The Annals of Gor. Million Years Ago I Was Taking a Walk! When you have this picture of wildlife in mind you're ready for your journey into the past. Dawn is building a new day and those animals which hunt and feed at night are disappearing into their lairs. It sometimes flooded, and as it spread out over the wide, flat plain it deposited layers of sand and silt that geologists today call the Harrison Formation. The ancient Niobrara and other similar rivers spread the same sediments over nearby areas in eastern Wyoming and southwestern South Dakota. In the sediments, paleontologists would one day find millions of bones. Our ancient river was the center of life for an untold numbers of animals. They lived in it, along its banks, in the willow thickets that grew on its more permanent sandbars, and on the broad, tree- dotted plains that stretched to the horizon beyond the river's normal course. Great herds of small horses, rhinoceroses, camels, and other dwellers on the savanna came to water holes to drink and to wallow in the cool and refreshing pools. Miocene Parahippus Anchitherium Miohippus Oligocene Mesohippus Epihippus Grazing horses. Species that can survive in different kinds of habitats, or. Miohippus evolved from the earlier genus Mesohippus; however. Tips for Editing Leave Edit Mode Submit. We welcome suggested improvements to any of our articles. You can make it easier for us to review and. The evolution of the horse. Miohippus evolved from the earlier genus Mesohippus; however. Tips for Editing Leave Edit Mode Submit. We welcome suggested improvements to any of. We know that in the modern world rhinos belong in Africa and southeastern Asia, not North America, yet this continent was the major home of these strange beasts for millions of years. Rhinos did not become extinct in North America until about 5 million years ago, during the middle Pliocene. Along the ancient Niobrara the rhino herds are not made up of the giant mammals we see in zoos today. The ones we see moving slowly toward the river on this early Miocene day are no larger than big domestic pigs. They are the first among the rhinos to have horns — not one behind the other, but a pair near the end of the nose, side by side. To scientists today these rhinos are known as Menoceras. The name Diceratherium, once used both for these small rhinos and a larger type of ancient rhino, now refers accurately to just the large rhino. You can see that the males have the paired nose horns, and that the females, which are about the same size, do not. Trotting amid the herd are fat little colts whose seriousness of purpose belies their youth. The herd seems to be made up of about forty to fifty (4. Suddenly they are startled by a large cat or dog stalking through the grass, and all the males on the side nearest the enemy bunch together to face the hungry hunter. Most of the herd continues to flow across the plain, and when the danger is past the guardian males catch up in a lumbering gallop. This mural (click on the picture to enlarge) depicts life in the Agate Fossil Beds area in the early Miocene Epoch, about 2. The painting is a composite of life at that time where all of these forms of life might be found together at any given moment. A copy hangs in the visitor center at Agate Fossil Beds National Monument. It is hot today, and the flies are biting even through the tough rhino hides. Many of the adults go into deeper pools to roll and soak while the young drop their serious attitudes and frolic in the shallows. When twilight comes, the herd draws together, colts and females toward the center and bulls around the edges. After a period of milling and pushing, the herd finally beds down for the night, with only the perimeter guards moving around on the edges. The daily routines of the other herds of grass- and leaf- eating animals generally follow somewhat different patterns from that of the rhinos. Of them, only the piglike oreodons wallow in the river. The others spend nearly all their time out on the savanna, coming to the river only at dawn or dusk to drink. Oreodons were among the most abundant medium- sized animals of the middle Tertiary. A strictly North American group, they have been described as looking like a cross between a sheep and a pig. As small as a house cat or as big as a domestic pig, these mammals reached a peak in abundance and variety between the middle Oligocene and the early Miocene (though they are known from the late Eocene through the early Pliocene). This peak probably has never been equalled by any other group of mammals in such a size range. As we stop and look out among the herds of animals dotting the plain, we can see only a few small bands of oreodons. The backs of their cheek bones flare out far to the sides, so that with their narrow snouts they are most peculiar looking. Their bodies are long and rather nondescript, and their legs are short but slender. This particular kind is known as Promerycochoerus (. They are really a rare sight here at our river. Perhaps the large herds of Menoceras fill their ecologic niche locally, and the oreodons have found they cannot successfully compete with the rhinos for food, water, and living space. After all, not everything can