Equids.
Abstract: Alongside domestic horses and donkeys, the horse family, also known as equids, comprises six extant wild species of asses and zebras (Figure 1). Equids are extremely well represented in the fossil record, comprising a 55 million-year evolutionary history, punctuated by many episodes of innovation, extinction and migration. Limited to the single genus Equus today, in the Miocene (23.0–5.3 million years ago) the equid family flourished, comprising more than twenty genera. The group originated in Northern America, where the earliest fossil forms have been found, the so-called Hyracotheres, no larger than small dogs. These animals were soft-leaf browsers and in contrast to modern equids, which roam on a single toe with a solid keratin hoof, their hindlimbs were three-toed and their forelimbs four-toed. Equids thus form, together with rhinos and tapirs, the perissodactyls, an order of mammals characterized by an odd number of toes. Unlike ruminants, they are hindgut fermenters, which digest plant cellulose in their intestines and not in differentiated multiple stomach chambers.
Publication Date: 2015-10-21 PubMed ID: 26485367DOI: 10.1016/j.cub.2015.09.005Google 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.
- Journal Article
Summary
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The research article provides an overview of the horse family, or equids, which include both domestic and wild species, detailing their evolution, anatomical changes, and dietary habits over a 55-million-year period.
Evolutionary History of Equids
- The article provides a comprehensive view of the equid family’s evolutionary journey spanning 55 million years. This journey is marked by significant events such as innovation, extinction, and migration.
- The equids, although limited to the single genus Equus today, were considerably more diverse in the Miocene era (23.0-5.3 million years ago). During this period, the equid family comprised over twenty different genera.
- The study also identifies North America as the origin point for equids, as the earliest fossil forms, known as Hyracotheres, are found here. These first equids were not bigger than small dogs.
Anatomical Changes
- Initial equids, the Hyracotheres, had a different physical structure compared to modern equids. They were browsers, feeding mostly on soft leaves.
- An interesting contrast between early and current equids is the number of toes. The forelimbs of early equids were four-toed, and their hindlimbs were three-toed. By contrast, modern equids walk on a single toe capped by a solid keratin hoof.
- This feature links equids with other species such as rhinos and tapirs, who together form the perissodactyls, a mammal order characterized by having an odd number of toes on each foot.
Dietary Habits
- Equids are unique when compared to ruminants in terms of their digestive process.
- While ruminants have specialized multiple stomach chambers to digest plant cellulose, equids are hindgut fermenters. They carry out the digestion of cellulose in their intestines.
Cite This Article
APA
Orlando L.
(2015).
Equids.
Curr Biol, 25(20), R973-R978.
https://doi.org/10.1016/j.cub.2015.09.005 Publication
Researcher Affiliations
- Centre for GeoGenetics, Natural History Museum of Denmark, Øster Voldgade 5-7, 1350K Copenhagen, Denmark. Electronic address: Lorlando@snm.ku.dk.
MeSH Terms
- Animals
- Animals, Domestic / genetics
- Animals, Domestic / physiology
- Biological Evolution
- Conservation of Natural Resources
- Equidae / genetics
- Equidae / physiology
- Extinction, Biological
- Genome
Citations
This article has been cited 13 times.- Batcher K, Varney S, Raudsepp T, Jevit M, Dickinson P, Jagannathan V, Leeb T, Bannasch D. Ancient segmentally duplicated LCORL retrocopies in equids. PLoS One 2023;18(6):e0286861.
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- Bao W, Yu J, He Y, Liu M, Yang X. The diversity analysis and gene function prediction of intestinal bacteria in three equine species. Front Microbiol 2022;13:973828.
- Tan X, He Y, Qin Y, Yan Z, Chen J, Zhao R, Zhou S, Irwin DM, Li B, Zhang S. Comparative analysis of differentially abundant proteins between high and low intramuscular fat content groups in donkeys. Front Vet Sci 2022;9:951168.
- Norris SL, Little HA, Ryding J, Raw Z. Global donkey and mule populations: Figures and trends. PLoS One 2021;16(2):e0247830.
- Gambini A, Duque Rodríguez M, Rodríguez MB, Briski O, Flores Bragulat AP, Demergassi N, Losinno L, Salamone DF. Horse ooplasm supports in vitro preimplantation development of zebra ICSI and SCNT embryos without compromising YAP1 and SOX2 expression pattern. PLoS One 2020;15(9):e0238948.
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- Nacarino-Meneses C, Jordana X, Orlandi-Oliveras G, Köhler M. Reconstructing molar growth from enamel histology in extant and extinct Equus. Sci Rep 2017 Nov 21;7(1):15965.
- Nacarino-Meneses C, Jordana X, Köhler M. Histological variability in the limb bones of the Asiatic wild ass and its significance for life history inferences. PeerJ 2016;4:e2580.
- Ali M. Tibetan wild ass, Equus kiang, in the literature: a comprehensive review. J Equine Sci 2025;36(4):115-127.
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