Tiaojishan Formation

Tiaojishan Formation Stratigraphic range: Bathonian-Oxfordian, 165–153 Ma PreЄ Є O S D C P T J K Pg N
Type	Geological formation
Sub-units	Daohugou bed
Underlies	Tuchengzi Formation
Overlies	Haifanggou Formation
Thickness	2420 meters
Lithology
Primary	Pyroclastic
Location
Region	Hebei, Inner Mongolia, & Liaoning
Country	China

The Tiaojishan Formation is a geological formation in Hebei and Liaoning, People's Republic of China, dating to the middle-late Jurassic period (Bathonian-Oxfordian stages). It is known for its fossil plants, and is made up mainly of pyroclastic rock interspersed with basic volcanic and sedimentary rocks. Previously, the Tiaojishan Formation was grouped together with the underlying Haifanggou Formation (also known as the Jiulongshan Formation) as a single "Lanqui Formation." Most researchers now agree that the Daohugou Bed, of formerly controversial dating, is a part of the Tiaojishan formation.

Geology

The geology of the Daohugou Bed is confusing because it is complex and does not conform; meaning that elements and layers of rock of different ages are mixed up together by folding and erosion and by volcanic activity. Liu et al. (2006) concluded that the rocks that bear the Daohugou Biota also include the Tiaojishan and Lanqi Formations. They demonstrated that the Jiulongshan Formation is older (Middle Jurassic), and that the Tuchengzi Formation is younger (Late Jurassic). However, many other researchers consider the Daohugou to be a part of the Jiulongshan Formation itself.

Fieldwork published in 2006 has also found that the beds are consistent over a large area; from western Liaoning into Ningcheng county of Inner Mongolia (Nei Mongol).

Age

Using Argon–argon dating, Wang and colleagues in 2005 dated part of the Tiaojishan Formation to about 160 million years ago, the beginning of the Oxfordian stage, the first stage of the Upper Jurassic epoch. In 2006, a study by Liu and colleagues used U-Pb zircon dating to conclude that the Tiaojishan Formation correlates with the Daohugou Beds, and the complete chronological range of this shared biota dates to between 168 and 164/152 Ma ago. A subsequent study, published in 2008, refined the age range of the formation further, finding that the lower boundary of the Tiaojishan was formed 165 Ma ago, and the upper boundary somewhere between 156-153 Ma ago.

Daohugou bed

The age of the Daohugou bed has been debated, and a number of studies, using different methodologies, have reached conflicting conclusions. Various papers have placed the fossils here as being anywhere from the Middle Jurassic period (169 million years ago) to the Early Cretaceous period (122 ma). One of the first studies on the age of the Daohugou beds, published in 2004 by He et al., found them to be Early Cretaceous, only a few million years older than the overlying Jehol beds of the Yixian Formation. The 2004 study primarily used Argon–argon dating of a tuff within the Daohugou Beds to determine its age.

However, subsequent studies cast doubt on this relatively recent age. In a 2006 study, Gao & Ren criticized He et al. for not including enough specifics and detail in their paper, and also took issue with their radiometric dating of the Daohugou tuff. The tuff, Gao and Ren argued, contains crystals with a variety of diverse radiometric ages, some up to a billion years old, so using dates from only a few of these crystals could not determine the overall age of the deposits. Gao and Ren went on to defend a Middle Jurassic age for the beds based on biostratigraphy (the use of index fossils), and the bed's relationship to a layer that is known to mark the Middle Jurassic-Late Jurassic boundary.

Another study, published in 2006 by Wang et al., argued that the 159-164 million years old Tiaojishan Formation underlies, rather than overlies, the Daohugou Beds. Unlike the earlier study by Gao and Ren, Wang et al. found an overall similarity between the fossil animals found in the Daohugou Beds and those from the Yixian Formation. The authors stated that

"vertebrate fossils such as Liaoxitriton, Jeholopterus and feathered maniraptorans show much resemblance to those of the Yixian Formation. In other words, despite the absence of Lycoptera, a typical fish of the Jehol Biota, the Daohugou vertebrate assemblage is closer to that of the Early Cretaceous Jehol Biota than to any other biota."

Wang et al. concluded that the Daohugou probably represents the earliest evolutionary stages of the Jehol Biota, and that it "belongs to the same cycle of volcanism and sedimentation as the Yixian Formation of the Jehol Group." However, a later study by Ji et al. argued that the key indicator of the Jehol biota are the index fossils Peipiaosteus and Lycoptera. Under this definition, the earliest evolutionary stage of the Jehol Biota is represented by the Huajiying Formation, and the Daohugou Formation is excluded due to the absence of Lycoptera fossils. Later in 2006, Liu et al. published their own study of the age of the Daohugou beds, this time using Zircon Uranium-lead 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. A 2012 study by Gao and Shubin agreed with this assessment, and reported an Argon–argon date of 164 plus or minus 4 million years ago for the Daohugou horizon.

