The beautiful bird is super "hot"! What kind of "strange bird" was discovered in the "Jehol Biota" that shocked China and the world?

1. Introduction to the Jehol Biota

The Jehol Biota lived in the middle of the Early Cretaceous, and its fossil sites are concentrated in western Liaoning, northern Hebei, and southeastern Inner Mongolia (Figure 1a). It has produced a large number of beautifully preserved fossils of various categories, representing the best-preserved terrestrial biota in the Cretaceous. Academician Zhou Zhonghe called it "the prototype of modern terrestrial ecosystems." The study of this biota is of great significance for our understanding of the origin and early evolution of some major biological groups in modern Earth ecosystems.

Figure 1 Geographical and stratigraphic distribution of the Jehol Biota sensu stricto (Xu Xing et al., 2019)

2. History of Jehol Biota Research

In 1923, American scholar AW Grabau proposed the term "Jehol Series" to refer to a set of lake-phase deposits containing wolf-finned fish fossils exposed near Lingyuan County, Rehe Province (now Lingyuan City, Liaoning Province), and believed that the deposits belonged to the Lower Cretaceous (Grabau, 1923); in 1928, he proposed the term "Jehol Fauna" to refer to "a set of animal fossil assemblages in the Jehol Series" (Grabau, 1928). In 1962, Chinese scholar Gu Zhiwei first proposed the terms "Jehol Group" and "Jehol Biota": the former is a lithostratigraphic unit extended from the "Jehol Series", covering not only lake-phase deposits containing fish fossils, but also volcanic rocks of the same period; the latter is used to refer to a set of animal and plant fossil assemblages in the Jehol Group (Gu Zhiwei, 1962).

Figure 2 The discovery process of the Jehol Biota

Early studies of the Jehol Biota also identified three representative molecules, namely, Oriental Leaf-limbed Ostraconidia-Pseudo-Ephemeroptera-Lycoptera (Figure 3). These three representative molecules and some other molecules are not only distributed in western Liaoning, northern Hebei and southeastern Inner Mongolia, but also found in wider areas, so there is the concept of "broad Jehol Biota", which refers to a terrestrial biota with a geographical distribution range including northern China, the Korean Peninsula, Japan, Mongolia, Kazakhstan and Siberia. Subsequently, starting from the 1990s, the study of the Jehol Biosphere entered a peak period, marked by the discovery of early bird fossils. In addition to bird fossils, it also includes feathered dinosaurs, insect fossils, and plant fossils (Figure 4). These discoveries provide key information for the origin and early evolution of some important biological groups, making the study of the Jehol Biota gradually become a hot research direction in paleontology.

Figure 3 Three representative molecules of the Jehol Biota identified in early studies (Huang and Ren, 2008)

Figure 4 Confuciusornis, (b) Jeholornis, (c) Protopteryx, (d) Yixianornis; feathered dinosaurs: (e) Sinornithosaurus, (f) Caudipteryx, (g) Microraptor; early mammals: (h) Zhanghetheon, (i) Archaeotherium; (j) early flea Tyrannosaurus; (k) early angiosperm Archaeocarpus. All photos are not scaled (Xu Xing, 2019)

Rehe beautiful bird is super hot

1. Confuciusbird

The discovery of some early bird fossils in the Jehol Biota has provided a lot of evidence for the study of the origin and early evolution of birds. The first is the discovery of Confuciusornis, which has a beak and pygostyle like modern birds, but retains the diapsid reptiles' bitemporal fenestra (Hou et al., 1995, 1999), and is an early branch of bird evolution. The ancestors of birds, dinosaurs, had teeth, while modern birds do not. The skull of Confuciusornis has no teeth on both the upper and lower jaws, but has a thick keratin beak - it is the earliest ancient bird in the world to have a keratin beak, representing the transition from teeth to beak. Confuciusornis represents the first fossil of completely degenerated teeth in the process of dinosaur evolution to birds.

Figure 5 Confuciusbird

2. Jehol Bird

Jeholornis is the most primitive bird found in my country so far, and its primitiveness is second only to the oldest bird, Archaeopteryx. Compared with the famous Confuciusornis, Jeholornis has obvious characteristics and is more primitive, representing an older ancestral type of early bird evolution. Jeholornis is the only primitive bird with a long bony tail discovered so far, except Archaeopteryx. Its notable feature is that it retains a very slender tail composed of more than 20 caudal vertebrae. Modern birds have a small number of caudal vertebrae, and the last few segments are fused into a bone rod called "pygostyle" for the attachment of tail feathers. However, among the known fossils, only Archaeopteryx has preserved complete caudal vertebrae and lacks a pygostyle. Jeholornis represents the second bird to preserve a complete long tail, and the pygostyle has not yet developed. The preserved long tail is obviously a feature of the ancestors of reptiles.

Figure 6 Jehol bird

In addition to bird fossils, the Jehol Biota also has many important discoveries related to insect, plant, and mammal fossils. These discoveries have greatly helped us understand the types of organisms, climate, and environment in the early Cretaceous period. They have also helped us solve many questions related to early biological evolution, the co-evolution of organisms and the environment, and other issues. Researchers will not stop their research on the Jehol Biota, and look forward to more great discoveries.

References

Xu Xing, Zhou Zhonghe, Wang Yuan, Wang Min. Review and Prospect of Jehol Biota Research. Science China: Earth Sciences, 2019, 49(10): 1491-1511

Grabau A W. 1923. Cretaceous Mollusca from north China. Bull Geol Surv China, 5: 183–198

Grabau A W. 1928. Stratigraphy of China. Part 2 Mesozoic. Beijing: Geological Survey of China. 774

Gu Zhiwei. 1962. Jurassic and Cretaceous of China. Beijing: Science Press

Huang, J.D., Ren, D. 2008. Trichodina may not exist in the Jehol Biota of China. Geological Review, 54: 602–609.

Hou LH, Zhou ZH, Gu Y, Zhang H. 1995. Confuciusornis sanctus, a new Late Jurassic sauriurine bird from China. Chin Sci Bull, 40: 1545–1551

Hou LH, Martin LD, Zhou ZH, Feduccia A. 1999. A diapsid skull in a new species of the primitive bird Confuciusornis. Nature, 399: 679– 682