Jehol Biota
Encyclopedia
The Jehol Biota includes all the living organisms - the ecosystem
- of northeastern China between 133 to 120 million years ago. This is the Lower Cretaceous ecosystem which left fossils in the Yixian Formation
and Jiufotang Formation
. It is also believed to have left fossils in the Sinuiju
series of North Korea
. The ecosystem in the Lower Cretaceous was dominated by wetlands and numerous lakes (not rivers, deltas, or marine habitats). Rainfall was seasonal, alternating between semiarid, and mesic
conditions. The climate was temperate
. The Jehol ecosystem was interrupted periodically by ash eruptions from volcanoes to the west. The word "Jehol
" now said to refer to a mythical land of the past in Chinese folklore, was the name given during Japanese occupation of the former Rehe Province.
and Lycoptera. Under this definition, the earliest evolutionary stage of the Jehol Biota is represented by the Huajiying Formation
.
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.. (2003) deduced two things from this. 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.
, the Jehol Biota includes a mixture of advanced and ancient species, and also of species found only in the Jehol and others found all around the world. 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, therizinosaur
s, 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 frog
s, paramocellodid lizard
s, multituberculate mammal
s, enantiornithine birds, ctenochasmatid pterosaur
s, iguanodont
ian ornithopod
s, titanosauriform sauropods, nodosaurid ankylosaurs, and dromaeosaurid theropods.
The Jehol Biota has produced fossils of plant mega- and microfossils, including the earliest angiosperms, charophytes and dinocyst
s, snails (gastropods), clams (bivalves), superabundant aquatic arthropods called conchostracans, ostracods, shrimp
s, insects, spiders, fish
, frogs and salamanders (amphibian
s), turtle
s, choristoderes, lizards (squamates), pterosaur
s, and dinosaurs including feathered dinosaurs
, the largest mammal
s 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.
The forests around the lakes were dominated by conifers including members of the podocarp (Podocarpites), pine
, araucaria
(Araucarites), and cypress
families. There were also ginkgo
s, czekanowskialeans, bennettitaleans, ephedra
(Ephedrites), horsetails (Equisetites), fern
s, and moss
es. 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.
Gu (1983 and 1995) defined the following species as typifying the Jehol Biota:
See
(1923) defined as the fossil assemblage typified by numerous fossils of the conchostraca
n Eosestheria, the mayfly
Ephemeropsis, and the Teleost fish Lycoptera
. Thus it was sometimes called "EEL".
The Jehol group was defined by Gu (1962 and 1983) as a group of geological formations including the Jehol Coal-bearing Beds, the Jehol Oil Shale Beds, and the Jehol Volcanic Rocks. By now the group includes, in ascending order, the Yixian Formation (including the Jingangshan, Tuhulu, Jianchang, Lower Volcanic and Volcanic Rock formations), the Jiufotang Formation
(including the Shahai Formation) and the Fuxin Formation (including the Binggou, Haizhou and Upper Volcanic formations). Chiappe et al. argued in 1999 that the lower beds of the Yixian were best subdivided into a separate formation, the Chaomidianzi Formation, with a type locality at the village of Sihetun, approximately 25 km south of Beipiao City. However, this classification has fallen out of favor, and the Chaomidianzi Formation is disused as a synonym of the Jianshangou Bed of the Yixian Formation.
In 2008, Ji et al. argued that these traditional definitions of the Jehol Biota arbitrarily excluded earlier fossil beds that clearly represent the first evolutionary stages of the later faunas, even though lower beds also had representatives of Ephemeropsis and Lycoptera. They argued that the boundaries of the biota should rather be set based on the distinctive large-scale sequences of volcanism which produced the strata, with the upper boundary set at the Shahai and Fuxin formations and the lower boundary at the Zhangjiakou Formation. Along with this sedimentary correlation, they noted that the best index fossils to identify the biota are Peipiaosteus
and Lycoptera. Under this definition, the earliest stage of the Jehol Biota is represented by the Huajiying Formation
.
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
- of northeastern China between 133 to 120 million years ago. This is the Lower Cretaceous ecosystem which left fossils in the Yixian Formation
Yixian Formation
The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans 11 million years during the early Cretaceous period...
and Jiufotang Formation
Jiufotang Formation
The Jiufotang Formation is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms. . It is a member of the Jehol group. The exact age of the Jiufotang has been debated for years, with...
. It is also believed to have left fossils in the Sinuiju
Sinuiju
Sinŭiju is a city in North Korea, neighboring with Dandong City, China via international border and is the capital of North P'yŏngan Province...
series of North Korea
North Korea
The Democratic People’s Republic of Korea , , is a country in East Asia, occupying the northern half of the Korean Peninsula. Its capital and largest city is Pyongyang. The Korean Demilitarized Zone serves as the buffer zone between North Korea and South Korea...