Climate

Based on the plant life present in the Tiaojishan Formation, Wang Yongdong and colleagues determined that the climate in Liaoning during the mid Jurassic would have been subtropical to temperate, warm and humid.

Fauna

Beautifully preserved fossils of dinosaurs, pterosaurs, salamanders, insects, arachnids and other invertebrates, conifers, ginkgoes, cycads, horsetails, and ferns, and even the earliest known gliding mammal (Volaticotherium) and an aquatic protomammal (Castorocauda) have been discovered in these rocks. These organisms were part of the Daohugou Biota, which was the ecosystem of that Jurassic time. The tuffaceous composition of some rock layers show that this was a volcanic area, occasionally experiencing heavy ashfalls from eruptions. The landscape then was dominated by mountain streams and deep lakes surrounded by forests of gymnosperm trees. Some authors have concluded that the Daohugou Biota is an early stage of the Jehol Biota, while recent work has demonstrated that the two are distinct.

The forests of the Daohugou biota grew in a humid, warm - temperate climate and were dominated by gymnosperm trees. There were ginkgopsids like Ginkoites, Ginkgo, Baiera, Czekanowskia, and Phoenicopsis. There were also conifers like Pityophyllum, Rhipidiocladus, Elatocladus, Schizolepis, and Podozamites. Also, Lycopsids like Lycopodites and Sellaginellities, horsetails (Sphenopsida) like Equisetum, cycads like Anomozamites, and ferns (Filicopsida) like Todites and Coniopteris.

Salamanders

Salamanders of the Tiaojishan Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Beiyanerpeton	B. jianpingensis	Liaoning			A salamandroid known from an almost complete and articulated skeleton exposed in ventral view.	Chunerpeton
Chunerpeton	C. tianyiensis				A cryptobranchoid measuring 18 centimeters in length.
Jeholotriton	J. paradoxus				A cryptobranchoid with a strange skull morphology, at first believed to come from the Early Cretaceous.
Liaoxitriton	L. daohugouensis				A little-known cryptobranchoid.
Pangerpeton	P. sinensis				A cryptobranchoid characterized by its short trunk (only 14 presacrals) and short and wide head, giving a fat body shape, from which the genus name was derived ("Pang" means fat in Chinese).

Pterosaurs

Pterosaurs of the Tiaojishan Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Archaeoistiodactylus	A. linglongtaensis	Liaoning			An breviquartossan known from an incomplete skeleton with a partial skull and lower jaw.	File:Darwinopterus EF.jpg Darwinopterus modularis File:Jeholopterus BW.jpg Jeholopterus File:Wukongopterus NT.jpg Wukongopterus
Changchengopterus	C. pani	Hebei			A pterodactyliform known only from a single specimen of a young juvenile, measuring 475 millimeters (18.7 inches) in wingspan.
Daohugoupterus	D. delicatus	Inner Mongolia		One specimen	A relatively basal pterosaur known from a partial skeleton with soft tissue impressions.
Darwinopterus	D. modularis	Liaoning			A wukongopterid named after Charles Darwin. The type species, D. modularis was the first known pterosaur to display features of both long-tailed rhamphorhynchoids and short-tailed pterodactyloids, and was described as a transitional fossil between the two groups. Darwinopterus specimens have also been reported to show several differences between males and females, with the males having distinctive crests on their heads. They are known to have laid their eggs on the ground, and may have also not shown that much for parental care.
	D. linglongtaensis
	D. robustodens
Dendrorhynchoides	D. mutoudengensis	Hebei		One specimen	An asiaticognathine anurognathid, originally thought to be from the Early Cretaceous, with a wingspan that is about 40 centimeters, making it one of the smallest known pterosaurs.
Fenghuangopterus	F. lii	Liaoning			A scaphognathine rhamphorhynchid similar to other scaphognathines in its short, blunt skull with a large antorbital fenestra, and widely spaced, vertically oriented teeth (as opposed to the horizontally-oriented teeth of other rhamphorhynchids).
Jeholopterus	J. ninchengensis	Inner Mongolia		Several specimens	An asiaticognathine anurognathid preserved with pycnofibres and skin remains.
Jianchangnathus	J. robustus	Liaoning			A scaphognathine rhamphorhynchid known from a single fossil skeleton.
Jianchangopterus	J. zhaoianus	Liaoning			A scaphognathine rhamphorhynchid known from a nearly complete skeleton with the skull preserved.
Pterorhynchus	P. wellnhoferi	Inner Mongolia	Daohugou bed	One specimen	A darwinopteran with a tall crest on its head and an elongated skull 11.8 centimeters (4.65 inches) long, a long tail and a wingspan of about 85 centimeters (33.46 inches). It was originally believed to be a rhamphorhynchid.
Qinglongopterus	Q. guoi	Liaoning			A rhamphorhynchine rhamphorhynchid known from only one specimen that includes a skeleton with a skull.
Wukongopterus	W. lii	Liaoning	Daohugou bed	One specimen	A wukongopterid unusual for having both an elongate neck and a long tail. Its wingspan is estimated at 730 millimeters (29 inches).