fit into Paradise. Now take a look to the northeast: there's a herd of Miohippus (. We should take an especially good look at this herd — they are part of a doomed race! This same circumstance makes the high plains a land of little rain today. In effect, the savannas will give way to prairies. Some evolved into something else. But the end result was the complete termination of the genus Miohippus as paleontologists recognize it. From now on, fleetness of foot will be a most important factor in horse survival. Miohippus will also give rise to somewhat larger forest horses that will survive on into the Pliocene in patches of woodland. They will be little changed except in size (some came to be nearly as large as the modern horse), and some of them will even cross the Bering Land Bridge into Eurasia. This is the last time, however, that we'll see these primitive horses in large numbers here in North America. They seem to be enjoying their mixed diet and thriving on it, so they won't be too badly hurt in the geologically near future when they have to eat mostly grass. For a long time some individuals of Miohippus carried a little extra wrinkle of enamel on the crowns of their upper grinding teeth — and now the wrinkle occurs in all individuals of Parahippus. Because of it, Parahippus can eat grass without wearing out its teeth before reaching breeding age, making it possible for most individuals to reproduce before dying. The little wrinkle is passed on. It's only a small advantage, but such is the stuff that survival and evolution are made of. Parahippus is the forerunner of a vast array of different three- toed, long- limbed prairie horses that will be the most numerous members of their family until nearly the end of the Pliocene. From one of their descendants will come the first one- toed horse — the direct ancestor of our modern horses. There's a group of something very small moving through the tall grass, but it's completely hidden. Only the swaying of the 6. Now they've moved out into an area of cropped grass, and we can see a herd of the diminutive deerlike Nanotragulus (. Not a great deal larger than a house cat, these little . Their ancestry goes back for millions of years into the early Oligocene, when some of their ancestors stood less than 1. But their entire family is soon to become extinct. They are part of the grazing community, although they eat leaves and softer vegetation just as readily. As this group scampers toward the river, we can see that they have a peculiar crouching gait — their forelegs are so much shorter than their hind legs that they seem to be running continuously downhill. They are dainty little animals with small, delicate heads and short, slender limbs. They can bound swiftly away if danger threatens, but they'd rather hide in the thick brush. A few of the females have fawns with them, tiny things less than 1. Look at them all scatter! Young Nanotragulus either learn to duck down at the sight of a passing shadow or they don't get a chance to learn at all. This time they all got away, and the hawk will have to look elsewhere for a meal. They swoop down on the mice and pocket gophers, young rabbits and beavers, baby . All manner of meat- eaters depend on the small animals for food, and the little Nanotragulus are most vulnerable as they move through the canopy of grass. There doesn't seem to be any other herds moving into view just now; but look over there in that patch of short grass is a bird rarely seen in North America anymore. It's a guan, a ground- living bird related to the grouse and sagehens. It must be far from home this morning; most of its time is spent in the thick brush farther back from the river. How much roughage is recommended in horse's diet? What color is a normal horses eye. Cyber Security Tips on how to stay safe online in 2017 by ana. Teeth/Diet: the pliohippus also. The Pliohippus (12 mya - 5 mya) The Parahippus (20 mya - 12 mya). A heavy body and long neck and tail make this animal easy to identify. Let's look at some of the individuals and small groups that are moving or resting within view. We still carry all the genes for making vitamin C but no longer use them, probably because our primate ancestors got it from their fruit-rich diets instead. The camels with the very slender legs and long necks are called Oxydactylus (. They are browsing on the willows where the herd of Nanotragulus ran to hide. Oxydactylus is an important camel, standing about at the midpoint in the evolution of this North American family of mammals. The camels will remain stay- at- homes in the continent of their origin until they spread into Eurasia and South America at the beginning of the Pleistocene Epoch, some 2. Agate. There are many species of Oxydactylus; the one we are looking at stands about 1. Notice that. they don't have humps on their backs; in this lush land there is no need to store fat against a time of possible starvation. Speaking of camels, here comes a herd of Stenomylus (. This is a strange little long- neck camel that strayed off the main line of the family's evolution. Less than 6. 