Sun Boyang exhibits and introduces the fossil specimen of the ancient three-toed horse of the Weihe River. Photo by Sun Zifa, a reporter from China News Service
BEIJING, March 10 (Xinhua) -- As a class of extinct horses that were once widely distributed on the earth in the Late Miocene (about 11.6 million to 5.33 million years ago), the migration and evolution of three-toed horses have been controversial. Among them, the "three-toed horse incident", that is, the related issues of the three-toed horse appearing in Eurasia for the first time, including when and how the three-toed horse was first moved from North America to eurasia, has long attracted the attention of the paleontological community.
The Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences (Institute of Paleovertebrates of the Chinese Academy of Sciences), Linxia Prefecture and Zhengzhou Museum of Paleozoological Fossils in Gansu Province recently cooperated to conduct a comprehensive comparative study of the new materials of three-toed horse fossils produced in the Linxia Basin of Gansu Province and the previous classic materials, and found that the Weihe three-toed horse and the Jia's three-toed horse should be merged into the same genus of the Weihe ancient three-toed horse; the three-toed horse originating in North America moved into Eurasia twice, and the Weihe ancient three-toed horse that arrived in China 11.5 million years ago was the earliest three-toed horse in Eurasia.
This important achievement paper that solves the mystery of the "three-toed horse incident" and reveals the ecological background of the Late Miocene has recently been published online by the international academic journal "Scientific Report".
The Three-Toed Horse Event is one of the most important biogeographic events
Deng Tao, the corresponding author of the paper and a researcher at the Institute of Paleovertebrates of the Chinese Academy of Sciences, introduced that the first migration of three-toed horses from North America to Eurasia in the Late Miocene was one of the most important biogeographic events at that time and one of the signs of the beginning of the Late Miocene.
The exact definition of the three-toed horse event, there are currently three definitions of the three-toed horse event, the ancient three-toed horse event and the ancestral three-toed horse event, which is a complex issue involving the classification of the three-toed horse and the exact category of the three-toed horse that originally arrived in Eurasia. For Eurasia, the detailed study of the earliest three-toed horse of the era is the key to solving the problem.
The fossil specimen material of the Weihe ancient three-toed horse studied this time. Photo by Sun Zifa, a reporter from China News Service
Deng Tao pointed out that the previous mainstream view was that the earliest three-toed horse in Eurasia was a three-toed horse living in Central Europe, and in recent years, some scholars believe that the three-toed horse in the Vienna Basin is earlier. In Asia, the earliest common three-toed horses of the Late Miocene were the Weihe Three-toed Horse and Jia's Three-toed Horse, which were discovered and named in Lantian, Shaanxi in 1978. These two three-toed horse species, which were widely distributed in northern China in the early Late Miocene, are believed to be closely related to the ancient three-toed horse in Europe, and are geographically closer to North America, the birthplace of the three-toed horse, and are expected to become an important part of the study of the three-toed horse event.
11.5 million years ago, the Weihe ancient three-toed horse was the earliest in Eurasia
Sun Boyang, the first author of the paper and an associate researcher at the Institute of Paleovertebrates of the Chinese Academy of Sciences, said that the two three-toed horse breeds of Weihe and Jia were previously classified into the ancient three-toed horse subgenus in Europe, and through the gradual and clear understanding of the taxonomic unit in recent years, it is shown that this unit can be promoted to a genus.
On the other hand, Weihe and Jia species coexist at most fossil sites, and through a comprehensive comparison of new and old materials, it is confirmed that the characteristics of the two species that were previously considered to be obvious differences are caused by intraspecific variation and preservation, and the two should be merged into one genus, namely the Weihe ancient three-toed horse.
Shaanxi Lantian and Gansu Linxia Basin Weihe ancient three-toed horse skull material. Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences
According to paleomagnetic studies in the Linxia Basin, the first time the distribution of the Weihe River ancient three-toed horse distribution recorded strata is about 11.5 million years old. The three-toed horse in the Vienna Basin should be classified as the ancient three-toed horse of Europe, estimated to be 11.4 million to 11 million years old. Therefore, the Weihe ancient three-toed horse is the earliest three-toed horse in China and the earliest in Eurasia.
He said that the three-toed horse and the living horse are two different evolutionary branches of the common ancestor, the three-toed horse was completely extinct 500,000 years ago, and the living horse continues to this day.
Three-toed horses moved from North America to Eurasia in two separate times
Sun Boyang pointed out that the functional and morphological characteristics of the limb bones of Mayaidae have strong indicative significance for the ecological environment. The analysis of limb bones in the new material of the Weihe ancient three-toed horse shows that the Weihe ancient three-toed horse has the ability to stand and run for a long time, which is conducive to its survival in the open environment, while the taxa living in Europe and North Africa in the same period are relatively weak in running ability and are more suitable for survival in closed jungle environments.
Thus, the latest findings on the early Miocene three-toed horse paint a complete ecological and zoogeographic picture – the three-toed horse that originated in North America migrated into Eurasia in two stages: the first was the ancient three-toed horse arrived in East Asia 11.5 million years ago, as a grassland type, and then migrated to Europe, where a woodland type appeared; the second was the ancestral three-toed horse arrived in West Asia 10.8 million years ago, a grassland type, and then migrated to North Africa, where a woodland type appeared.
Three-toed horse history and geographical distribution in Eurasia in the early Miocene. Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences
Deng Tao said that a large number of paleoenvironmental research data also consistently show that Asia in the early Late Miocene was dominated by arid and open environments, and the climate in Europe and North Africa was relatively humid, dominated by forest environments. In addition, multiple studies have shown that this drought situation in Asia is most directly related to the strong uplift of the Tibetan Plateau in the Miocene and the retreat of the Paratesis Ocean.
He believes that the three-toed horse originated in the Miocene (about 16 million years to 11.6 million years ago) originated in North America dominated by arid environments, and was highly adapted to the local environment when it arrived in Asia in the late Miocene, and soon radiated and expanded; when they entered Europe and North Africa, they could quickly produce types that adapted to the closed environment, reflecting the high degree of adaptation and self-adjustment ability of the three-toed horse to the environment, which was an important reason for its subsequent prosperity in Eurasia. (End)
The animal geography and ecological environment of the three-toed horse in Eurasia in the early Miocene. Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences