Horsin’ Around 8-24-09
August 24, 2009
Eohippus (“dawn horse”) is the scientific name for this creature about the size of a terrier (dog). This creature originated about 50 million years ago, as science points out. But there were no horses on the continent when Columbus arrived in 1492. Although there have been well preserved fossilized remains found in riverbeds clays and sandy, arid regions on the western United States.
Called the Equidae it is a mammalian family comprising the single genus Equus, consisting of all domestic and feral horses, donkeys, zebras, and onagers. Evolution of the family is well-documented and certain distinct physical and mental characteristics of the modern horse can be traced back to its early ancestors. Eohippus was physically different from modern Equus (horse). Its legs were long and thin, meant for running and ending in four toes in front and three behind. The teeth were the wrong shape and too soft for eating grass. Its teeth and short neck indicated that Eohippus fed on succulent leaves that flourished in the subtropical climate of 60 to 40 million years B.C.
According to science the Eohippus lasted about 15 million years before being replaced with the Mesohippus. This animal stood at about 20 inches with striking adaptive changes. It had only three toes on each foot. However, the middle toe was the largest of the three, although all three toes touched the ground. In addition, the spinal column was more nearly horizontal and the legs were longer and thinner with muscles concentrated in the upper parts, close to the body. This indicated that Mesohippus depended on running long distances rather than merely leaping and dashing undercover to flee enemies. Within its more elongated, horse like skull resided a larger brain, which received visual stimuli from eyes placed farther apart. The Mesohippus’ neck was longer than Eohippus, but still contained soft teeth indicating it had not yet made the switch from browser to grazer.
According to scientific study, due to climatic changes, the Mesohippus and other strains of horses developed and migrated from North America to Europe, and as persistent flooding occurred lush jungle habitats gave way to grassy plains. In response the Merychippus developed with teeth suitable for grinding the abundant but tough grasses of the rolling plains. These new, enamel reinforced teeth continued to grow throughout the life of the horse until now.
Merychippus was about 35 inches at the withers and spinal column changes which finally raised the forehand higher than the quarters, as is true in the modern horse. The legs were further-modified for speed. The sideways movement of the leg joint at the radius and ulna in the front of the leg, and tibia fibula behind ended. These evolvements allowed for high speed in one direction for escape, forward and reverse. Although Merychippus still possessed three toes, only the middle toe touched the ground.
* Note: The information in this article is based on information from the text book “Horses: A Practical and Scientific Approach” written by Melvin Bradley.
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Prior to his retirement, Roger Thompson was a CHA certified instructor of advanced Western horsemanship and beginning English riding.