Pliohippus

Pliohippus (Greek: pleion "more" and ippos "horse") is an extinct Equidae (horse family) genus. They were found approximately 15 million years ago, in the middle of the Miocene. It was a horse genus that lived in North America during the Pliocene Epoch (5.3–2.6 million years ago). This species was developed from Merychippus, a three-toed horse from the Miocene Epoch (23–5.3 million years ago). Pliohippus teeth are larger and more complexly folded than those of previous horses, indicating a higher reliance on grazing rather than foraging for food. They live on wide plains because of their diet and adaptations for running.

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Pliohippus Horse

The Pliohippus horse from Equidae (horse family) genus. They appeared approximately 15 million years ago, in between the Miocene and Pilocene. It has long and slender limbs, indicating that it is a quick-footed steppe animal. Some species have just one toe on each leg, whereas others have three (the main toe and two non-functional side toes). was believed to be the ancestor of the modern horse and its Equus cousins until recently, due to its many anatomical similarities. Despite the fact that Pliohippus was clearly an equid and therefore linked to Equus, its skull had deep facial fossae, which were not discovered in any Equus member.

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Pliohippus teeth were also highly curled, unlike modern horses teeth, which are very straight. As a result, it's unlikely to be the ancestor of the modern horse; instead, it's more likely to be Astrohippus' ancestor. It was around 1.25 metres tall, which is about the same height as a modern horse.

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This horse is like the modern horse, was a grazer that lived in the North American plains and ate steppe grasses. The fossils have been discovered in a variety of late Miocene locations in Colorado, the Great Plains (including Nebraska's Ashfall Fossil Beds and the Dakotas), and Canada. It was discovered with Neohipparion.

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Evolution of Pliohippus

Pliohippus marks the next stage in the evolution of horses, after Merychippus. This horse is a remarkable even more developed hoof foot supported by the middle toe, with the two side toes reduced to the point where they would have been hardly visible if at all in life. However, whether they are similar to modern horses belonging to the Equus genus is still debated. It was ancestral, but it is possible to rise to other species such as Astrohippus or Dinohippus, which are regarded to be more closely related to present forms due to their greater similarity. 

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Pliohippus is differentiated from modern forms by the presence of two pits in the skull in front of the eyes, a trait that is missing in modern forms. Space to accommodate larger face muscles to even resonating chambers that allowed modification of the sounds of its calls have all been proposed as explanations for these pits. Despite these suggestions, the function of these pits is still largely unknown.

Because species was formerly assumed to live during the Pliocene (the line between the Miocene and Pliocene has been re-established since Pliohippus was named), Pliohippus is often credited with meaning "Pliocene horse," but the "Plio" part translates as "more." Pliohippus, on the other hand, can still mean more like a horse than other (earlier) prehistoric horses in this situation.

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Pliohippus Facts

• Pliohippus lived in North America from the Late Miocene to the Pliocene.

• The size of a Pliohippus is comparable to that of a modern horse.

• Pliohippus can run as fast as a horse.

• Herbivorous Pliohippus

• Pliohippus teeth are larger and more complexly folded than those of previous horses.

Did You Know

How Did the Horse Evolve?

The horse, a mammal of the Equidae family, evolved over 50 million years, from a tiny, dog-sized, forest-dwelling Eohippus to the contemporary horse. Paleozoologists have pieced together a more complete outline of the modern horse's evolutionary ancestry than any other animal. Much of this development occurred in North America, where horses first appeared 10,000 years ago and then went extinct. The horse is a member of the Perissodactyla order, which includes animals with hoofed feet and an odd number of toes on each foot, as well as movable upper lips and tooth structures.

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This indicates that horses, tapirs, and rhinoceroses have a common origin. Perissodactyls first appeared in the late Paleocene, fewer than 10 million years after the Cretaceous–Paleogene extinction. Horses appear to have evolved for living in tropical forests, but unlike tapirs and, to a lesser degree, rhinoceroses, contemporary horses have adapted to life on drier ground, in the considerably harsher climatic conditions of the steppes. Other Equus species have adapted to a wide range of intermediate environments. The contemporary horse's forefathers walked on multiple spread-out toes as a compromise for a life spent travelling over ancient woods' soft, wet ground. The equids' diets switched from leaves to grasses as grass species appeared and flourished, resulting in bigger and more lasting teeth. At the same time, when the steppes began to develop, the horse's forefathers needed to be able to evade predators at higher speeds. 

