatively large mammals to be supported on such a strategy.

The family became relatively diverse during the Miocene epoch,^[5] with many new species appearing. By this time, equids were more truly horse like, having developed the typical body shape of the modern animals.^[6] Many of these species bore the main weight of their bodies on their central third toe, with the others becoming reduced and barely touching the ground, if at all. The sole surviving genus, Equus, had evolved by the early Pleistocene epoch, and spread rapidly through the world.^[7]

Classification

Order Perissodactyla (In addition to Equidae, Perissodactyla includes four species of tapir in a single genus, as well as five living species (belonging to four genera) of rhinoceros.) † indicates extinct taxa.
- Family Equidae
  - Subfamily †Hyracotheriinae
    - Genus †Epihippus
    - Genus †Haplohippus
    - Genus †Eohippus
    - Genus †Minippus^[8]
    - Genus †Orohippus
    - Genus †Pliolophus
    - Genus †Protorohippus
    - Genus †Sifrhippus
    - Genus †Xenicohippus^[8]
  - Subfamily †Anchitheriinae
    - Genus †Anchitherium
    - Genus †Archaeohippus
    - Genus †Desmatippus
    - Genus †Hypohippus
    - Genus †Kalobatippus
    - Genus †Megahippus
    - Genus †Mesohippus
    - Genus †Miohippus
    - Genus †Parahippus
    - Genus †Sinohippus
  - Subfamily Equinae
    - Genus †Merychippus
    - Genus †Scaphohippus
    - Genus †Acritohippus
    - Tribe †Hipparionini
      - Genus †Eurygnathohippus
      - Genus †Hipparion
      - Genus †Hippotherium
      - Genus †Nannippus
      - Genus †Neohipparion
      - Genus †Proboscidipparion
      - Genus †Pseudhipparion
    - Tribe Equini
      - Genus †Haringtonhippus^[9]
      - Genus †Heteropliohippus^[10]
      - Genus †Parapliohippus^[10]
      - Subtribe Protohippina
        Genus †Calippus
        
        Genus †Protohippus
      - Subtribe Equina
        Genus †Astrohippus
        
        Genus †Dinohippus
        
        Genus Equus (22 species, 7 extant)
        Equus ferus Wild horse
        Equus ferus caballus Domestic horse
        
        †Equus ferus ferus Tarpan
        
        Equus ferus przewalskii Przewalski's horse
        
        †Equus algericus^[11]
        
        †Equus alaskae
        
        †Equus lambei Yukon wild horse
        
        †Equus niobrarensis
        
        †Equus scotti
        
        †Equus conversidens Mexican horse
        
        †Equus semiplicatus
        
        Subgenus †Amerhippus (this subgenus and its species are possibly synonymous with E. ferus)^[12]
        †Equus andium
        
        †Equus neogeus
        
        †Equus insulatus
        
        Subgenus Asinus
        Equus africanus African wild ass
        Equus africanus africanus Nubian wild ass
        
        Equus africanus asinus Domestic donkey
        
        †Equus africanus atlanticus Atlas wild ass
        
        Equus africanus somalicus Somali wild ass
        
        Equus hemionus Onager or Asiatic wild ass
        Equus hemionus hemionus Mongolian wild ass
        