Dinosaurs

Dinosaurs of the Tiaojishan Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Anchiornis	A. huxleyi	Liaoning		Several specimens	A primitive avialan at first believed to be a troodont. Given the exquisite preservation of one of the first specimen's fossils, Anchiornis became the first dinosaur species for which almost the entire life coloration could be determined. Most of the body feathers of Anchiornis were gray and black. The crown of head feathers was mainly rufous with a gray base and front, and the face had rufous speckles among predominantly black head feathers. The wing and hind leg feathers were white with black tips. The coverts were gray, contrasting the mainly white main wings. The larger coverts of the wing were also white with gray or black tips, forming rows of darker dots along mid-wing. These took the form of dark stripes or even rows of dots on the outer wing (primary feather coverts) but a more uneven array of speckles on the inner wing (secondary coverts). The shanks of the legs were gray other than the long leg feathers, and the feet and toes were black. It was 34 centimeters (13 inches) and weighed only 110 grams (3.9 ounces).	Anchiornis File:Aurornis.jpg Aurornis File:Eosinopteryx.jpg Eosinopteryx File:Epidexipteryx (long fingers).JPG Epidexipteryx File:Scansor chick.png Scansoriopteryx File:Tianyulong BW.jpg Tianyulong File:Xiaotingia .jpg Xiaotingia Yi
Aurornis	A. xui	Liaoning		One specimen	A primitive avialan that may be the most basal avialan dinosaur known to date, and it is one of the earliest avialans found to date. The fossil evidence for the animal predates that of the Archaeopteryx, often considered the earliest bird species, by about 10 million years. Aurornis was roughly the size of a modern pheasant, with a length of 50 centimeters (20 inches). Its leg bones were similar to those of Archaeopteryx, but overall its anatomy was more primitive.
Eosinopteryx	E. brevipenna	Liaoning		One specimen	A basal paravian (probably an avialan), at first believed to be a troodont, known from a single fossil specimen representing the nearly complete skeleton of a subadult or adult individual. The specimen is very small for a non-avialan dinosaur, measuring about 30 centimeters (12 inches, or 1 foot) long.
Epidexipteryx	E. hui	Inner Mongolia	Daohugou beds	One specimen	A scansoriopterygid known from a well-preserved partial skeleton, measuring 25 centimeters (10 inches) in length (44.5 centimeters or 17.5 inches including the incomplete tail feathers), that includes four long feathers on the tail, composed of a central rachis and vanes. However, unlike in modern-style rectrices, the vanes were not branched into individual filaments but made up of a single ribbon-like sheet. Epidexipteryx also preserved a covering of simpler body feathers, composed of parallel barbs as in more primitive feathered dinosaurs. However, the body feathers of Epidexipteryx are unique in that some appear to arise from a "membranous structure" at the base of each feather. It has been suggested that this may represent a stage in the evolution of the feather. Epidexipteryx represents the earliest known example of ornamental feathers in the fossil record.
Pedopenna	P. daohugouensis	Inner Mongolia	Daohugou beds	One specimen	A primitive avialan that is possibly older than Archaeopteryx, though the age of the Daohugou Beds is debated. It probably measured 1 meter (3 feet) or less in length, but since this species is only known from the hind legs, the actual length is difficult to estimate.
Scansoriopteryx	S. heilmanni	Liaoning	Exact provenance of type specimen unknown, most likely from the Daohugou Beds	One or two specimens	A sparrow-sized scansoriopterygid known from a juvenile specimen.
Tianyulong	T. confuciusi	Liaoning			A heterodontosaur that was initially reported as being from the Early Cretaceous Jehol group. The fossil was collected at a locality transliterated as Linglengta or Linglongta. Lu et al., 2010, reported that these beds were actually part of the Tiaojishan Formation, dating from the Late Jurassic period. Tianyulong has a row of long, filamentous integumentary structures on the back, tail and neck of the specimen, similar to the feathers found in certain theropods (this suggests that all heterodontosaurs may have had these filaments). The holotype is from a subadult individual that probably measured 70 centimeters in length based on the proportions of the related Southern African species Heterodontosaurus.
Xiaotingia	X. zhengi	Liaoning		One specimen	A primitive avialan originally thought to be either a dromaeosaur or a troodont.
Yi	Y. qi	Hebei	Daohugou beds	One specimen	A gliding scansoriopterygid, weighing about 380 grams (0.84 pounds), that, like other scansoriopterygids, possessed an unusual, elongated third finger, that (in the case of Yi) helped to support a membranous gliding plane made of skin. The planes of Yi were also supported by a long, bony strut attached to the wrist. This modified wrist bone and membrane-based plane is unique among all known dinosaurs, and might have resulted in wings similar in appearance to those of bats. This also leads to the hypothesis that the other two genera of scansoriopterygids also had gliding membranes, but this is yet to be proven official.

