China News Service, Beijing, June 22 (Reporter Sun Zifa) The reporter learned from the Institute of Paleontology and Paleontology of the Chinese Academy of Sciences on the 22nd that the doctoral student Jiang Zuoqi and the American Museum of Natural History John Flynn Cooperation, through the latest research on fossils in the Middle Miocene of the United States (about 12-14 million years ago), found the earliest Xiong subfamily fossil to date and named it Tirawa Shu Xiong (abbreviated as Shu Xiong). Push 5 million years.
They also collaborated on a detailed study of the bear tooth grinding model, revealing how the bear subfamily's diet evolved through the adaptive development of the teeth, and eventually evolved from carnivorous animals to vegetative animals. This important paper on paleontological research by Chinese aesthetics has recently been published online in the international academic journal iScience.
The phylogenetic location of the Tilawarsh bear. (Photo courtesy of Jiang Zuoqi)
Jiang Zuoqigao interviewed reporters on the Internet on the 22nd and said that the Xiong Yake's fossil record was originally from the late Miocene, represented by the Dai's ancestor bear in Hezheng, Gansu, China, but Xiong Yake's sister group-giant panda The subfamily appeared as early as the late Miocene, indicating that Xiong subfamily should appear earlier. The latest research found that the Shushu fossils were taken from the Miocene Lover Formation in Nebraska in the central United States, which coincides with the earliest evidence of the giant panda subfamily fossils. It also confirms that the Xiong subfamily is at least in the middle. The new age has appeared.
Through a detailed phylogenetic tree, the researchers not only argued that the bear belongs to the earliest bear subfamily to date, but also indicated that many species that were classified as ancestral bears in the past actually belonged to different branches. The model of the ancestor bear, the short-nosed ancestor bear, may belong to the stem group of the Ursidae family. The primitive ancestor bear common in Europe belongs to the early giant panda subfamily, while the Lin Zuxiong in southern China is already a member of the ursus subfamily. The original ancestors, Lin Zuxiong, etc. should all establish new genera to distinguish them from model species, but this aspect involves a lot of materials, and more detailed classification and revision work will be needed later.
The evolution of the tooth structure of Xiong subfamily. (Photo courtesy of Jiang Zuoqi)
Jiang Zuoqigao pointed out that there are many studies on giant pandas in bears. Giant pandas are highly specialized in morphology and have a low metabolic rate, which can maintain a larger body size, but members of the Xiong subfamily are not so specialized, but they can still maintain it. The main food source is omnivorous, and the energy source is still largely plant food. To make up for the gaps in research related to this phenomenon, Chinese and American researchers have also studied bear tooth grinding patterns in detail, and found that the grinding method of the bear subfamily is unique among carnivores.
Xiong subfamily through a series of tooth tip structure reorganization, the connection between the internal and external directions of the teeth gradually disappear, so that the upper and lower jaws can move back and forth. This grinding method is morphologically convergent and evolutionary with polyomatous beasts, and functionally converges and evolves with the common "herb-dominant herbivorous, non-picking food types" common among herbivores. At the same time, the grinding mode in the front and back direction of the Xiong subfamily promoted the extension of the posterior molars of the Xiong subfamily members, further improving the grinding efficiency. The study found that the tooth structure of Dawn Bear exactly represents the initial state of this transition, which improves the grinding efficiency of the Ursus subfamily, so that they can eat plant food more effectively, and still use plants as the basis for maintaining a larger body shape. Staple food.
A further study on the diet and exercise patterns of the Shu Xiong found that the tooth tip was slow, the caries were common on the teeth, and the mandible was thick. It was obviously adapted to plant foods, and may eat higher sugar content such as fruits. The geometrical morphological studies of the bones of the dawn bears indicate that they may have strong tree-climbing behavior, while the existing bears are mainly ground-dwelling. This indicates that the strong tree-climbing abilities retained in some existing bears, such as Malay bears and spectacled bears, may be the remains of ancestors. "It also reveals that the process of biological evolution is often more complicated, and it may be inaccurate to rely on existing biological species for ancestral state reconstruction," Jiang Zuoqi said. (Finish)