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Ancient Horse (Equus cf. E. complicatus)

jefferson and horse

In his 1807 expedition to collect "Mammoth" (American mastodon) fossils at Big Bone Lick, William Clark also collected the fossils of several other large mammals. Among these, reported Clark, were "leg and foot bones of the Horses" (1).

Neither Thomas Jefferson, who received these fossils, nor Caspar Wistar, the anatomist who evaluated them, commented on the horse fossils. Their lack of comment is interesting given the conventional wisdom was that the first horses to appear in the Americas were brought there by the Spanish Conquistadors (2). Subsequent accounts of fossil horses in the Americas were generally dismissed until 1848, when Richard Owen described a fossil horse from South America. He named the fossils Equus curvidens (3).

The first scientific paper on North American horses was also written in 1848. The author, Joseph Leidy (4), reported on horse fossils from three localities. The first was a set of fossil teeth that was collected from Big Bone Lick sometime after the Clark/Jefferson expedition (5). The second was another set of fossil teeth from Natchez, Mississippi. The third was a single tooth from Georgia.

fossil horse teeth
Views from the side (top) &
chewing surfaces (bottom) of two
molars from Equus complicatus
(after Leidy, 1873)

Teeth are typically the most distinctive and diagnostic fossils for horses, but they also exhibit considerable within-species variability in their anatomical details. Leidy was uncertain whether the teeth from Big Bone Lick were sufficiently different from known species to warrant their designation as a new species. Consequently he attributed the teeth to Owen's Equus curvidens. On the other hand, the teeth from Natchez were distinctive enough to belong to a new species, Equus complicatus (6); Leidy also attributed the Georgia tooth to E. complicatus. Later studies identified the Big Bone Lick teeth of by J. P. Wetherill collection as Equus complicatus; the leg and foot bones collected by Clark are not sufficiently distinctive and cannot be conclusively identified to this or any other species of Equus.

Equus complicatus, also known as the complex-tooth horse, was the most common Pleistocene horse in the eastern and southern parts of the United States. Growing to about the size of the modern species, E. complicatus was a relatively large species. Several other species, including the Mexican horse (Equus conversidens), Scott's horse (Equus scotti), Western horse (Equus occidentalis), and Yukon Horse (Equus lambei) were common elsewhere in North America during the late Pleistocene.

Equus complicatus was the first North American fossil horse to be described, but research conducted by Leidy and others revealed a remarkable diversity of American fossil horses. Indeed, horses actually evolved in North America and dispersed to the Old World via the Bering Land Bridge. While several of the Eurasian and African species are with us today, the last of the native American horses died out about 8,000 years ago.

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Web Pages:

  1. Florida Museum of Natural History's Fossil Horses Cybermuseum:
    www.flmnh.ufl.edu/fhc/firstCM.htm
  2. Page Museum's (La Brea Tarpits) web page on Western Horse:
    www.tarpits.org/education/guide/flora/horse.html
  3. Yukon Beringia's web page on the Yukon Horse:
    www.beringia.com/02/02maina14.html

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Print Resources:

  1. Kurtén, B. and E. Anderson. 1980. Pleistocene Mammals of North America. Columbia University Press. New York. 442 pp.
  2. Lang, I.A. 2002. Ice Age Mammals of North America: A Guide to the Big, the Hairy, and the Bizarre. Missoula: Mounain Press.
  3. Leidy, Joseph. 1848. "On the fossil horse of America". Proceedings of the Academy of Natural Sciences of Philadelphia. 3(11): 262-266.
  4. Leidy, Joseph. 1858. [Remarks on extinct vertebrates of the Niobrara River valley.] Proceedings of the Academy of Natural Sciences of Philadelphia, 10: 10.
  5. Leidy, Joseph . 1873. "Contributions to the extinct vertebrate fauna of the western territories." Report of the United States Geological Survey of the Territories [Hayden Survey]. Volume I. Fossil vertebrates. Part I. Government Printing Office, Washington, 358 pp..
  6. Rice, H.C. Jr. 1951. "Jefferson's Gift of Fossils to the Museum of Natural History in Paris." Proceedings of the American Philsophical Society. 95: 599-610.

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Notes:

  1. In 1807, William Clark (of Lewis and Clark fame) led an expedition to Big Bone Lick, Kentucky to retrieve fossils of the "Mammoth" (American mastodon). Almost all of the specimens in the Thomas Jefferson Fossil Collection came from this expedition. See Discovering the Mastodon: Fossils in the White House for more information. [go back]
  2. Horses were particularly valuable to the Spanish conquests the Aztecs and Incas. Although renown for their military prowess, warriors from these two empires were intimidated by these strange animals and by the men who could master them. Over time, some of the Spanish horses escaped and became successfully established in both Americas. [go back]
  3. Richard Owen (1804-1892) was the leading British anatomist and paleontologist of his time. The fossils of Equus curvidens were collected by Charles Darwin during his famous voyage on the H.M.S. Beagle. (go back]
  4. Joseph Leidy (1823-1891) was a leading paleontologist, zoologist and anatomist during the 19th century. See the Academy's Online Exhibit on Joseph Leidy or see the online exhibit's web page on fossil horses. [go back]
  5. The Big Bone Lick teeth were part of J. P. Wetherill's collection, which included numerous other fossils from Big Bone Lick. The collection was donated to the Academy during the first half of the 19th century. [go back]
  6. Leidy originally named the Natchez horse teeth Equus americanus, but he later learned that this name was preoccupied (i.e., it was already used) so he renamed the species Equus complicatus in reference to the complex folding patterns in the teeth's enamel. [go back]

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