On June 14, the internationally renowned academic journal Nature published online the latest achievement "An Early Cretaceous Mammal and Placenta-Marsupial Dichotomy", which was jointly researched by Professor Zheng Xiaoting and Professor Wang Xiaoli from the School of Life Sciences (Institute of Geology and Paleontology) of Linyi University, Indiana University and vertebrate paleontology Institute of Paleoanthropology of China Academy of Sciences.

In the form of a research article, this paper reports a well-preserved early Cretaceous mammal fossil named hybrid animal. Mixed beast is an early type of real beast (placenta and its ancestors), which has the mixed characteristics of real beast and hind beast (marsupial and its ancestors).

It is found that marsupials and hybrids reported in China belong to the same family, and they are both early true mammals, not the ancestors of marsupials. This important discovery reveals the complexity of mammalian evolution, changes people's understanding of the evolutionary history of the differentiation of different groups of mammals, and makes people's understanding of the evolutionary history of mammals more and more clear.

Mixed animal specimens are kept in Shandong Tianyu Natural Museum. From the lower stratum of Yixian Formation in Ningcheng area of Inner Mongolia, the Jehol biota is 65.438 0.26 billion years ago. This is the most complete paleontological fossil discovered so far. The earliest hyoid structure and eardrum ring were found, which is of great significance to trace back its living habits, living environment and ecotype.

The researchers used high-precision CT scanning technology to reconstruct the fossil bones embedded in rocks in three dimensions, which basically restored the morphological characteristics of each bone. On this basis, the research team spent three years constructing a large-scale data matrix including 56 early mammal taxonomic units and more than 400 morphological features, and established a reliable early mammal pedigree tree.

Phylogenetic analysis showed that four species of mammals in Jehol biota belong to true mammals, including marsupials in China, which were previously classified as post-mammals. This research achievement is of great scientific significance. The new conclusion that marsupials in China belong to true mammals indicates that Asia may not be the origin center of marsupials. At present, the earliest known fossil record of marsupials is the triangle-toothed beast discovered in North America 1. 1 100 million years ago.