Lizards

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Lepidosaurs (lizards and relatives) of the Daohugou Beds
Genus	Species	State	Abundance	Notes	Images
Unnamed lizard		Inner Mongolia	One specimen	A new lizard with relatively short forelimbs
Unnamed lizard		Inner Mongolia	One specimen	A lizard with long hind limbs and a narrow body

Cynodonts

Cynodonts of the Tiaojishan Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Agilodocodon	A. scansorius	Inner Mongolia	Daohugou bed		A shrew-sized, arboreal docodont that is known to be one of the earliest tree-climbing mammaliaforms. It measured approximately 13 centimeters from head to tail and weighed about 27 grams. Its appearance was similar to a squirrel, with a long snout, curved, horny claws and flexible ankle and wrist joints typical of modern arboreal mammals. The front teeth were spade-like, indicating that Agilodocodon could gnaw tree bark and consume gum or sap.	Castorocauda Juramaia File:Volaticotherium.jpg Volaticotherium
Arboroharamiya	A. jenkinsi	Liaoning		One specimen	An arboreal, prehensile-tailed euharamiyid haramiyidan that was the largest known haramiyidan, estimated to have weighed about 354 grams. Arboroharamiya is unlike any modern mammal in having a lower jaw that can move up, down, and backward, but not forward. It has a rodent-like dentition with enlarged incisors and molars and no canines.
Castorocauda	C. lutrasimilis	Inner Mongolia	Daohugou bed	One specimen	A semiaquatic docodontid that was highly specialized, with adaptations evolved convergently with those of modern semiaquatic mammals such as beavers, otters, and platypuses. The animal probably weighed about 500-800 grams (1 pound to nearly 2 pounds) and grew to at least 42.5 centimeters (17 inches) in length. This makes it the largest mammaliaform (including true mammals) of the Jurassic (the previous record holder being Sinoconodon).
Docofossor	D. brachydactylus	Hebei		One specimen	A docodontid specialized for a subterranean burrowing lifestyle. The skeletal structure and body proportions are strikingly similar to the golden mole. It was at least 9 centimeters long, exempting the tail, and weighed at least 9 grams, or perhaps 16 grams.
Juramaia	J. sinensis	Liaoning		One specimen	A small, shrew-like eutherian with a body length approximately 70-100 millimeters. The discovery of Juramaia provides new insight into the evolution of placental mammals by showing that their lineage diverged from that of the metatheres 35 million years earlier than previously thought. Furthermore, its discovery fills gaps in the fossil record and helps to calibrate modern, DNA-based methods of dating the evolution. Based on climbing adaptations found in the forelimb bones, it has been suggested that the basal stock of eutherians was arboreal.
Megaconus	M. mammaliaformis	Inner Mongolia	Daohugou bed	One specimen	An eleutherodontid haramiyidan thought to have been a herbivore that lived on the ground, having a similar posture to modern-day armadillos and rock hyraxes. Megaconus is estimated to have weighed about 250 grams (8.8 ounces).
Rugosodon	R. eurasiaticus	Liaoning	Daxishan site	One specimen	A paulchoffatiid multituberculate that is the oldest so far described in the multituberculates. It strongly resembled a small rodent (like a rat or a chipmunk). It is estimated to have weighed between 65-80 grams, about that of an average chipmunk.
Volaticotherium	V. antiquum	Inner Mongolia	Daohugou bed	One specimen	A gliding, flying squirrel-like triconodont with a specialized gliding membrane. The teeth of Volaticotherium were highly specialized for eating insects, and its limbs were adapted to living in trees. The gliding membrane was insulated by a thick covering of fur, and was supported by the limbs as well as the tail. The discovery of Volaticotherium provided the earliest-known record of a gliding mammal, and provided further evidence of mammalian diversity during the Mesozoic Era.