0 centimeters (2. African antelope called the gerenuk. Stenomylus, with its long and delicate legs and tall cheek- teeth, is perfectly adapted for living in and eating the abundant grass which billows on this treedotted plain. Yet many of the little Stenomylus are going to share a tragic time with hundreds of Menoceras only a year or so from this day we are visiting. When you travel back 2. Do you see that hulk stepping out of the shade? At first glance, you might think it's the Dragon of the Ishtar Gate. What a wonderful animal! They don't have hooves; each toe ends in a great curved claw! Evolution of the horse - WOW. This image shows a representative sequence, but should not be construed to represent a . Reconstruction, left forefoot skeleton (third digit emphasized yellow) and longitudinal section of molars of selected prehistoric horses. The evolution of the horse, a mammal of the family Equidae, occurred over a geologic time scale of 5. Paleozoologists have been able to piece together a more complete outline of the evolutionary lineage of the modern horse than of any other animal. The horse belongs to the order Perissodactyla (odd- toed ungulates), the members of which all share hooved feet and an odd number of toes on each foot, as well as mobile upper lips and a similar tooth structure. This means that horses share a common ancestry with tapirs and rhinoceroses. The perissodactyls arose in the late Paleocene, less than 1. Cretaceous. This group of animals appears to have been originally specialized for life in tropical forests, but whereas tapirs and, to some extent, rhinoceroses, retained their jungle specializations, modern horses are adapted to life on drier land, in the much harsher climatic conditions of the steppes. Other species of Equus are adapted to a variety of intermediate conditions. The early ancestors of the modern horse walked on several spread- out toes, an accommodation to life spent walking on the soft, moist grounds of primeval forests. As grass species began to appear and flourish. At the same time, as the steppes began to appear, the horse's predecessors needed to be capable of greater speeds to outrun predators. This was attained through the lengthening of limbs and the lifting of some toes from the ground in such a way that the weight of the body was gradually placed on one of the longest toes, the third. History of research. Wild horses were known since prehistory from central Asia to Europe, with domestic horses and other equids being distributed more widely in the Old World, but no horses or equids of any type were found in the New World when European explorers reached the Americas. When the Spanish colonists brought domestic horses from Europe, beginning in 1. In the 1. 76. 0s, the early naturalist Buffon suggested this was an indication of inferiority of the New World fauna, but later reconsidered this idea. The tooth was sent to the Paris Conservatory, where it was identified by Georges Cuvier, who identified it as a browsing equine related to the tapir. On 1. 0 October 1. Santa Fe, Argentina, he was . A decade later, however, he found the latter name had already been taken and renamed it Equus complicatus. The sequence, from Eohippus to the modern horse (Equus), was popularized by Thomas Huxley and became one of the most widely known examples of a clear evolutionary progression. The horse's evolutionary lineage became a common feature of biology textbooks, and the sequence of transitional fossils was assembled by the American Museum of Natural History into an exhibit that emphasized the gradual, . The straight, direct progression from the former to the latter has been replaced by a more elaborate model with numerous branches in different directions, of which the modern horse is only one of many. George Gaylord Simpson in 1. Although some transitions, such as that of Dinohippus to Equus, were indeed gradual progressions, a number of others, such as that of Epihippus to Mesohippus, were relatively abrupt in geologic time, taking place over only a few million years. Both anagenesis (gradual change in an entire population's gene frequency) and cladogenesis (a population . The change in equids' traits was also not always a . The family lived from the Early Paleocene to the Middle Eocene in Europe and were about the size of a sheep, with tails making slightly less than half of the length of their bodies and unlike their ancestors, good running skills for eluding predators. It was an animal approximately the size of a fox (2. It had 4. 4 low- crowned teeth, in the typical arrangement of an omnivorous, browsing mammal: three incisors, one canine, four premolars, and three molars on each side of the jaw. Its molars were uneven, dull, and bumpy, and used primarily for grinding foliage. The cusps of the molars were slightly connected in low crests. Eohippus browsed on soft foliage and fruit, probably scampering between thickets in the mode of a modern muntjac. It had a small brain, and possessed especially small frontal lobes. However, all of the major leg bones were unfused, leaving the legs flexible and rotatable. Its wrist and hock joints were low to the ground. The forelimbs had developed five toes, of which four were equipped with small proto- hooves; the large fifth . The hind limbs had small hooves on three out of the five toes, while the vestigial