Equus simplicidens, also known as the Hagerman horse is an extinct species of equine native to North America during the Pliocene and Early Pleistocene.[1] It is one of the oldest and most primitive members of the genus Equus. It is the state fossil of Idaho, where abundant remains of the species were discovered near the town of Hagerman in 1928.
| Hagerman horse Temporal range:
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| Mounted skeleton of a Hagerman horse | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Perissodactyla |
| Family: | Equidae |
| Genus: | Equus |
| Species: | †E. simplicidens
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| Binomial name | |
| †Equus simplicidens | |
| Synonyms | |
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Discovery
editA cattle rancher named Elmer Cook discovered some fossil bones on this land in Hagerman, Idaho. In 1928, he showed them to Dr. H. T. Stearns of the U.S. Geological Survey who then passed them on to Dr. James W. Gidley at the Smithsonian Institution. Identified as bones belonging to an extinct horse, the area where the fossils were discovered, called the Hagerman Horse Quarry, was excavated and three tons of specimens were sent back to the Smithsonian in Washington, D.C.[4]
Excavation of the fossils continued into the early 1930s. The Hagerman Horse Quarry floor grew to 5,000 square feet (460 m2) with a backwall 45 feet (14 m) high. Ultimately five nearly complete skeletons, more than 100 skulls, and forty-eight lower jaws as well as numerous isolated bones were found.[4] Gidley believed that such a large amount of fossils found in one location was because of the quarry area being a watering hole at one point. The waterhole could have been where the bones of the Hagerman horses accumulated as injured, old, and ill animals, drawn to water, died there.[4] A study by H. Gregory McDonald in 1996 alternatively suggested based on the age distribution of remains at the quarry, which span from newborns to adults, that a herd died in a single catastrophic event, perhaps attempting to cross a swelled/flooded river.[5]
Classification
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The Hagerman horse was given the scientific name of Plesippus shoshonensis in 1930 by a Smithsonian paleontologist named James W. Gidley[3] who led the initial excavations at Hagerman that same year.
However further study by other paleontologists determined that fossils closely resembled fossils of a primitive horse from Texas named Equus simplicidens, named by paleontologist Edward Drinker Cope in 1892. Because of this similarity, the two forms were interpreted[6] to be the same species, and since the name Equus simplicidens was the older name, it was retained following the taxonomic Principle of Priority. The Hagerman fossils represent some of the oldest widely accepted remains of the genus Equus.[7]
The genus placement of the species is controversial, with some authors choosing to place the species in Plesippus instead.[8] A 2019 phylogenetic analysis found it to be more closely related to living Equus than to Hippidion or Dinohippus, but outside the group containing all living equines.[9]
Evolution
editThe earliest remains of Equus simplicidens date to the Pliocene, around 4.1-3.2 millon years years ago.[10][11] Equus simplicidens has been suggested to be the ancestor of the Eurasian "stenonine" equines such as Equus stenonis, which first appeared in Eurasia at the beginning of the Pleistocene, around 2.6 million years ago, which have been proposed to be the ancestors of living zebras and asses.[7][10] The youngest fossils of E. simplicidens date to the Irvingtonian.[12]
Description
editThe body mass of adult Equus simplicidens been estimated at around 300–400 kilograms (660–880 lb) in life, comparable to a zebra.[10] The overall form of the skull has been considered comparable to those of zebras, though the dental morphology is more primitive.[12] The vomer bone of the skull is noticeably elongate, with the preorbital fossa being relatively large. The ramus of the mandible is angled posteriorly.[7]
Distribution
editRemains of Equus simplicidens are known from across Western and Central North Amerrica, including Idaho, Arizona, California, Texas, Nebraska and Kansas, southwards to Mexico.[12]
Ecology
editEquus simplicidens is thought to have had a highly abrasive almost exclusively grazing based diet, similar to that of modern equines, particularly zebras.[10][13] The species is suggested to have had a herding social structure similar to living Equus, perhaps lead by a dominant harem stallion male similar to living horses.[5]
See also
editReferences
edit- ^ a b Skinner, M.F. (1972). "Order Perissodactyla". In Skinner, M.F.; Hibbard, C.W. (eds.). Early Pleistocene Preglacial and Glacial Rocks and Faunas of North-Central Nebraska. Vol. 148. New York: American Museum of Natural History. pp. 117–125. S2CID 129067309.
- ^ Cope, E. D. (1892). "A Contribution to the Vertebrate Paleontology of Texas". Proceedings of the American Philosophical Society. 30 (137): 124–125. JSTOR 983215.
- ^ a b J.W. Gidley (1930) A new Pliocene horse from Idaho. Journal of Mammalogy 11: 300-303 JSTOR 1374150 doi:10.2307/1374150
- ^ a b c McDonald, H. Gregory (October 1993). "More Than Just Horses Hagerman Fossil Beds: Hagerman, Idaho". Rocks & Minerals. 68 (5): 322–326. doi:10.1080/00357529.1993.9926562. ISSN 0035-7529.
