Mao Fangyuan (left) and Zhang Chi display the fossil specimens of chinese diggers and Chen's sharp toothed beasts found in the latest research, respectively. Photo by Sun Zifa
Beijing, April 8 (Reporter Sun Zifa) Reporters learned from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences on the 8th that mao Fangyuan and Zhang Chi, associate researchers of the institute, and Meng Jin, researchers of the American Museum of Natural History, have recently discovered two new species of mammals in the early Cretaceous (about 130 million to 110 million years ago) in the Rehe biota in northeast China, the Chinese digger and the Chen's digging ceral tooth, which are the first to be found in the Rehe biota.
Fossil specimens of Chinese diggers (left) and Chen's cerebellum found in the latest research. Photo by Sun Zifa
The fossil discovery of these two new genera and their research results were published online in the internationally renowned academic journal Nature late at night on the 7th, Beijing time. The study showed that mammals adapted to the habit of digging holes can be distinguished by unique characteristics of excavation behavior, although the Chinese digger and the Chen's sharp toothed beast are far related, but the two species have some similar characteristics, including they are short hindlimbs, shorter tails, thick claws, and more vertebral bodies (except for the tail vertebrae).
A fossil specimen of the Chen's exodus found in the latest research. Photo by Sun Zifa
The researchers believe that the adaptation of cave dwelling and excavation has evolved independently many times in different mammals, and the similar characteristics of Chinese diggers and Chen's cerapods have evolved independently under similar selection pressure, and they all show the convergent evolution characteristics of burrowing, with obvious limb and bone specialization that adapts to the life of digging earth cavers, and is also accompanied by deformation and quantitative changes of the vertebrae.
Mao Fangyuan presents the ecological restoration of the fossils of Chinese diggers and Chen's sharp toothed beasts found in the latest research. Photo by Sun Zifa
Mao Fangyuan, the first author and co-corresponding author of the paper, said that the Chinese digging beast is a three-column toothed beast (a mammal-like reptile) from the Jiufotang Formation in Liaoning Province, with a body length of 316 mm, and it is also the first three-column toothed beast found in the Rehe biota. Found in the Yixian Formation of Liaoning Province, the Chen's expendator is smaller than the Chinese exambler, with a body length of 183 mm, and is the more common true trilodont (a distant relative of modern placental mammals and marsupials) in the Rehe biota.
A fossil specimen of a Chinese excavator discovered in the latest research. Photo by Sun Zifa
The orthotype specimens of the fossils of both new genera species are largely well-preserved skeletons. Among them, the orthotype specimen of the Chinese digger beast preserves the most complete post-head skeleton of the three rows of known odonts, and is also the first fossil of a basal mammal found in the Rehe biota, representing the latest known remains of non-mammalian inferior foramorum.
Restoration map of the main mammals of the Rehe biota. Zhao Chuang draws
Compared with the species of ground walking and running, tree climbing, and swimming in the water, their limb bones become short and thick, especially the forelimbs, and the hind limbs are weaker; the humerus is strong, and its distal end is extremely wide, reaching 60-70% of the length of the humerus; the strong internal and external condyles are the attachment points of the wrist and the flexor muscles (medial) and extensor muscles (lateral), which can produce strong internal and external forces for excavation; the ulnar eagle's beak protrusion is long, and the proportion of the length of the rest of the ulnar bone distal to the pivot of the elbow joint is usually higher, reflecting the increase in external force in this animal.
Lactational phylogenetic framework and time of differentiation of major taxa. Chi Zhang Analyzes cartography
As a digging tool, the forelimbs of both animals have broad palms and long, strong claws, and the first phalange is significantly longer than the other phalanges, while the other phalanges and metacarpal bones are shortened and thickened. The long and flexible trunk, the short and thick neck, and the small tail reduce resistance are common adaptations to the limb bones of excavated cavemen. In particular, in the hind palm of the Chinese digging beast, the first metacarpal and phalangeal bone are completely degenerated and lost. The skull of the Chen's cerapid also reflects some related adaptation changes, the contour of the head is triangular, the snout is pointed, the nasal bone is thickened, the orbit is smaller, and the occipital enlargement is used to attach the neck and shoulder muscles to assist in digging the ground.
Schematic diagram of the main ecological habits of mesozoic mammals representing the comparison of phyla spine and the evolutionary development mechanism. Photo courtesy of Mao Fang Yuan
Comparison of teeth and limb bones of Chinese and Chen's sharp toothed beasts. Photo courtesy of Mao Fang Yuan
Mao Fangyuan said that the newly completed collaborative research based on the minimalist method and the likelihood method of phylogenetic analysis, from mammals as the main body, expanded to mammals, has become the most comprehensive analysis of mammalian phylogeny. Calculated by bayesian methods, the study also obtained the differentiation time of the main groups of mammals, which provides a time frame for understanding the evolution of mammals and a phylogenetic framework for explaining the evolution of mining cave dwellings and vertebral changes in different branches of mammals. (End)
Orthotype specimens of Chinese diggers and Chen's sharp toothed beasts. Photo courtesy of Mao Fang Yuan
Ecological restoration map of Chinese digging beasts and Chen's digging cerapids. Zhao Chuang draws
Source: China News Network