The Horse-Year Column — The Mysterious Horse with the Long Nose

Before we know it, the Year of the Snake is quietly approaching its end, and a new year is gradually drawing near. At this turning point between years, people often look back on the stories of the past twelve months while also anticipating the possibilities of the year ahead.

At just such a moment, Rodrigo happened to come across a particularly intriguing animal silhouette. Its outline is unusual, and it carries a subtle connection to the zodiac animal of the coming year. The hint is this: it is not the animal most people would think of immediately, yet its relationship with the “horse year” is unexpectedly fitting.

Can you identify the creature hidden within this silhouette?

Before revealing the answer, take a moment to guess. The figure may lead you into an evolutionary story that stretches back millions of years.

Figure 1. Silhouette of a mysterious animal。圖片來源： Zimices (Julián Bayona)，採用 CC BY 3.0 授權

The animal in the silhouette is Proboscidipparion pater, commonly called the long-nosed three-toed horse. This extinct member of the horse family lived during the Pliocene about five million years ago and is known from fossil discoveries in northwestern China, particularly in the regions of Gansu and Shanxi.

In size, it was not especially large. Estimates suggest a shoulder height of roughly 130–145 centimeters and a body mass between 300 and 420 kilograms, making it comparable to a modern medium-sized horse. At first glance its overall body plan would have looked very much like that of modern horses. A closer look, however, reveals two striking differences. First, it possessed a long, flexible snout somewhat reminiscent of that of a tapir. Second, its feet retained three functional toes rather than the single hoof characteristic of modern horses.

Figure 2. AI reconstruction of the ancestral long-nosed three-toed horse (Proboscidipparion pater), manually verified to conform to the morphology shown in current mainstream reconstructions

Despite the name “horse,” Proboscidipparion did not belong directly to the lineage that leads to modern horses. Instead, it was part of an earlier branch of the horse family known as the tribe Hipparionini. Members of this group were once widely distributed across North America, Eurasia, and even parts of Africa. Fossil evidence shows that hipparion horses had already evolved relatively high-crowned teeth with complex enamel folding. Such dental adaptations allowed them to handle a wide variety of foods. They could graze on silica-rich grasses while also browsing on leaves and tender branches. This combination suggests that many hipparion horses practiced a mixed feeding strategy rather than specializing exclusively on grass.

Figure 3. Skull fossil of the long-nosed three-toed horse。圖片來源：Bernor R.L, Wang S., Liu Y., Chen Y. & Sun B.，採用 CC BY-SA 3.0  授權。

The three-toed structure of their feet also differed markedly from the single-hoofed condition seen in modern horses. The central toe carried most of the body weight, but the two side toes remained functional. This arrangement provided additional stability on softer or uneven ground. As a result, these animals could move effectively along forest edges and in semi-open environments where the terrain might shift between woodland and open patches.

Within this already diverse group of hipparion horses, Proboscidipparion stood out as one of the most unusual species. In addition to the typical three-toed limbs shared by other members of its tribe, it developed an enlarged nasal region that formed a long snout. Such a structure is extremely rare within the horse family.

Why would an early horse evolve such a strange anatomical feature? The most widely accepted explanation points to ecological adaptation. Fossil skulls of Proboscidipparion reveal that the nasal bones were strongly retracted, extending backward above the first upper molar. This arrangement closely resembles the skull structure of modern tapirs and some other mammals with elongated snouts. The similarity suggests that Proboscidipparion likely used its flexible nose to help grasp and select soft vegetation, such as tender leaves. This feeding adaptation would have allowed it to exploit food sources that other horses might not have used as efficiently. By occupying a slightly different ecological niche, it could reduce competition with other members of the horse family.

Figure 4. Image of modern tapir species; the external appearance of the long-nosed three-toed horse may have resembled these animals。圖片來源：蕭漫，採用 CC BY-SA 4.0授權。

Thanks to this flexible lifestyle, Proboscidipparion persisted from the Pliocene into the early Pleistocene and became one of the longest-lasting representatives of the three-toed horses. Yet the very traits that once helped it survive eventually became disadvantages.

Beginning in the Pleistocene, global climates gradually shifted toward cooler and drier conditions. Moist forests that once dominated large areas began to shrink, replaced by expanding grasslands. This environmental transformation forced Proboscidipparion to compete more directly with other grazing horses already adapted to open plains.

At the same time, a new competitor arrived from afar. Horses of the genus Equus, which had evolved in North America, crossed the Bering land bridge into Eurasia. These newcomers possessed several advantages. Their teeth were higher crowned and more resistant to wear, enabling them to feed effectively on tough grasses. Their limbs had also evolved into a fully single-hoofed structure, allowing them to run more efficiently across hard, open ground.

Compared with these highly specialized grassland runners, Proboscidipparion faced increasing difficulty. Its flexible snout was less suited to feeding exclusively on coarse grasses, and its three-toed feet were not optimized for sustained running on firm plains. Over time, these disadvantages contributed to the decline and eventual disappearance of the three-toed horses.

Figure 5. Fossil distribution map of three-toed horses from 5 million to 3 million years ago; light purple indicates the long-nosed three-toed horse。圖片來源：Bernor R.L, Wang S., Liu Y., Chen Y. & Sun B.，採用 CC BY-SA 3.0 授權。

Looking back on this evolutionary story, it becomes clear that Proboscidipparion was not a “failed” species. On the contrary, it was highly successful within the ecological conditions of its own era. The challenge arose when the rules of the environment changed. Traits that once offered advantages could suddenly become limitations.

The story of the long-nosed three-toed horse reminds us that evolution is never a straight path. Instead, it is a continuing dialogue between organisms and the environments they inhabit. As the new year approaches, perhaps we can take inspiration from these ancient horses. Just as they adapted to shifting landscapes, we too may find our own rhythm amid change. When circumstances shift, there is no need to fear turning in a new direction—because the future is shaped not by where we begin, but by how we adjust our course.

Author: Rodrigo

References:

1. Bernor, R. L., Sun, B., & Chen, S. (2018). Shanxihippus dermatorhinus comb. nov. with comparisons to Old World hipparions with specialized nasal apparati. Journal of Vertebrate Paleontology, 38(3), e1442911. https://doi.org/10.1080/02724634.2018.1442911

2. Bernor, R. L., Kaya, F., Kaakinen, A., Saarinen, J., & Fortelius, M. (2021). Old World hipparion evolution, biogeography, climatology and ecology. Earth-Science Reviews, 221, 103784. https://doi.org/10.1016/j.earscirev.2021.103784

3. Wang, Xiaoming (2013). Fossil Mammals of Asia: Neogene Biostratigraphy and Chronology. Columbia University Press. ISBN 978-0-231-52082-9.