The study of the Fossil System of the Middle Jurassic Beast in the United Kingdom has achieved phased results

Comparison of the upper and lower dentitions on the left side of the three types of thieves, in which the teeth in the E-F dentition were once classified into four genera. (Courtesy of the research group)

Recently, the journal Systematic Paleontology published online collaborative academic papers by the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, the Natural History Museum in London, and the American Museum of Natural History in New York. This article reports on the fossils of exotic beasts (thief beasts, polynoodontics) produced in Woodeaton, a new site in the Middle Jurassic of the United Kingdom, and determines the long-standing morphological and taxonomic problems of thieves, discusses the homology of the tooth characteristics of heterogeneous beasts, and for the first time performs a first-level phylogenetic analysis of known thiefs.

Modern concepts of exotic beasts include polynoodonts, thief beasts, and gandwanatherians. Thief mammals are the earliest fossils of Mesozoic mammals reported in 1847, while the earliest polyodonts were reported in 1857. They are also two of the most controversial taxa in the study of Mesozoic mammals, a controversy that dates back at least to Owen’s 1871 monograph and continues to this day.

The reason for the controversy is that the shape of the beast is peculiar, and the second is that the fossils are preserved and broken. In particular, the fossils of thief beasts, before the report of the Yanliao biome of thieves, were basically single tooth specimens or broken jaws, and their understanding of them was very limited. Until 2010, there was a mistake in the left and right orientation of the teeth of the thief; The upper and lower teeth of the same genus and the teeth in different tooth positions are often identified as coming from different genera species or even different orders. Discussions of their evolutionary and phylogenetic relationships on such a basis are clearly problematic.

In the past 10 years, the well-preserved fossils of thieves in the Yanliao biota have provided new key fossil evidence for related research, and greatly enriched our understanding of the morphology and biological content of thieves. However, in early European related studies, the problem of fossil identification has not been properly revised. Although these specimens are incomplete, they are of great significance to the understanding of the evolution of exotic animals from the perspective of age, geographical distribution and morphological diversity.

The earliest thiefs were found in the Late Triassic strata of Europe, while the earliest, definitive polygnonates were found in the Middle Jurassic of Europe, Siberia and China. The understanding of them relates to the origin and early evolution of mammals and the relationships of high taxonomic metasystems.

The new specimen reported on the results comes from Woodeaton, England, which is slightly lower than the classic Oxfordshire and Dorset site Forest Marble Group (Bathonian period). Based on the new specimen, two new genera of thief species were established, one of which is Butlerodon, a famous British zoologist and paleontologist, who received the Romer-Simpson Lifetime Achievement Award from the North American Vertebrate Association in 1996, and was one of the pioneers in early mammalian tooth research.

The newly reported Thief shows transitional characteristics between the European Late Triassic and Middle Jurassic Forest Marble species and the Asian Middle and Late Jurassic species, which is important for understanding the continuous evolution of the Thief. The paper also reported a specimen of the upper teeth of polyodonts, one of the earliest known representatives of polyodonts. The fossil record at this site once again shows that both true thief and the earliest (Middle Jurassic) polyodonts existed in the fauna of Europe, Siberia, and East Asia, and existing fossils show that in these earliest combinations of exotic beasts, the fossil abundance and genus diversity of the thief were higher than those of polyodonts.

The article also systematically determines the British exotic specimens reported in the early years. Complex taxonomic issues were involved, including the replacement of occupied genera names, the consolidation of tooth specimens identified as four genera of thief and polyodontosaur, respectively, and the reinterpretation and reconstruction of the dentition morphology of the merged species. On this basis, the bite and tip homologous structure of the teeth of known thief are comprehensively discussed, and on the basis of tooth characteristics, the phylogenetic analysis of known species of thief is carried out for the first time.

The analysis results show that the jurassic heteroceros in Europe are closer to those in Asia; Like polyodonts and mammals, thief beasts were distributed globally during the Mesozoic Era. These new morphological contents and phylogenetic relationships, as well as related geological histories and paleogeographic distributions, provide new evidence for understanding the origin differentiation process of mammals.

The research has been funded by the National Natural Science Foundation of China, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, the Natural History Museum in London, and the American Museum of Natural History in New York. (Source: China Science Daily Cui Xueqin)

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