. The ecosystem in the Lower Cretaceous was dominated by wetlands and numerous lakes (not rivers, deltas, or marine habitats). Rainfall was seasonal, alternating between semiarid, and mesic
Mesic habitat
In ecology, a mesic habitat is a type of habitat with a moderate or well-balanced supply of moisture, e.g., a mesic forest, a temperate hardwood forest, or dry-mesic prairie. Compared to a dry habitat, a mesic habitat is moister....
conditions. The climate was temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
. The Jehol ecosystem was interrupted periodically by ash eruptions from volcanoes to the west. The word "Jehol
Jehol
Jehol could mean either a province or a city:* Jehol Province, former province in northeastern China* Chengde, the capital of above provinceNamed after the province:* Jehol Biota* Jeholodens* Jeholopterus* Jeholornis* Jeholosaurus...
" now said to refer to a mythical land of the past in Chinese folklore, was the name given during Japanese occupation of the former Rehe Province.
Origin
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 2006, Wang et al. found an overall similarity between the fossil animals found in the Daohugou Beds and the "Jehol Biota" from the Yixian Formation. Several other research teams, including Liu et al., have attempted to disprove this reasoning by using Zircon U-Pb dating on the volcanic rocks overlying and underlying salamander-bearing layers (salamanders are often used as index fossils). Liu et al. found that the beds formed between 164-158 million years ago, in the Middle to Late Jurassic. Later, Ji et al. argued that the key indicator of the Jehol biota are the index fossils PeipiaosteusPeipiaosteus
Peipiaosteus is an extinct genus of prehistoric bony fish. This is a very rare species of sturgeon from Jiufotang Formation, Pani Lake, Liaoning Province, China. -See also:* Prehistoric fish* List of prehistoric bony fish...
and Lycoptera. Under this definition, the earliest evolutionary stage of the Jehol Biota is represented by the Huajiying Formation
Huajiying Formation
The Huajiying Formation is a geological formation in Hebei, People's Republic of China. Known for its fossils including primitive birds, the age of the ormation is uncertain. It may represent an early portion of the Jehol Biota, dating to somewhere in the early Cretaceous or late Jurassic periods...
.
Fossil preservation
The YixianYixian
Yixian may refer to:*Yi County, Anhui, in China*Yi County, Hebei, in China*Yi County, Liaoning, in China*Yixian Formation, a geological formation in Liaoning Province*Empress Yixian, Liang Nüying , Chinese empress during the Han Dynasty...
and Jiufotang Formations are called Lagerstatte
Lagerstätte
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....
, 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.. (2003) deduced two things from this. 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
Hypoxia (environmental)
Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...
conditions around them, and prevented scavenging.
Refuge and laboratory
Zhonghe Zhou et al.. (2003) noted that, for the Early CretaceousEarly Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
, the Jehol Biota includes a mixture of advanced and ancient species, and also of species found only in the Jehol and others found all around the world. It is possible that northeast Asia was isolated for part of the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
by the "Turgai Sea
Turgai Sea
The Turgai Sea or Turgai Strait, also known as the West Siberian Sea, was a large shallow body of salt water of the Mesozoic and Cenozoic Eras...
" which separated Europe from Asia at the time.
The Jehol Biota includes many species that were previously known only from the Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
or earlier. These "relict" species include the compsognathid dinosaur Sinosauropteryx
Sinosauropteryx
Sinosauropteryx was the first genus of dinosaur outside of Avialae to be found with evidence of feathers. They were covered with "furry" coats of very simple filament-like feathers...
, the anurognathid
Anurognathid
The Anurognathidae were a group of small pterosaurs, with short tails or tailless, that lived in Europe and Asia during the Jurassic and early Cretaceous periods...
pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
Dendrorhynchoides
Dendrorhynchoides
Dendrorhynchoides was a genus of anurognathid pterosaur from the Early Cretaceous Yixian Formation, near Beipiao, Chaoyang, Liaoning, China...
, and even a primitive protomammal - a tritylodontid synapsid
Synapsid
Synapsids are a group of animals that includes mammals and everything more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having an opening low in the skull roof behind each eye, leaving a bony arch beneath each, accounting for their name...
