It was learned from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences that Professor Bi Shundong of the Key Laboratory of Paleontology Research of Yunnan University, in cooperation with the Center for Excellence in Biological Evolution and Environmental Excellence of the Chinese Academy of Sciences and other units, found the most complete preservation of early Cretaceous mammal fossils in the fossils excavated from the Rehe biota, named "mixed metamorphic beast". The study found that the previously reported Chinese possum and the hybrid are of the same family, both early true mammals, not the ancestors of marsupials, which means that the conclusion that marsupials originated in Asia is debatable.
Zhou's Mixed Element Beast Restoration Diagram. Courtesy of the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences
The results were published online in the academic journal nature in the early morning of June 14, Beijing time.
With the help of new technologies such as high-precision CT scanning technology and digital three-dimensional reconstruction, the research team found mixed-element beasts in these "old" fossils and identified them as a new species. Bi Shundong introduced that the fossil bones of the mixed element beast are well preserved and exquisitely structured, and researchers have basically restored the morphological characteristics of each bone. For the first time, the mesozoic mammalian complete hyoid organ was preserved—the hyoid bone artifact, suspended between the skull and the laryngeal knot, was a series of slender bones that provided attachment to certain muscles of the tongue and neck, and was an important feeding, chewing, and vocal organ of mammals, and because they did not form joints with any other bone, they were difficult to preserve in fossils. The hyoid bone of the hybrid beast consists of 7 bones, while the human hyoid bone is made up of a single bone of a U shape. Reviewers in the journal Nature believe that this discovery will bring new insights to the study of many fields of biology and medicine.
A positive specimen of the Zhou's mixed-element beast. Profile picture
More importantly, the discovery could rewrite the conclusion about the origin of marsupials. Living placentals and marsupials account for 99% of mammalian species, humans belong to the placental class, and kangaroos are marsupials. The biggest feature of marsupials is that the female has a nursery bag in the abdomen, and the larvae are born very immature and must breastfeed long-term inside the mother bag. We now know that the "ancestors" of placental animals were true beasts, and the "ancestors" of marsupials were post-mammals, but where did they originate and when were they differentiated? This is considered a key scientific question in the study of mammalian evolution and has greatly influenced the pattern of modern Earth's ecosystems.
Chinese scientists have found a number of mammal specimens in the Rehe biota 126 million years ago, which have been identified as 3 genera and 3 species. Among them, Chinese possums are often considered to be the earliest fossil records of post-mammals, that is, the "ancestors" of living marsupials, so some scientists believe that marsupials originated in Asia. Bi Shundong said: "Due to the research conditions at that time, it was difficult for scientists to obtain detailed anatomical evidence, so this conclusion has been controversial. ”
Based on the full understanding of the hybrids, the research team spent 3 years to construct a large data matrix including 56 early mammal taxonomic units and more than 400 morphological features, and established a reliable early mammalian lineage tree. It was found that the mixed element mammals were the early types of euphrasiacs, but at the same time developed mixed characteristics of euphropods and post-mammals, and the phylogenetic analysis results showed that the four mammals in the Rehe biota, including Chinese possums, belonged to the euphropods. This means that the earliest known fossil record of marsupials is that of triangular toothed beasts found in North America 110 million years ago, and the previous conclusion that marsupials originated in Asia is debatable.
Bi Shundong introduced that the genus name of the mixed element beast means that the yuan qi is not divided, the chaos is one, and the beginning of the yuan qi is also the beginning, indicating that the creature has the special attribute of the mixed characteristics of the real beast and the post-beast. The species name Zhou is named after the surname of Zhou Zhonghe, an academician of the Chinese Academy of Sciences and a paleontologist.