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Eocene and Oligocene: Early Equids

1. Eohippus

Around 52 million years ago, Eohippus appeared in the Ypresian (early Eocene) (million years ago). It was around the size of a fox (250–450 mm in height), with a springy, arched back and a rather short head and neck. It had 44 low-crowned teeth, with three incisors, one canine, four premolars, and three molars on each side of the jaw, in the normal pattern of an omnivorous, browsing animal. Its molars were uneven, dull, and rough, and they were mainly used for grind foliage. In low crests, the molar cusps were slightly connected. Eohippus ate soft foliage and fruit, perhaps like a modern muntjac, scampering between thickets.

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Eohippus lived for nearly 20 million years with few important evolutionary changes. As this early Equidae shifted from a mixed diet of fruits and foliage to one focused increasingly on browsing foods, the most significant change was in the teeth, which began to adapt to the changing diet.

2. Orohippus

Eohippus evolved into Orohippus over a 50-million-year period in the early-to-middle Eocene through a series of gradual changes. Although its name means "mountain horse," Orohippus was neither a horse nor a mountain resident. It was about the same size as Eohippus, but it had a thinner body, an elongated head, slimmer forelimbs, and longer hind legs, all of which are traits of a good jumper. The vestigial outer toes of Eohippus were not present in Orohippus, although it was still pad-footed there were four toes on each foreleg and three on each hind leg.

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3. Epihippus

Epihippus evolved from Orohippus in the mid-Eocene, about 47 million years ago, and continued the evolutionary trend of increasingly efficient grinding teeth. Epihippus had five cheek teeth with well-formed crests that grinded. Epihippus tardus, also known as Duchesnehippus intermedius, had teeth that were similar to Oligocene equids but were slightly less developed.

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4. Mesohippus

The climate of North America grew drier during the late Eocene and early Oligocene epochs (32–24 mya), and the earliest grasses emerged. The forests were giving way to flatlands, which were home to grasses and a variety of shrubs. These plains were covered with sand in a few places, creating an environment similar to today's prairies.  In the late Eocene, they began developing tougher teeth and grew slightly larger and leggier, allowing for faster running speeds in open areas, and thus for evading predators in non wooded areas.

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5. Miohippus

Miohippus ("lesser horse") appeared some 36 million years ago, shortly after Mesohippus. The earliest species was Miohippus assiniboiensis. Miohippus, like Mesohippus, suddenly appeared, albeit a few transitional fossils linking the two species have been found.

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Miocene and Pliocene: True Equines

1. Kalobatippus

Kalobatippus (or Miohippus intermedius, depending on whether it was a new genus or species) was the forest-adapted version, with lengthy second and fourth front toes that were well-suited to walk on soft forest floors. Anchitherium was most likely descended from Kalobatippus, who travelled to Asia via the Bering Strait land bridge and then to Europe.

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2. Parahippus

The Miohippus population that survived on the steppes is thought to be related to Parahippus, a North American animal around the size of a small pony with a large skull and a face feature similar to that of modern horses. Its third toe was larger and stronger, and it carried the majority of the body's weight.

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3. Merychippus

Merychippus, a grazer, existed in the Miocene epoch's middle. It featured wider molars than its forerunners, which were thought to have been utilised for crunching steppe grasses. The short hind legs possessed side toes with little hooves, but they most likely only touched the ground when running. Merychippus spread to at least 19 other grassland species.

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4. Hipparion

Hipparion, Protohippus, and Pliohippus are three Equidae lineages thought to be descended from Merychippus' several kinds. Hipparion was the most distinct from Merychippus, owing to its unique tooth enamel structure. Unlike other Equidae, Hipparion's inner, or tongue side, had a completely separate parapet. The North American Hipparion's skeleton is intact and beautifully preserved, showing an animal the size of a small pony.

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5. Pliohippus

Pliohippus evolved from Callippus around 12 million years ago. It looked much like Equus, except it possessed two long additional toes on both sides of the hoof, which were barely visible as callused stubs from the outside. It has long and slender limbs, indicating that it is a quick-footed steppe animal. Because of its many anatomical similarities, it is thought to be the ancestor of modern horses. Despite being a near relative of Equus, the skull possessed deep facial fossae, whereas Equus' skull had none at all.

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Modern Horses

Equus

The genus Equus, which includes all living horses, is thought to have descended from Dinohippus via the intermediate stage Plesippus. Equus simplices, a zebra-like creature with a donkey-like head, is one of the oldest animals. The oldest fossil discovered so far is from Idaho, USA, and dates back 3.5 million years. Equus livenzovensis has been found in western Europe and Russia, indicating that the genus migrated fast into the Old World.

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Conclusion

Pliohippus was a horse genus that lived in North America during the Pliocene Epoch (5.3–2.6 million years ago) Its teeth are larger and more complexly folded than those of previous horses, indicating a higher reliance on grazing rather than foraging for food. The Pliohippus horse was thought to have lived during the Pliocene. The species was formerly assumed to live during the Miocene, but this has been re-established since the line between the two time periods was re-established.