- ^ a b McDonald, H. Gregory (1996-12-31), "Population structure of the late Pliocene (Blancan) zebra Equus simplicidens (Perissodactyla: Equidae) from the Hagerman Horse Quarry, Idaho", Palaeoecology and Palaeoenvironments of Late Cenozoic Mammals, University of Toronto Press, pp. 134–155, doi:10.3138/9781487574154-010, ISBN 978-1-4875-7415-4, retrieved 2024-12-17
- ^ D.E. Savage (1951) late Cenozoic vertebrates of the San Francisco Bay region. University of California Bulletin of the Department of Geological Sciences 28: 215-314
- ^ a b c Cirilli, Omar; Pandolfi, Luca; Rook, Lorenzo; Bernor, Raymond L. (2021-05-12). "Evolution of Old World Equus and origin of the zebra-ass clade". Scientific Reports. 11 (1): 10156. Bibcode:2021NatSR..1110156C. doi:10.1038/s41598-021-89440-9. ISSN 2045-2322. PMC 8114910. PMID 33980921.
- ^ Orlando, Ludovic; Ginolhac, Aurélien; Zhang, Guojie; Froese, Duane; Albrechtsen, Anders; Stiller, Mathias; Schubert, Mikkel; Cappellini, Enrico; Petersen, Bent; Moltke, Ida; Johnson, Philip L. F.; Fumagalli, Matteo; Vilstrup, Julia T.; Raghavan, Maanasa; Korneliussen, Thorfinn (2013-07-04). "Recalibrating Equus evolution using the genome sequence of an early Middle Pleistocene horse". Nature. 499 (7456): 74–78. Bibcode:2013Natur.499...74O. doi:10.1038/nature12323. ISSN 0028-0836. PMID 23803765. S2CID 4318227.
- ^ Cirilli, Omar; Pandolfi, Luca; Rook, Lorenzo; Bernor, Raymond L. (2021-05-12). "Evolution of Old World Equus and origin of the zebra-ass clade". Scientific Reports. 11 (1): 10156. Bibcode:2021NatSR..1110156C. doi:10.1038/s41598-021-89440-9. ISSN 2045-2322. PMC 8114910. PMID 33980921.
- ^ a b c d Cirilli, Omar; Semprebon, Gina M.; Bernor, Raymond L. (September 2024). "Paleodietary reconstruction of Equus simplicidens from the Hagerman Horse Quarry (Idaho, USA) highlights high abrasive habits in North American fossil equids during the Pliocene". Palaeogeography, Palaeoclimatology, Palaeoecology. 650: 112376. Bibcode:2024PPP...65012376C. doi:10.1016/j.palaeo.2024.112376.
- ^ Rook, Lorenzo; Bernor, Raymond L.; Avilla, Leonardo S.; Cirilli, Omar; Flynn, Lawrence; Jukar, Advait; Sanders, William; Scott, Eric; Wang, Xiaoming (2019-07-25). "Mammal Biochronology (Land Mammal Ages) Around the World From Late Miocene to Middle Pleistocene and Major Events in Horse Evolutionary History". Frontiers in Ecology and Evolution. 7. doi:10.3389/fevo.2019.00278. hdl:2158/1168180. ISSN 2296-701X.
- ^ a b c Cirilli, Omar; Machado, Helena; Arroyo-Cabrales, Joaquin; Barrón-Ortiz, Christina I.; Davis, Edward; Jass, Christopher N.; Jukar, Advait M.; Landry, Zoe; Marín-Leyva, Alejandro H.; Pandolfi, Luca; Pushkina, Diana; Rook, Lorenzo; Saarinen, Juha; Scott, Eric; Semprebon, Gina (24 August 2022). "Evolution of the Family Equidae, Subfamily Equinae, in North, Central and South America, Eurasia and Africa during the Plio-Pleistocene". Biology. 11 (9): 1258. doi:10.3390/biology11091258. ISSN 2079-7737. PMC 9495906. PMID 36138737.
- ^ Semprebon, Gina M.; Rivals, Florent; Solounias, Nikos; Hulbert, Richard C. (January 2016). "Paleodietary reconstruction of fossil horses from the Eocene through Pleistocene of North America". Palaeogeography, Palaeoclimatology, Palaeoecology. 442: 110–127. Bibcode:2016PPP...442..110S. doi:10.1016/j.palaeo.2015.11.004.
Further reading
edit- Boss, N. H. "Explorations for Fossil Horses in Idaho". Explorations and Field Work of the Smithsonian Institution in 1931. 1932.
- Gazin, C. L. '" Study of the Fossil Horse Remains from the Upper Pliocene of Idaho. Proceedings from the United States National Museum 83(2,985): 281-320. 1936.
- MacFadden, Bruce J. Fossil Horses: Systematics, Paleobiology and Evolution of the Family Equidae. Cambridge Univ. Press, 1992.
- McDonald, H. Gregory. "More than Just Horses", Rocks and Minerals, September/October 1993. Vol. 68:322-326.
- Willoughby, David P. The Empire of Equus. A.S. Barnes and Co., 1974
- Castle Rock Ranch – Hagerman Horse Quarry Land Exchange Environmental Assessment
External links
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