        †Equus hemionus hemippus Syrian wild ass
        
        Equus hemionus khur Indian wild ass
        
        Equus hemionus kulan Turkmenian kulan
        
        Equus hemionus onager Persian onager
        
        Equus kiang Kiang
        Equus kiang chu Northern kiang
        
        Equus kiang kiang Western kiang
        
        Equus kiang holdereri Eastern kiang
        
        Equus kiang polyodon Southern kiang
        
        †Equus hydruntinus European ass
        
        †Equus altidens
        
        †Equus tabeti
        
        †Equus melkiensis
        
        †Equus graziosii
        
        Subgenus Hippotigris^[a]
        Equus grevyi Grévy's zebra
        
        †Equus koobiforensis
        
        †Equus oldowayensis
        
        Equus quagga Plains zebra
        Equus quagga boehmi Grant's zebra
        
        Equus quagga borensis Maneless zebra
        
        Equus quagga burchellii Burchell's zebra
        
        Equus quagga chapmani Chapman's zebra
        
        Equus quagga crawshayi Crawshay's zebra
        
        †Equus quagga quagga Quagga
        
        Equus quagga selousi Selous' zebra
        
        Equus zebra Mountain zebra
        Equus zebra hartmannae Hartmann's mountain zebra
        
        Equus zebra zebra Cape mountain zebra
        
        †Equus capensis
        
        †Equus mauritanicus
        
        Subgenus †Parastylidequus
        †Equus parastylidens Mooser's horse
        
        †Subgenus Sussemionus^[15]
        †Equus ovodovi^[16]
        
        incertae sedis
        †Equus simplicidens Hagerman horse
        
        †Equus cumminsii
        
        †Equus livenzovensis
        
        †Equus sanmeniensis
        
        †Equus teilhardi
        
        †Equus numidicus
        
        †Equus plicidens
        
        †Equus cedralensis
        
        †Equus stenonis group
        †Equus stenonis Stenon zebra
        †Equus stenonis guthi
        
        †Equus stenonis senezensis
        
        †Equus stenonis pamirensis (Hippotigris pamirensis)
        
        †Equus stenonis petraloniensis
        
        †Equus stenonis vireti
        
        †Equus sivalensis
        
        †Equus stehlini
        
        †Equus sussenbornensis
        
        †Equus verae
        
        †Equus namadicus
        
        †subgenus Allozebra
        †Equus (A.) occidentalis western horse
        
        †Equus (A.) excelsus
        †subgenus Hesperohippus
        †Equus (H.) pacificus
        
        †Equus (H.) mexicanus
        
        †Equus complicatus
        
        †Equus fraternus^[17]
        
        †Equus major
        
        †Equus giganteus
        
        †Equus pectinatus
        
        †Equus crenidens
        
        Genus †Cremohipparion
        
        Genus †Hippidion
        
        Genus †Pliohippus

Notes

^ Although the plains and mountain zebras have been placed in Hippotigris and Grévy's zebra in Dolichohippus, Vilstrup et al. (2013) finds that the plains zebra and Grévy's zebra are more closely related.^[13] Groves and Bell (2004) place all three species in the subgenus Hippotigris.^[14]

References

^ "PBDB". Paleobiology Database. Retrieved 2021-07-18.
^ Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 255. ISBN 1-84028-152-9.
^ Engels, Sandra; Schultz, Julia A. (June 2019). "Evolution of the power stroke in early Equoidea (Perissodactyla, Mammalia)". Palaeobiodiversity and Palaeoenvironments. 99 (2): 271–291. Bibcode:2019PdPe...99..271E. doi:10.1007/s12549-018-0341-4. ISSN 1867-1594. S2CID 133808650.
^ Janis, Christine (1976). "The Evolutionary Strategy of the Equidae and the Origins of Rumen and Cecal Digestion". Evolution. 30 (4): 757–774. doi:10.1111/j.1558-5646.1976.tb00957.x. ISSN 1558-5646. PMID 28563331. S2CID 5053639.
^ Cantalapiedra, Juan L.; Sanisdro, Oscar L.; Cantero, Enrique; Prado, Jose Luis; Alberdi, Mª Teresa Luis (4 August 2023). "Evolutionary Radiation of Equids". In Prins, Herbert H.; Gordon, Ian J. (eds.). The Equids, A Suite of Splendid Species. Fascinating Life Sciences. Springer. pp. 27–45. doi:10.1007/978-3-031-27144-1_2. ISBN 978-3-031-27143-4 – via www.springer.com.
^ MacFadden, B. J. (March 18, 2005). "Fossil Horses--Evidence for Evolution" (PDF). Science. 307 (5716): 1728–1730. doi:10.1126/science.1105458. PMID 15774746. S2CID 19876380.
^ Savage, RJG & Long, MR (1986). Mammal Evolution: an illustrated guide. New York: Facts on File. pp. 200–204. ISBN 0-8160-1194-X.
^ ^a ^b Froehlich, D.J. (February 2002). "Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla)". Zoological Journal of the Linnean Society. 134 (2): 141–256. doi:10.1046/j.1096-3642.2002.00005.x.
^ Hay, Oliver P. (1915). "Contributions to the Knowledge of the Mammals of the Pleistocene of North America". Proceedings of the United States National Museum. 48 (2086): 535–549. doi:10.5479/si.00963801.48-2086.515
^ ^a ^b Bravo-Cuevas, V.M.; Ferrusquía-Villafranca, I. (2010). "The oldest record of Equini (Mammalia: Equidae) from Mexico" (PDF). Revista Mexicana de Ciencias Geológicas. 27 (3): 593–603. Retrieved 14 August 2020.
^ Aouraghe, Hassan; et al. (1999). "Les équidés du Pléstocène supérior de la grotte Zouhrah à El Harhoura, Maroc". Quaternaire (in French). 10: 283–292. doi:10.3406/quate.1999.1649.
^ Orlando, L.; et al. (2008). "Ancient DNA Clarifies the Evolutionary History of American Late Pleistocene Equids". Journal of Molecular Evolution. 66 (5): 533–538. Bibcode:2008JMolE..66..533O. doi:10.1007/s00239-008-9100-x. PMID 18398561. S2CID 19069554.
^ Vilstrup, Julia T.; et al. (2013). "Mitochondrial Phylogenomics of Modern and Ancient Equids". PLOS ONE. 8 (2): e55950. Bibcode:2013PLoSO...855950V. doi:10.1371/journal.pone.0055950. PMC 3577844. PMID 23437078.
^ Groves, C. P.; Bell, C. H. (2004). "New investigations on the taxonomy of the zebras genus Equus, subgenus Hippotigris". Mammalian Biology. 69 (3): 182–196. Bibcode:2004MamBi..69..182G. doi:10.1078/1616-5047-00133.
^ Eisenmann, Vera (March 2010). "Sussemionus, a new subgenus of Equus (Perissodactyla, Mammalia)". Comptes Rendus Biologies. 333 (3): 235–240. doi:10.1016/j.crvi.2009.12.013. PMID 20338542.
^ Eisenmann, Vera; Vasilijiev, Sergej (September 2011). "Unexpected finding of a new Equus species (Mammalia, Perissodactyla) belonging to a supposedly extinct subgenus in late Pleistocene deposits of Khakassia (Southwestern Siberia)". Geodiversitas. 33 (3): 519–530. doi:10.5252/g2011n3a5. S2CID 128625427.
^ "Fossilworks: Equus fraternus". fossilworks.org. Retrieved 17 December 2021.

[15] Although the plains and mountain zebras have been placed in Hippotigris and Grévy's zebra in Dolichohippus, Vilstrup et al. (2013) finds that the plains zebra and Grévy's zebra are more closely related.^[13] Groves and Bell (2004) place all three species in the subgenus Hippotigris.^[14]

[1] "PBDB". Paleobiology Database. Retrieved 2021-07-18.

[2] Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 255. ISBN 1-84028-152-9.

[3] Engels, Sandra; Schultz, Julia A. (June 2019). "Evolution of the power stroke in early Equoidea (Perissodactyla, Mammalia)". Palaeobiodiversity and Palaeoenvironments. 99 (2): 271–291. Bibcode:2019PdPe...99..271E. doi:10.1007/s12549-018-0341-4. ISSN 1867-1594. S2CID 133808650.