- from Early Cretaceous Japan; even though tritylodonts were previously thought to have gone extinct in the Middle Jurassic
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
. It also has the earliest and most primitive known members of groups that spread all around the world by the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
, including neoceratopsians, therizinosaur
Therizinosaur
Therizinosaurs are theropod dinosaurs belonging to the clade Therizinosauria. Therizinosaur fossils have been found in Early through Late Cretaceous deposits in Mongolia, the People's Republic of China and Western North America...
s, 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 frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
s, paramocellodid lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s, multituberculate mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, enantiornithine birds, ctenochasmatid pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
s, iguanodont
Iguanodont
Iguanodonts were herbivorous dinosaurs that lived from the mid-Jurassic to Late Cretaceous. Some members include Camptosaurus, Callovosaurus, Iguanodon, Ouranosaurus, and the hadrosaurids or "duck-billed dinosaurs". Iguanodonts were one of the first groups of dinosaurs to be found...
ian ornithopod
Ornithopod
Ornithopods or members of the clade Ornithopoda are a group of ornithischian dinosaurs that started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American...
s, titanosauriform sauropods, nodosaurid ankylosaurs, and dromaeosaurid theropods.
Diversity
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.The Jehol Biota has produced fossils of plant mega- and microfossils, including the earliest angiosperms, charophytes and dinocyst
Dinocyst
Dinocysts are produced by around 10% of living Dinoflagellates as a dormant zygotic stage of their lifecycle. The next-generation Dinoflagellate exits the cyst via the archaeopyle, a hole which may take the form of the removal of the apex of the cyst , or the removal of one of the tabulæ...
s, snails (gastropods), clams (bivalves), superabundant aquatic arthropods called conchostracans, ostracods, shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
s, insects, spiders, fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, frogs and salamanders (amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s), turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s, choristoderes, lizards (squamates), pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
s, and dinosaurs including feathered dinosaurs
Feathered dinosaurs
The realization that dinosaurs are closely related to birds raised the obvious possibility of feathered dinosaurs. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly non-avialan dinosaur fossils were discovered with preserved feathers...
, the largest mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s known from the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
, and a great diversity of birds including the earliest advanced birds, and the smallest and largest birds known from the Mesozoic.
The forests around the lakes were dominated by conifers including members of the podocarp (Podocarpites), pine
Pine
Pines are trees in the genus Pinus ,in the family Pinaceae. They make up the monotypic subfamily Pinoideae. There are about 115 species of pine, although different authorities accept between 105 and 125 species.-Etymology:...
, araucaria
Araucaria
Araucaria is a genus of evergreen coniferous trees in the family Araucariaceae. There are 19 extant species in the genus, with a highly disjunct distribution in New Caledonia , Norfolk Island, eastern Australia, New Guinea, Argentina, Chile, and southern Brazil.-Description:Araucaria are mainly...
(Araucarites), and cypress
Cypress
Cypress is the name applied to many plants in the cypress family Cupressaceae, which is a conifer of northern temperate regions. Most cypress species are trees, while a few are shrubs...
families. There were also ginkgo
Ginkgo
Ginkgo , also spelled gingko and known as the Maidenhair Tree, is a unique species of tree with no close living relatives...
s, czekanowskialeans, bennettitaleans, ephedra
Ephedra
Ephedra refers to the plant Ephedra sinica. E. sinica, known in Chinese as ma huang , has been used in traditional Chinese medicine for 5,000 years for the treatment of asthma and hay fever, as well as for the common cold...
(Ephedrites), horsetails (Equisetites), fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s, and moss
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
es. 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
Archaefructus
Archaefructus is an extinct genus of herbaceous aquatic seed plants with 3 known species. Fossil material assigned to this genus originates from the Yixian Formation in northeastern China, originally dated as late Jurassic but now thought to be approximately 125 million years old, or early...
has been described as the earliest known flowering plant (Angiosperm), and it is reconstructed as a water plant.
Gu (1983 and 1995) defined the following species as typifying the Jehol Biota:
- gastropods: Bellamya clavilithiformis, B. fengtienensis, Probaicalia gerassimovi, P. spp., Viviparus, Galba, Hydrobia;
- bivalves: Arguniella cf. ventricosa (=Ferganoconcha linguanense)-Sphaerium (Sphaerium) anderssoni (=Sphaerium jeholensis) fossil group, Nakamuranaia, Weichangella;
- conchostracaConchostracaClam shrimp are a taxon of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant, and known from the fossil record, from at least the Devonian period and perhaps before...
ns: Eosestheria-Diestheria-Liaoningestheria or Eosestheria fossil group, Fengninggrapta, Yanjiestheria, Pseudestherites, Orthestheria; - ostracodOstracodOstracoda is a class of the Crustacea, sometimes known as the seed shrimp because of their appearance. Some 65,000 species have been identified, grouped into several orders....
