Evolution of the horse in the context of "Paleocene"

The horse (Equus ferus caballus) is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of Equus ferus. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature, Eohippus, into the large single-toed animal of today, originally in North America. Humans began domesticating horses around 4000 BCE in Central Asia, and their domestication is believed to have been widespread by 3000 BCE. Horses in the subspecies caballus are domesticated, although some domesticated populations live in the wild as feral horses. These feral populations are not true wild horses, which are horses that have never been domesticated. There is an extensive, specialized vocabulary used to describe equine-related concepts, covering everything from anatomy to life stages, size, colors, markings, breeds, locomotion, and behavior.

Horses are adapted to run, allowing them to quickly escape predators, and possess a good sense of balance and a strong fight-or-flight response. Related to this need to flee from predators in the wild is an unusual trait: horses are able to sleep both standing up and lying down, with younger horses tending to sleep significantly more than adults. Female horses, called mares, carry their young for approximately 11 months and a young horse, called a foal, can stand and run shortly following birth. Most domesticated horses begin training under a saddle or in a harness between the ages of two and four. They reach full adult development by age five, and have an average lifespan of between 25 and 30 years.

George Gaylord Simpson (June 16, 1902 – October 6, 1984) was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern synthesis, contributing Tempo and Mode in Evolution (1944), The Meaning of Evolution (1949) and The Major Features of Evolution (1953). He was an expert on extinct mammals and their intercontinental migrations. Simpson was extraordinarily knowledgeable about Mesozoic fossil mammals and fossil mammals of North and South America. He anticipated such concepts as punctuated equilibrium (in Tempo and Mode) and dispelled the myth that the evolution of the horse was a linear process culminating in the modern Equus caballus. He coined the word hypodigm in 1940, and published extensively on the taxonomy of fossil and extant mammals. Simpson was influentially, and incorrectly, opposed to Alfred Wegener's theory of continental drift, but accepted the theory of plate tectonics (and continental drift) when the evidence became conclusive.

He was Professor of Zoology at Columbia University, and Curator of the Department of Geology and Paleontology at the American Museum of Natural History from 1945 to 1959. He was Curator of the Museum of Comparative Zoology at Harvard University from 1959 to 1970, and a Professor of Geosciences at the University of Arizona from 1968 until his retirement in 1982.