Origin[ edit ] Some scientists have argued that the Jehol Biota evolved directly from the preceding Daohugou Biota without any strongly defined division. However, the absolute dating of the Daohugou beds has been the subject of divergent opinion: in , Wang et al. Several other research teams, including Liu et al. Liu et al. Under this definition, the earliest evolutionary stage of the Jehol Biota is represented by the Huajiying Formation. The fossils are numerous, but also very well preserved — often including articulated skeletons, soft tissues, colour patterns, stomach contents, and twigs with leaves and flowers still attached.
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Edit The forests around the lakes were dominated by conifers including members of the podocarp Podocarpites , pine , araucaria Araucarites , and cypress families. There were also ginkgos , czekanowskialeans , bennettitaleans , ephedra Ephedrites , horsetails Equisetites , ferns , and mosses.
The leaves and needles of the trees show adaptations to a dry season, but some of the ferns and mosses are types that grow in very wet habitats. It is possible that the latter avoided dry conditions by growing very close to bodies of water. Archaefructus has been described as the earliest known flowering plant Angiosperm , and it is reconstructed as a water plant. Fossil preservation Edit The Yixian and Jiufotang Formations are called Lagerstatte , meaning that they have exceptionally good conditions for fossil preservation.
The fossils are numerous, but also very well preserved - often including articulated skeletons, soft tissues, color patterns, stomach contents, and twigs with leaves and flowers still attached. Zhonghe Zhou et al. The first is that the land animals and plants were washed into the lakes very gently, or were already in the lakes when they died.
They do not show the damage seen in fossils formed by large floods. Second, volcanic ash is commonly interbedded with lake sediments, and ashfalls seem to have quickly buried the fossilized organisms, created anoxic conditions around them, and prevented scavenging. Refuge and laboratory Edit Zhonghe Zhou et al. It is possible that northeast Asia was isolated for part of the Jurassic by the "Turgai Sea" which separated Europe from Asia at the time.
The Jehol Biota includes many species that were previously known only from the Late Jurassic or earlier. These "relict" species include the compsognathid dinosaur Sinosauropteryx , the anurognathid pterosaur Dendrorhynchoides , and even a primitive protomammal - a tritylodontid synapsid - from Early Cretaceous Japan; even though tritylodonts were previously thought to have gone extinct in the Middle Jurassic.
It also has the earliest and most primitive known members of groups that spread all around the world by the Late Cretaceous , including neoceratopsians , therizinosaurs , tyrannosaurs , and oviraptorids. Northeastern Asia may have been the center of diversification of these dinosaur groups. But the Jehol Biota was not entirely isolated, because it also includes animals which were known from all around the world at the same time, including discoglossid frogs , paramocellodid lizards , multituberculate mammals , enantiornithine birds, ctenochasmatid pterosaurs , iguanodontian ornithopods , titanosauriform sauropods , nodosaurid ankylosaurs , and dromaeosaurid theropods.
Diversity Edit The Jehol Biota is particularly noteworthy for the very high diversity of fossils and the very large numbers of individuals of each species that have been recovered. By now the Jehol Biota has produced fossils of plant mega- and microfossils, including the earliest angiosperms , charophytes and dinocysts , snails gastropods , clams bivalves , superabundant aquatic arthropods called conchostracans , ostracods , shrimps , insects , spiders , fish , frogs and salamanders amphibians , turtles , choristoderes , lizards squamates , pterosaurs , and dinosaurs including feathered dinosaurs , the largest mammals known from the Mesozoic , and a great diversity of birds including the earliest advanced birds, and the smallest and largest birds known from the Mesozoic.
Gu and defined the following species as typifying the Jehol Biota: gastropods : Bellamya clavilithiformis, B. Yumenia equimarginata, Limnocypridea tumulosa; insects : Ephemeropsis trisetalis, Mesolygaeus laiyangensis, Chironomaptera menlanura, Coptoclava longipoda, Clyptostemma xyphidle, Sinaeschuidia heishankouensis; fish : Lycoptera spp.
The Jehol Fossils