s: Cypridea sulcata, C. vitimensis, C. yumenensis, C. koskulensis, C. tumescens-C. dunkeri-C. granulosa assemblage, C. (Yumenia) equimarginata, Limnocypridea tumulosa; - insectInsectInsects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s: Ephemeropsis trisetalis, Mesolygaeus laiyangensis, Chironomaptera menlanura, Coptoclava longipoda, Clyptostemma xyphidle, Sinaeschuidia heishankouensis; - fishFishFish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
: Lycoptera spp., Peipiaosteus, Sinamia, Haizhoulepis; - reptileReptileReptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s: Monjurosuchus splendens (including Rhynchosaurus orientalis), Yabeinosaurus tenuis, Luanpingosaurus, PsittacosaurusPsittacosaurusPsittacosaurus is a genus of psittacosaurid ceratopsian dinosaur from the Early Cretaceous Period of what is now Asia, about 130 to 100 million years ago. It is notable for being the most species-rich dinosaur genus...
; - and mammalMammalMammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s: Endotherium niinomi.
See
- Daohugou Biota
- Yixian FormationYixian FormationThe Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans 11 million years during the early Cretaceous period...
- Jiufotang FormationJiufotang FormationThe Jiufotang Formation is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms. . It is a member of the Jehol group. The exact age of the Jiufotang has been debated for years, with...
Study
The name "Jehol Biota" was first published by Gu (1962), but was in use by geologists and paleontologists by 1959. This term replaced the former "Jehol Fauna", which Amadeus William GrabauAmadeus William Grabau
Amadeus William Grabau was a German-American paleontologist and geologist who was born on January 9, 1870 in Cedarburg, Wisconsin in the United States and died on March 20, 1946 in Peking, China. He was employed as faculty at MIT and Rensselaer Polytechnic Institute...
(1923) defined as the fossil assemblage typified by numerous fossils of the conchostraca
Conchostraca
Clam shrimp are a taxon of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant, and known from the fossil record, from at least the Devonian period and perhaps before...
n Eosestheria, the mayfly
Mayfly
Mayflies are insects which belong to the Order Ephemeroptera . They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies...
Ephemeropsis, and the Teleost fish Lycoptera
Lycoptera
Lycoptera is a genus of fish that lived from the late Jurassic to Cretaceous periods in present-day China, Korea, Mongolia and Siberia. It is known from abundant fossils representing sixteen species, and is an important index fossil used to date geologic formations in China...
. Thus it was sometimes called "EEL".
The Jehol group was defined by Gu (1962 and 1983) as a group of geological formations including the Jehol Coal-bearing Beds, the Jehol Oil Shale Beds, and the Jehol Volcanic Rocks. By now the group includes, in ascending order, the Yixian Formation (including the Jingangshan, Tuhulu, Jianchang, Lower Volcanic and Volcanic Rock formations), the Jiufotang Formation
Jiufotang Formation
The Jiufotang Formation is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms. . It is a member of the Jehol group. The exact age of the Jiufotang has been debated for years, with...
(including the Shahai Formation) and the Fuxin Formation (including the Binggou, Haizhou and Upper Volcanic formations). Chiappe et al. argued in 1999 that the lower beds of the Yixian were best subdivided into a separate formation, the Chaomidianzi Formation, with a type locality at the village of Sihetun, approximately 25 km south of Beipiao City. However, this classification has fallen out of favor, and the Chaomidianzi Formation is disused as a synonym of the Jianshangou Bed of the Yixian Formation.
In 2008, Ji et al. argued that these traditional definitions of the Jehol Biota arbitrarily excluded earlier fossil beds that clearly represent the first evolutionary stages of the later faunas, even though lower beds also had representatives of Ephemeropsis and Lycoptera. They argued that the boundaries of the biota should rather be set based on the distinctive large-scale sequences of volcanism which produced the strata, with the upper boundary set at the Shahai and Fuxin formations and the lower boundary at the Zhangjiakou Formation. Along with this sedimentary correlation, they noted that the best index fossils to identify the biota are Peipiaosteus
Peipiaosteus
Peipiaosteus is an extinct genus of prehistoric bony fish. This is a very rare species of sturgeon from Jiufotang Formation, Pani Lake, Liaoning Province, China. -See also:* Prehistoric fish* List of prehistoric bony fish...
and Lycoptera. Under this definition, the earliest stage of the Jehol Biota is represented by the Huajiying Formation
Huajiying Formation
The Huajiying Formation is a geological formation in Hebei, People's Republic of China. Known for its fossils including primitive birds, the age of the ormation is uncertain. It may represent an early portion of the Jehol Biota, dating to somewhere in the early Cretaceous or late Jurassic periods...
.