The chart shows the changes in the diversity of Cenozoic odd-ungulates in Asia and the degree of molarization of the premolars of different branches of the odd-ungulates. (Photo courtesy of the research team of the Institute of Paleovertebrate Vertebrate of the Chinese Academy of Sciences)
BEIJING, June 16 (Xinhua) -- In the field of paleontological evolution, the traditional view is that the diversity of Cenozoic chickades in Asia, affected by global climate change, experienced its largest decay at the turn of the Eocene/Oligocene (about 33.9 million years ago), and the latest research results completed by Chinese and foreign scientists pushed the time forward by 6 million years, believing that its most significant decay occurred in the late Meseocene (about 39.9 million years ago).
Bai Bin, Zhang Zhaoqun, Wang Yuanqing, and Mengjin of the American Museum of Natural History, and Christine Janis of the University of Bristol in the United Kingdom found that due to the gradual decline in global temperatures after the "Moderate Climate Period of the Middle Eocene", at the end of the Miocene, the vertebrate tapir family became extinct, the Family of Tapirs decreased from 4 genera to 1 genus, and the decline in the genus of the rhinoceros superfamily was more than half. This phenomenon may also apply to other mammalian taxa.
Since this obvious diversity decay occurred in the Asian mammal staging known as the "Ulangochu period" in the late Miocene, Chinese and foreign co-researchers proposed that the largest decay of the Cenozoic odd-ungulate diversity in Asia should be called "Ulangochu decline", and the relevant research results have recently been published in ecology and evolution, an open access journal owned by Wiley, an internationally renowned publisher.
The scientific research team of the Institute of Paleovertebrates of the Chinese Academy of Sciences was interviewed on the 16th, and most of the odd-ungulate premolars have a gradual molarization process in the process of evolution, such as the living odd-ungulates (horses, tapirs, rhinoceros) have completely molarized premolars, in order to increase the area of chewing grinding, which is particularly important for odd-unmolars that are mainly based on oral chewing and grinding food, and the pseudolobes of the hindgut fermentation; and the anterior molars of the anterior intestine fermentation, such as regurgitations and camels, are only partially molarized. Moreover, the degree and pattern of molarization of different taxa of odd-ungulates are different, but their impact on the evolution and adaptation of odd-ungulates has not been studied accordingly.
The team, in collaboration with their U.S. and British counterparts, has shown through statistical and molarization levels of Asian Cenozoic fossils that most of the taxa formed by the separation of the anterior or posterior cusp from the global Cenozoic climate change is highly molarized, and that the taxa produced by molarization through sub-tips is more likely to extend into the Neogene, such as tapirs, rhinoceros, and macroceros, while the taxa with low molarization, and molarization separated by anterior or posterior cusp, is mostly extinct before the Neogene period, such as the Dai's tapir family became extinct at the end of the Mesocene. Amphibian rhinoceros and hoofed rhinoceros became extinct at the end of the Oligocene, and Terynes became extinct in the Late Eocene.
Chinese and foreign scientists believe that in the Eocene and Oligocene, the degree and pattern of molarization of premolars of odd-hoofed species are important influencing factors for the development or decline of related taxa. By the Recent Age, the premolars of the odd-ungulates had already had a high degree of molarization, and the evolution of the buccal teeth of horses and rhinos (including the premolars) turned into the elevation of the crown and the complexity of the enamel structure, reflecting the ability to resist the abrasion of high-fiber foods and the adaptation to open, arid environments. (End)