EOHIPPUS: CHARACTERISTICS, MORPHOLOGY, REPRODUCTION, NUTRITION - BIOLOGY - 2025

Eohippus is an extinct genus of animals, specifically mammals, that inhabited the planet during the Eocene epoch in the Cenozoic Era. They are considered the oldest ancestors of current horses.

Although physically they were not very similar to these, specialists have established, through the study of the various fossils, a connection between the Eohippus and the modern horse.

Graphic representation of the Eohippus. Source: Charles R. Knight

The fossil records have established that these animals inhabited several continents such as Asia, Europe and North America. They lived mainly in environments with many plants, jungle type, with abundant leaves, so their food was never lacking.

characteristics

The genus Eohippus was made up of complex animals, being considered multicellular organisms, which means that their cells were different and specialized in various functions.

These were triblastic animals, with the three germ layers, as well as coelomats and protostomes. They were animals in which the sex was separated, that is, there were male and female.

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

Taxonomy

The taxonomic classification of the Eohippus is as follows:

-Domain: Eukarya

-Animalia Kingdom

-Filo: Chordata

-Class: Mammalia

-Order: Perissodactyla

-Family: Equidae

-Gender: Eohippus.

Morphology

The member animals of the genus Eohippus were small, they could barely exceed 30 cm in height. In turn, they were quadrupeds and their limbs were short and had different numbers of fingers. The front ones had four fingers, while the rear ones only had three.

Its skull was small and not as elongated as that of modern horses. Her neck was short in length and her back was arched. This was probably because it was always grazing and cutting herbs with its snout.

They had complete teeth, with teeth adapted to grind food.

Reproduction

Taking into account that the organisms of the genus Eohippus belong to the group of mammals, it can be said that the type of reproduction they had was sexual.

Sexual reproduction involves the fusion or union of female (egg) and male (sperm) germ cells or gametes.

It is important to note that this type of reproduction is advantageous compared to asexual, since it is the main responsible for the existence of genetic variability.

This is what allows individuals of the same species to have different characteristics, which gives them the possibility of adapting to eventual changes in the environment, thus ensuring that the species survives through time.

Eohippus is considered one of the ancestors of the current horse, so, when talking about its reproduction, it can be said that it had a certain similarity with its reproduction.

Mating ritual

It is believed that, as with some current equidae, members of the genus Eohippus had some kind of mating ritual, something quite common among many mammals. For example, when the female reaches sexual maturity and is ready to reproduce, she sends a series of signals to the male to indicate this.

One of those signals may be the release of certain chemicals that are known as pheromones. These are generally released through urine. The effect of pheromones on individuals of the opposite sex is an irresistible attraction of a sexual nature.

Likewise, specialists believe that among males it is possible that they had a series of behaviors to attract the attention of the female, such as walking in front of them, fighting among themselves or emitting some type of characteristic sound.

Fertilization and embryonic development

Once the different mating rituals have been carried out, it is time for intercourse. In these animals, as in most mammals, fertilization was internal. This implied that the male had to introduce the sperm inside the female's body.

According to the collected fossils and the evolutionary history of equidae, it is stated that this animal had a copulatory organ through which it deposits sperm in the female. It is estimated that females of this genus most likely produced only one ovum at a time.

When the sperm met the egg, it penetrated it and a cell known as a zygote was formed. Later it began to undergo a series of mythotic divisions. Finally, the three germ layers are formed (endoderm, mesoderm and ectoderm), from which the tissues that would make up the adult animal are differentiated.

The duration of gestation is not defined, since it is not possible to obtain such information from fossils. However, experts believe that this could be similar to that of current horses.

Since these animals were mammals, a structure known as a placenta was formed during gestation. This was of vital importance, since it allowed communication between mother and child and, consequently, the passage of nutrients.

Birth

When embryonic development was complete and the new individual was ready to be born, the female went into labor. Finally, the foal, with characteristics similar to those of an adult animal, was born through the animal's vaginal canal. It is possible that the female took care of the foal for a time, until it could fend for itself.

Nutrition

Animals that belonged to the genus Eohippus were herbivores, that is, they fed on plants. Due to its small size, it most likely fed on small shrubs. The specialists affirm that the Eohippus was a browser (they feed on leaves and / or branches).

Although his teeth were quite specialized, with incisors, canines, molars and premolars, most of his teeth were short and tuberous in appearance. Because of this, they could only crush food, so they only ingested flexible and juicy plants. In addition, it could also feed on fruits and herbs.

Digestion

When the animal ingested the food, it was crushed in the oral cavity and mixed with saliva, in which chemical substances known as digestive enzymes are found. These enzymes contributed to the processing of food, since they began to break down the nutrients to make them easier to digest.

The food bolus then passed through the esophagus into the stomach where it was again mixed with digestive enzymes that continued to break down. Then it passed to the intestine, which was the place where the absorption of nutrients took place.

Because plants have certain components such as cellulose, which is difficult to digest by herbivorous animals, it was possible that in the intestines of these animals there were certain bacteria that helped in its degradation.

After the nutrients were absorbed, they were released to the outside in the form of feces.

References

1. Arita, H. (2010). The return of the horse: the macro and the micro in evolution. Sciences 97.
2. Evolution of the horse. Taken from: britannica.com
3. Hooker, JJ (1994). "The beginning of the equoid radiation." Zoological Journal of the Linnean Society 112 (1–2): 29-63
4. Horse evolution over 55 million years. Taken from:
5. MacFadden, B. (2008). Fossil horses from “Eohippus” (Hyracotherium) to Equus, 2: rates of dental evolution revisited. Biological Journal of the Linnean Society. 35 (1)