first and fifth toes did not touch the ground. Its feet were padded, much like a dog's, but with the small hooves in place of claws. During the Eocene, an Eohippus species (most likely Eohippus angustidens) branched out into various new types of Equidae. Thousands of complete, fossilized skeletons of these animals have been found in the Eocene layers of North American strata, mainly in the Wind River basin in Wyoming. Similar fossils have also been discovered in Europe, such as Propalaeotherium (which is not considered ancestral to the modern horse). It resembled Eohippus in size, but had a slimmer body, an elongated head, slimmer forelimbs, and longer hind legs, all of which are characteristics of a good jumper. Although Orohippus was still pad- footed, the vestigial outer toes of Eohippus were not present in the Orohippus; there were four toes on each fore leg, and three on each hind leg. The most dramatic change between Eohippus and Orohippus was in the teeth: the first of the premolar teeth were dwarfed, the last premolar shifted in shape and function into a molar, and the crests on the teeth became more pronounced. Both of these factors gave the teeth of Orohippus greater grinding ability, suggesting Orohippus ate tougher plant material. Epihippus. In the mid- Eocene, about 4. Epihippus, a genus which continued the evolutionary trend of increasingly efficient grinding teeth, evolved from Orohippus. Epihippus had five grinding, low- crowned cheek teeth with well- formed crests. A late species of Epihippus, sometimes referred to as Duchesnehippus intermedius, had teeth similar to Oligocene equids, although slightly less developed. Whether Duchesnehippus was a subgenus of Epihippus or a distinct genus is disputed. The forests were yielding to flatlands. In a few areas, these plains were covered in sand. In the late Eocene, they began developing tougher teeth and becoming slightly larger and leggier, allowing for faster running speeds in open areas, and thus for evading predators in nonwooded areas. About 4. 0 mya, Mesohippus (. It walked on three toes on each of its front and hind feet (the first and fifth toes remained, but were small and not used in walking). The third toe was stronger than the outer ones, and thus more weighted; the fourth front toe was diminished to a vestigial nub. Judging by its longer and slimmer limbs, Mesohippus was an agile animal. Mesohippus was slightly larger than Epihippus, about 6. Its back was less arched, and its face, snout, and neck were somewhat longer. It had significantly larger cerebral hemispheres, and had a small, shallow depression on its skull called a fossa, which in modern horses is quite detailed. The fossa serves as a useful marker for identifying an equine fossil's species. Mesohippus had six grinding . Mesohippus also had the sharp tooth crests of Epihippus, improving its ability to grind down tough vegetation. Miohippus. Around 3. Mesohippus, Miohippus (. As with Mesohippus, the appearance of Miohippus was relatively abrupt, though a few transitional fossils linking the two genera have been found. Mesohippus was once believed to have anagenetically evolved into Miohippus by a gradual series of progressions, but new evidence has shown its evolution was cladogenetic: a Miohippus population split off from the main Mesohippus genus, coexisted with Mesohippus for around four million years, and then over time came to replace Mesohippus. Its facial fossa was larger and deeper, and it also began to show a variable extra crest in its upper cheek teeth, a trait that became a characteristic feature of equine teeth. Miohippus ushered in a major new period of diversification in Equidae. It branched out into two major groups, one of which adjusted to the life in forests once again, while the other remained suited to life on the prairies. Kalobatippus probably gave rise to Anchitherium, which travelled to Asia via the Bering Straitland bridge, and from there to Europe. Its third toe was stronger and larger, and carried the main weight of the body. Its four premolars resembled the molar teeth and the first were small and almost nonexistent. The incisor teeth of Parahippus, like those of its predecessors, had a crown as humans do; however, the top incisors had a trace of a shallow crease marking the beginning of the core/cup. Merychippus. In the middle of the Miocene epoch, the grazer Merychippus flourished. It had wider molars than its predecessors, which are believed to have been used for crunching the hard grasses of the steppes. The hind legs, which were relatively short, had side toes equipped with small hooves, but they probably only touched the ground when running. The most different from Merychippus was Hipparion, mainly in the structure of tooth enamel: in comparison with other Equidae, the inside, or tongue side, had a completely isolated parapet. A complete and well- preserved skeleton of the North American Hipparion shows an animal the size of a small pony. They were very slim, rather like antelopes, and were adapted to life on dry prairies. On its slim legs, Hipparion had three toes equipped with small hooves, but the side toes did not touch the ground.
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