[4] Janis, Christine (1976). "The Evolutionary Strategy of the Equidae and the Origins of Rumen and Cecal Digestion". Evolution. 30 (4): 757–774. doi:10.1111/j.1558-5646.1976.tb00957.x. ISSN 1558-5646. PMID 28563331. S2CID 5053639.

[5] Cantalapiedra, Juan L.; Sanisdro, Oscar L.; Cantero, Enrique; Prado, Jose Luis; Alberdi, Mª Teresa Luis (4 August 2023). "Evolutionary Radiation of Equids". In Prins, Herbert H.; Gordon, Ian J. (eds.). The Equids, A Suite of Splendid Species. Fascinating Life Sciences. Springer. pp. 27–45. doi:10.1007/978-3-031-27144-1_2. ISBN 978-3-031-27143-4 – via www.springer.com.

[6] MacFadden, B. J. (March 18, 2005). "Fossil Horses--Evidence for Evolution" (PDF). Science. 307 (5716): 1728–1730. doi:10.1126/science.1105458. PMID 15774746. S2CID 19876380.

[MamEv-7] Savage, RJG & Long, MR (1986). Mammal Evolution: an illustrated guide. New York: Facts on File. pp. 200–204. ISBN 0-8160-1194-X.

[Froehlich2002-8] Froehlich, D.J. (February 2002). "Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla)". Zoological Journal of the Linnean Society. 134 (2): 141–256. doi:10.1046/j.1096-3642.2002.00005.x.

[9] Hay, Oliver P. (1915). "Contributions to the Knowledge of the Mammals of the Pleistocene of North America". Proceedings of the United States National Museum. 48 (2086): 535–549. doi:10.5479/si.00963801.48-2086.515

[Bravo2010-10] Bravo-Cuevas, V.M.; Ferrusquía-Villafranca, I. (2010). "The oldest record of Equini (Mammalia: Equidae) from Mexico" (PDF). Revista Mexicana de Ciencias Geológicas. 27 (3): 593–603. Retrieved 14 August 2020.

[11] Aouraghe, Hassan; et al. (1999). "Les équidés du Pléstocène supérior de la grotte Zouhrah à El Harhoura, Maroc". Quaternaire (in French). 10: 283–292. doi:10.3406/quate.1999.1649.

[AncientDNA-12] Orlando, L.; et al. (2008). "Ancient DNA Clarifies the Evolutionary History of American Late Pleistocene Equids". Journal of Molecular Evolution. 66 (5): 533–538. Bibcode:2008JMolE..66..533O. doi:10.1007/s00239-008-9100-x. PMID 18398561. S2CID 19069554.

[Vilstrup-13] Vilstrup, Julia T.; et al. (2013). "Mitochondrial Phylogenomics of Modern and Ancient Equids". PLOS ONE. 8 (2): e55950. Bibcode:2013PLoSO...855950V. doi:10.1371/journal.pone.0055950. PMC 3577844. PMID 23437078.

[GrovesBell2004-14] Groves, C. P.; Bell, C. H. (2004). "New investigations on the taxonomy of the zebras genus Equus, subgenus Hippotigris". Mammalian Biology. 69 (3): 182–196. Bibcode:2004MamBi..69..182G. doi:10.1078/1616-5047-00133.

[16] Eisenmann, Vera (March 2010). "Sussemionus, a new subgenus of Equus (Perissodactyla, Mammalia)". Comptes Rendus Biologies. 333 (3): 235–240. doi:10.1016/j.crvi.2009.12.013. PMID 20338542.

[17] Eisenmann, Vera; Vasilijiev, Sergej (September 2011). "Unexpected finding of a new Equus species (Mammalia, Perissodactyla) belonging to a supposedly extinct subgenus in late Pleistocene deposits of Khakassia (Southwestern Siberia)". Geodiversitas. 33 (3): 519–530. doi:10.5252/g2011n3a5. S2CID 128625427.

[18] "Fossilworks: Equus fraternus". fossilworks.org. Retrieved 17 December 2021.

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