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A Brief History in Time

Updated: Jul 10, 2018

Something that is fundamental to understand before discussing anything related to wild horse management is how these horses came to be in North America. There tends to be a lot of confusion when we talk about this subject and we find ourselves asking, “Are these horses native to the Americas?”


Short answer: No.


Why?


The horse that roams our rangelands and forests today is a very different horse than the one that evolved here millions of years ago. Roughly fifty-five million years back, in an era known as the Eocene Epoch, North America was a luscious, moist jungle with mammals in every corner. Imagine the Modoc today, a high desert, covered once with swamps and lush jungle forests. During this time, a four-toed, hunch-backed, browser roamed the area. This animal is called the Hyracotherium-shown above-and is believed to have begun the push towards what we know today as the horse (Equus ferus caballus).

The three toed Miphippus

When the climate during the Eocene began to change, grasses spread and soon dominated the landscapes. As these open spaces were exhausted with predators, prey retreated into the safer, denser, forests. Due to these environmental pressures, the Hyracotherium evolved and split into two lineages, the Miohippus-on the left- and Mesohippus. Both of these animals lost a toe, were taller and stronger, and had wide-set eyes for seeing predators. However, one major change in the Miohippus’s mouth caused this horse-like animal to be more successful. The Miohippus mouth consisted of longer and wider molars, allowing them to be more successful grazers on the rangeland, rather than foraging in the forests.


As the scenery changed, the Miohippus evolved into a descendent that we call the Parahippus-shown to the right. This new and improved addition to the lineage is important for two reasons: their teeth and their digestive system. The teeth that horses have allow them to graze continuously. They grow and are grinded down, much like a mechanical pencil. Horses also have a post-gastric gut. This allows them to consume a spectrum of food, making them generalists.


The adaptations that Parahippus evolved are what lead to the great success of the evolution of the horse, even the horses we see roaming the Devil’s Garden. During the Miocene, between twenty three and five million years ago, the lineage of the horse exploded, leaving North America with nineteen species.


This biodiversity boom did not last forever though. Approximately twelve thousand years ago, the equine-like species that roamed North America, among many other animals, began to disappear. It is still unsure as to how this great extinction happened, some scientist say a drastic shift in climate, while others say hunting, potentially both. Regardless, it would be a long time before the horse-shown above- set foot on American soils again.


This timeline leaves no room to question if the horses we see on the Devil’s Garden, or the ones wandering North America, are native. The species of horse we see today are not the same species of equine that evolved on this land millions of years back. Introduced, nonnative. As simple as that.


-M





The facts from this article were found here:


Ceballos, G., P. R. Ehrlich, and R. Dirzo. 2017. Population losses and the sixth mass extinction.

Proceedings of the National Academy of Sciences: 1-8


Orlando, L. et al. 2013. Recalibrating Equus evolution using the genome sequence of an early

Middle Pleistocene horse. Nature 499: 74-78


Shoemaker, L. and A. Clauset. 2013. Body mass evolution and diversification within horses

(family Equidae). Ecology Letter 17:211-220.


Solounias N., M. Danowitz, E. Stachtiaris, A. Khurana, M. Araim, M. Sayegh, and J. Natale.

2018. The evolution and anatomy of the horse manus with an emphasis on digit

reduction. The Royal Society 5: 1-21


Williams, C.A. 2004. Digestive system limitations. Rutgers Cooperative Research &

Extension 38:1-4.

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