Arthropods

The following orders are represented in the formation; Ephemeroptera, Odonata, Plecoptera, Blattodea, Orthoptera, Hemiptera, Neuroptera, Coleoptera, Hymenoptera, and Diptera.

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Arthropods of the Daohugou Beds
Genus	Species	State	Abundance	Notes	Images
Ahirmoneura	A. neimengguensis	Inner Mongolia		A tangle-veined fly
Archirhagio	A. striatus			Archisargid flies
	A. zhangi	Inner Mongolia
Archisargus	A. spurivenius			Archisargid flies
	A. strigatus
Calosargus	C. (Calosargus) antiquus			Archisargid flies
	C. (C.) bellus
	C. (C.) daohugouensis
	C. (C.) hani
	C. (C.) tenuicellulatus
	C. (C.) validus
	C. (Pterosargus) sinicus	Inner Mongolia
Daohugocorixa	D. vulcanica			A water boatman
Fuyous	F. gregarious			A mayfly
Eoplectreurys	E. gertschi		1 Specimen	A plectreurid spider
Homocatabrycus	H. liui			A schizophorid flying water beetle
Jurassinemestrinus	J. orientalis	Inner Mongolia		A Nemestrinoid fly
Menopraesagus	M. explanatus			Schizophorid flying water beetles
	M. oxycerus
	M. grammicus
Meoslova	M. daohugouensis			An archisargid fly
Mostovskisargus	M. portentosus	Inner Mongolia		Archisargid flies
	M. signatus	Inner Mongolia
Mongolarachne	M. jurassica		2 Specimens	An araneomorph spider
Shantous	S. lacustris			A mayfly
Sinoschizala	S. darani			A schizophorid flying water beetle

Other invertebrates

An indeterminate aeschnoid (insect) species is known from Liaoning.

Genus	Species	Province	Stratigraphic Position	Abundance	Notes
Darwinula	D. impudica	Liaoning		An ostracod
	D. magna	Liaoning		An ostracod
	D. sarytirmenensis	Liaoning		An ostracod
Shaanxiconcha	S. cliovata	Liaoning		A bivalve

Flora

Survey based on Wang et al. 2006 unless otherwise noted.

Bennettitales

Cycad-like plants, the most abundant plant group in the formation. 27 species in 11 genera.

Plants of the Tiaojishan Formation.
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Anomozamites
Bennetticarpus
Cycadolepis
Jacutiella
Pteriophyllum
Ptilophyllum
Williamsonia
Williamsoniella
Zamiophyllum
Zamites

Ginkgoales

Prehistoric ginkgo trees, common, with 11 species present in 6 genera.

Plants of the Tiaojishan Formation.
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Ginkgo
Ixostrobus
Phoenicopsis
Sphenobaiera
Solenites

Pinophyta

Conifers, 5 species present in 4 genera.

Plants of the Tiaojishan Formation.
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Pityocladus
Pityophyllum
Podizamites
Schizolepis
Yuccites

Pteridophyta

Leptosporangiate ferns, represented by 17 species in 8 genera, are the second most abundant plant type in the formation.

Plants of the Tiaojishan Formation.
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Cladophlebis spp.					Ferns
Coniopteris					Dicksoniaceae Tree ferns.
Dicksonia	D. changeyingziensis				Dicksoniaceae Tree ferns.
	D. charielsa
Eboracia					Dicksoniaceae Tree ferns.
Hausmannia	H. shebudaiensis			Uncommon.	A dipterid fern.
Marattia	M. hoerenensis			Uncommon.	A marattiopsid fern.
Raphaelia	R. stricta				A fern.
Toadites	T. denticulata				"Flowering ferns."
	T. williamsonii				"Flowering ferns."

Other plants

Cycads, fairly diverse, with 10 species present in 2 genera.

Plants of the Tiaojishan Formation.
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Ctenis					Cycadales.
Equisetum					Horsetails.
Neocalamites					Horsetails.
Nilssonia					Cycadales.
Hepacitities	H. shebudaiensis			Uncommon.	A bryophyte.
Taeniopteris sp.				Uncommon.