Fossil Horses:

Othniel Charles Marsh's Proof for Darwin's Theory of Evolution

When Charles Darwin published his Origin of Species in 1859, there was not much evidence that supported the theory of evolution and its mechanism of natural selection. While Darwin observed variation, such as the finches on the Galápagos, there was no direct evidence available at the time to show development through the ages; nothing to show how animals (including humans) evolved. It wasn't until Othniel Charles Marsh discovered fossil records of extinct horses that Darwin's theory was taken seriously.

Othniel Charles Marsh, born in Lockport, New York, on October 29, 1831, developed a love for the outdoors at an early age. He also had associated himself with the geologist Colonel Ezekial Jewett. It was when Marsh discovered some small halibut fossils while looking for minerals to add to his collection that he first became aware of fossils. Though he wasn't interested in the fossils at the time, Marsh attended school where he met Louis Agassiz who became excited about Marsh's fossils. He described them as looking like they belonged to an animal that hadn't been seen before - a combination between fish and reptile. However, Marsh convinced Agassiz that he was wrong about the fossils and then went on to publish a paper about them seven years after the discovery, naming the fossil Eosaurus acadianus. With this paper, Marsh established himself as a promising paleontologist. He later became a professor at Yale - the first professor in paleontology in America and only the second in the world in 1866. However, the discovery that would make him famous, as well as show Darwin's theory to be correct, had yet been made.

While traveling West in 1868, Marsh heard reports of "human remains" at the bottom of a well at Antelope Station, Nebraska. He was skeptical, but upon viewing them, he could clearly see that they were from ancient equines. He had the conductor save some for his return back East. When Marsh examined the bones, he determined that they had come from an animal from Pliocene times that was barely a yard in height and had long slender legs which ended with three toes on each foot. He dubbed the small horse Equus parvulus (now Protohippus). It would later be one of the "missing links" in understanding the genealogy of modern Equus. Subsequent expeditions out West with his students from Yale and often military escorts followed in the early 1870's. By the mid-1870's, Marsh had an exceptional collection of early mammals. A large percentage of those were equine, as they were abundant in the region of Nebraska and the Dakotas. In a paper published in 1874 in American Naturalist, Marsh describes some of the horse fossils he found on an expedition in Wyoming and Utah. One of these skeletons, he named Eohippus, or "the dawn horse." However, instead of using Eohippus in this paper, he used Orohippus, as the former hadn't yet been described. The different skeletons had different

Figure 1. a. Orohippus (Eocene); b. Miohippus (Miocene); c. Hipparion (Pliocene); d. Equus (Quaternary)
Follow this by examining the reduction and loss of metacarpal V (red) and its digits (fingers).
Do this likewise for metacarpals II (orange) and IV (green). Note that no horse ever had a thumb (I).

numbers of toes and different degrees of variation, which would eventually be Marsh's main proof of development. He believed that the correct line of descent was Orohippus, Miohippus and Anchitherium, Anchippus, Hipparion, Protohippus and Pliohippus, and Equus, the most recent. The way Marsh determined the line of descent was mostly by examining the metacarpal bones of the different horses. Orohippus (the next horse after Eohippus) had four main digits: metacarpals II through V (the I being used for thumbs, which horses do not have). After looking at the bones from Orohippus, from the Eocene, Marsh looked at the other horses that came afterward. The later the horse was from, the shorter the metacarpal bones V, IV, and II became. He compared what he found to the legs of modern Equus, and found remnants of digits IV and II along the cannon bones (this is more evident in the forefeet that hind). (See Figure 1.d.) Marsh also examined the forearms, legs, as well as and upper and lower molars to confirm what he thought was the right line of descent. From his examinations, he found that through time as the horse evolved to be a larger and faster animal, the forearms and legs became stronger to support the weight (a horse's leg in phases of the gallop has to support its entire weight). The molars evolved from browsing teeth to teeth for a grazing animal - such as today's horse.

The evidence so strongly proved Marsh's theory for horse evolution that even Thomas Henry Huxley, known as an ardent advocate of evolution, was taken with Marsh's collection of fossils and his findings. Marsh recalled, that after seeing the Yale collection, Huxley believed that these specimens "demonstrated the evolution of the horse beyond question, and for the first time indicated the direct line of descent of an existing animal," as quoted from MacFadden, 31. Charles Darwin himself at one point expressed a desire to travel to America for the sole purpose of seeing Marsh's collection at Yale. Though Marsh collected specimens from many species of animals, some extinct and some whose descendents exist today, no other collection of fossils showed a direct line of descent as those from the family Equidae. This evidence probably convinced many people in Marsh's time to support evolutionary naturalism, which is to believe that our traits evolved through natural means. There was renewed interest in Darwin's theory of evolution, though the notion of Lamarckism was still popular. Lamarckian ideas are the beliefs that animals evolved features through use and disuse, not natural selection. Edward D. Cope tried to promote neo-Lamarckian ideas of acquired characteristics, but eventually, people adopted Darwinian ideas - especially after a mechanism for variation was discovered by Hugo de Vries, mutation that led to alterations of characteristics. Marsh's work with the horses made him one of the most prominent paleontologists in 1870's till his death in 1899.

With the help of O.C. Marsh, Charles Darwin's theories presented in his Origin of Species became recognized as being truth. The fact that larger faster horses were better able to survive than small slower many-toed horses supported the idea of natural selection as well as survival of the fittest. Marsh's evidence was in the fossil horses in his collection - the changing bone structure through the ages to support a changing environment and to better adapt for survival from predators. Though Marsh examined many different species of animals in his lifetime, it is his work with the line of descent of the horse that he is recognized with, as well as his vast fossil collection which he donated to Yale. He is also recognized as the first professor of paleontology in America, the second in the world, also adding to Yale's prestige.

To Yale he gave his services, his collections, and his estate.

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