Evolution of the horse

The evolutionary history of horses, from small, multi-toed early ancestors to modern single-toed members of the genus Equus. It includes branching lineages, changing habitats, and adaptations in teeth and limbs.

Hypsodonty: The condition of having high-crowned teeth adapted to prolonged wear. High-crowned teeth evolved in several horse lineages as abrasive diets and gritty habitats spread.
Hyracotherium: An extinct early equid genus known from Eocene fossils, traditionally associated with the earliest horse evolution. Its small-bodied fossils illustrate the early stage of the horse lineage.
Fossil: Preserved remains, traces, or impressions of organisms from the geological past. Fossils provide the principal evidence for extinct horse forms and their sequence.
Great American Biotic Interchange: The exchange of terrestrial animals between North and South America after the continents became connected. Equids dispersed into South America during this major episode of mammal migration.
Cursoriality: Adaptation for sustained, efficient running, typically involving limb and body specializations. Longer limbs and reduced side toes accompanied increasingly efficient running in many horse lineages.
Orohippus: An extinct Eocene equid genus that lived in North America. It represents an early branch in the succession of fossil equids.
Stratigraphy: The study of rock layers and their order, composition, and age relationships. Rock-layer positions help establish when fossil horse species lived.
Quaternary extinction event: The late-Pleistocene loss of many large mammals across much of the world. Native horse lineages disappeared from the Americas during the late-Pleistocene extinctions.
Grassland: An ecosystem dominated by grasses, with few trees and shrubs. Expanding grasslands altered food and habitat conditions for later horses.
Mesohippus: An extinct Oligocene equid genus with three toes on each foot. Its fossils show a later small horse with a more developed middle toe.

Linked from 6 pages