MESOHIPPUS: CHARACTERISTICS, SPECIES, REPRODUCTION, NUTRITION - BIOLOGY - 2025

Mesohippus is a genus of animals belonging to the Equidae family that is currently extinct. Specialists agree that these horses were the link between primitive horses and current horses.

The date of most of the fossils is about 35-40 million years, so it is stated that these horses existed during the Oligocene epoch, in the Paleogene period of the Cenozoic.

Graphic representation of horses of the genus Mesohippus. Source: Remove «cropped» from file name and see original file

Its fossils were discovered and described for the first time by the American paleontologist Othniel Marsh in 1875. Most of the fossils have been found in the North American continent, especially in lands of the states of Nebraska, Dakota and Colorado, as well as in some regions from Canada.

Taxonomy

The Mesohippus taxonomic classification is as follows:

-Domain: Eukarya

-Animalia Kingdom

-Filo: Chordata

-Class: Mammalia

-Order: Perissodactyla

-Family: Equidae

-Gender: Mesohippus

characteristics

Taking into account that these ancient horses belonged to the Animalia kingdom, specifically the Mammalia phylum, it can then be said that they had the characteristics of said phylum, such as that they were multicellular eukaryotic organisms.

Likewise, their embryonic development must have been similar, so they were then triblastic animals, with the three germ layers: ectoderm, endoderm and mesoderm. From these originated the different cells that made up the individual, and therefore, the tissues and organs specialized in specific functions.

They were animals with bilateral symmetry, that is, made up of two exactly equal halves, taking the longitudinal axis of the body as a point of reference.

Likewise, these animals were autotrophs, unable to synthesize their own nutrients. Their diet was purely herbivorous, based on shrubs and other small plants.

They reproduced in a sexual way, with internal fertilization and direct development. They were viviparous.

Morphology

As mentioned above, the horse of the genus Mesohippus forms the link between primitive horses and modern horses. Because of this, their anatomical features had a bit of both groups.

First of all, in terms of size, their legs were slightly longer than those of their predecessors, so they could reach a height of approximately 60 cm. All this, according to the data collected from the collected fossils.

The head of the Mesohippus elongated forward, outlining the snout of today's horses. It was also slightly larger than that of its ancestors, which implies that its cranial cavity was also wider. This allows us to intuit that his brain was bigger too.

Likewise, the fossil records have made it possible to establish what the teeth of these horses were like. It has been determined that their teeth were very similar to those of current horses, being these larger than those of the ancestors, with higher crowns, which allowed them to access a much more complete diet.

Comparison between fossils of various genera of horses. Source: H. Zell (User: Llez)

Species

This extinct genus of mammals was made up of a total of 13 species. These are named below:

Reproduction

Because Mesohippus is a genus of organisms that are extinct, the information we have about them comes from the fossils that have been collected. Taking this into account, when talking about its most important physiological aspects, one enters the realm of speculation.

Since the horses of the genus Mesohippus are seen as the transitional link between the primitive species of horses and the modern horse, it is possible to affirm that their reproduction was similar to that of current horses.

In this sense, these horses were mammals and as such, their type of reproduction was sexual, with internal fertilization and viviparous.

Possible mating rituals

It is not known whether mating rituals existed among them, as there are among modern horses. If there had been, the prolonged, energetic whinny was probably part of that ritual, as well as the frontal approach to the mare.

Likewise, it is to be expected that the mares of this genus emit signals when they are in heat, that is, ready to mate. These signs include an open behavior towards the male, making him see that he is ready to mate.

Likewise, mares tend to urinate with a mucous-like discharge, in which it is believed there may be pheromone-like chemicals.

Fertilization, pregnancy and birth

In these animals, as mammals that they are, it is to be assumed that fertilization is internal. Like their current descendants, they had to have a copulatory organ, through which they could introduce sperm into the female's body, specifically into the genital tract.

Once this happened and the ovum was fertilized, then the pregnancy began, the duration of which is not specified. After the appropriate time elapsed in which the embryo developed in its entirety and the foal was formed, delivery occurred.

It is important to note that, like all mammals, they developed a placenta, a structure through which nutrients pass from the mother to the developing fetus.

Product of childbirth, a foal was born that had characteristics similar to those of an adult horse, which is why it can be said that the species of the genus Mesohippus presented a direct development, since they do not go through larval stages or anything related to this.

Nutrition

These horses were herbivores, which means that they fed on bushes and herbs. The shape and size of his teeth facilitated this type of feeding. It is noteworthy that the teeth of horses of the genus Mesohippus were longer than those of their predecessors, more closely resembling those of modern horses.

Likewise, the teeth of the Mesohippus present a novel character, consisting of high crowns. This allowed it to feed on shoots, leaves and herbs, which formed the basis of its diet.

Once the food was entered into the oral cavity, it was subjected to the action of the various digestive enzymes that were immersed in the saliva of the animal. In addition to this, the shape and size of their teeth facilitated the grinding of the food that, together with the saliva, turned the food into an easy-to-swallow bolus.

The food bolus passed through the esophagus to the stomach, where it was again subjected to the action of digestive juices. Later it passed to the small and large intestine, which is where the absorption of nutrients was carried out. Subsequently the waste was released through the anus.

As with all herbivorous animals, in the digestive tract of horses of this genus there must have been bacteria and microorganisms that contributed to the digestion of the components of the food that the animal ingested. Those bacteria helped break down food even more, to make it easier to digest. This is the same as in modern horses.

References

1. Arita, H. (2010). The return of the horse: the macro and the micro in evolution. Sciences 97.
2. MacFaden, B. (2005). Fossil horses - evidence for evolution. 307.
3. Mora, M., Blanco, A. and Gil, M. (2005). Equus and its fossil record in the Pleistocene of North America. VII Symposium of Zoology.
4. Retrieved from:
5. Palmer, D. (1999). The Marshall illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions.
6. Valentine, R. (1975). The Evolution of the Horse. Journal of reproduction and fertility. Supplement. 2. 3.