Xitaizi locality lower part of Yixian Formation in Ningcheng Chifeng Inner Mongolia

The most notable among these localities are Sihetun, Jianshangou, Zhangjiagou, Huangbanjigou, Hengdaozi, Libalanggou, Heitizigou, etc. Fossil-bearing beds comparable to the Jianshangou Bed are also found in other basins of western Liaoning, northern Hebei and southeastern Inner Mongolia, including Shangyuan Bed in Beipiao, and Zhuanchengzi Beds in Yixian County.

The Jianshangou Bed represents 2~3 sedimentary cycles of coastal lake, shallow lake, semi-deep lake to deep lake. The sediments comprise

r 15m

Mem 3

Mem 2

3 Mem 1

121.8 Ma

Tuchengzi Fm.

Mem 3

Mem 2

Tuchengzi Fm.

121.8 Ma

139.4 Ma

139.4 Ma

125.0 Ma Manchurvchelys liaoxiensis

Lycoplera sinensis Peipiaosteus pan: Anura indcl. Eosipterus yangi Conjuausornis sanclus Con/uciusornis chuonzlious Psillacosaurus sp. Sauropoda mdet. Archae/ruclus liaoningensis

Lycoplera sinensis Peipiuusleus pani Sinamia sp. I.iaohalrailitis graham Callobairachus sanyanensis Mesophryne heipiaoensis Manc hurvchelys liaoxiensis Monjurosuchus sptendens Yaheinosaurtis tenuis Dalinghosaurus ¡ongidigitus Dendrorhynchnides curvidentatus Haopterus gracilis Sinosauropteryx prima Pmiarchaeopteryx robusla Caudipteryx zoui Caudipleryx dongi Beipiaosaurus inexpectus Sinornilhosaurus millenii Psillacosaurus sp. Conjuciusornis sanclus Confiiciusornis suniae Conjuciusornis dui Changchengomis hengdaoziensis Liaoningornis longidilris Eoenantiornis huhleri Zhangheotherium quinquecuspidens Jeholodens jenkinsi

Anura indei.

Psittacosaurus sp. Jeholosaurus shangyuanensis Liaoceratops yamigouensis Incisivosaurus gauihieri Simnenamr changii Re/H'nomamus mhiiKtus Gohiconodon znfiue

16 Stratigraphic sequences of the lower part of the Yixian Formation in Sihetun and the neighboring areas Legends see Fig. 12.

mainly gray, gray-black sandstones, shales and mudstones with rich tuffaceous components. This bed also represents the most important horizon preserving birds and feathered dinosaurs.

Nearly 40 genera and species of vertebrates have been discovered from the Jianshangou Bed, including birds such as Confuciusornis and Liaoningornis, feathered dinosaurs Sinosauropteryx, Beipiaosaurus, Sinornithosaurus, Caudipteryx and Protarchaeopteryx; ornithischian dinosaur Psittacosaurus, pterodactyloids Haopterus and Eosipterus, rhamphorhynchoid pterosaur Dendrorhynchoides\ amphibians Callobatrachus and Mesophryne\ primitive mammals Zhangheotherium and Jeholodens, and fishes Lycoptera sinensis, L.fuxinensis, Peipiaosteus pani.

Among them, Lycoptera sinensis, L.fuxinensis, Peipiaosteus pani, Confuciusornis and feathered dinosaurs are most abundant and notable. The Confuciusornis avian fauna in the Jianshangou Bed represents the earliest known avian fauna in the Jehol Biota. Invertebrates are also abundant in this bed including gastropods, bivalves, conchostracans, ostracods, insects as well as numerous plants (e.g., stoneworts, spores and pollen).

Due to the fragmentary material of Sinornis and Cathayornis (both described in 1992), the most remarkable vertebrate discovery in the Jehol Biota of Liaoning had not been made until 1993 when the earliest beaked bird Confuciusornis sanctus was discovered at the Jianshangou locality in Beipiao City (Fig. 17). The first important mammal fossil from this region, Zhangheotherium quinquecuspidens, a symmetrodon, was also collected at approximately the same time. And the putative angiosperm Archaefructus liaoningensis was found in the neighboring Huangbanjigou locality. In the following years, about 20 new localities such as Sihetun, Zhangjiagou, Heitizigou have been found in the nearby areas, preserving vertebrate-bearing deposits belonging to the Jianshangou Bed of the lower Yixian Formation.

Starting from 1995, the farmers of the Sihetun Village, Beipiao City have also been involved in fossil digging. They have come across some primitive birds near their village. Most of the fossil birds were later recognized as Confuciusornis. The field crew of the IVPP began large-scale excavations at this locality in 1997, and in the four consecutive seasons, we collected hundreds of vertebrate fossils as well as numerous invertebrates and plants. Many findings have drawn worldwide attentions, and the Sihetun locality immediately became the spotlight in paleontological community (Fig. 18). Among the many interesting vertebrates from this locality are primitive birds such as Confuciusornis and Liaoningornis longiditris, feathered dinosaurs such as Sinosauropteryx prima, Beipiaosaurus inexpectus, Sinornithosaurus millenii and the common ornithischian dinosaur Psittacosaurus, pterosaur such as Haopterus gracilis, amphibian Callobatrachus sanyanensis and the primitive mammal Jeholodens jenkinsi. Amazingly, all these fossils are primarily preserved in the shale of about seven meter's thick (Fig. 19).

The colleagues of the Museum of Natural Science (Taiwan) joined the IVPP field crew for the 1999 long field season in the Sihetun area, and collected lots of fishes, dinosaurs, birds, insects and plants. In order to better understand the biostratigraphic framework, we also collected about 150 meters of the core samples from the drillings done at Sihetun, Hengdaozi and Zhangjiagou. Some of the samples are currently under study at the Museum.

The Zhangjiagou locality (Fig. 20) is about three kilometers north of the Sihetun locality, and has produced important feathered dinosaurs such as Caudipteryx zoui, C. dongi and Protarchaeopteryx robusta. We carried out two large-scale excavations in 1998 and 2001, and collected, in addition to the aforementioned taxa, Confuciusornis, Psittacosaurus, turtles and rhamphorhynchoid pterosaur Dendrorhynchoides curvidentatus.

Dawangzhangzi Bed (Member) of the middle Yixian Formation The Dawangzhangzi Bed is best represented by the Fanzhangzi and Shanzui localities in Dawangzhangzi, about 20 km southwest of the town of Lingyuan City (Fig. 21).

The Dawangzhangzi Bed is approximately equivalent to the "Jehol Series" proposed by A. W.

am 17 Jianshangou locality (lower part of Yixian Formation) in Beipiao, Liaoning.

118 Site 1 of Sihetun locality llower part ol' Yixian Formation) in Beipiao. I.iaoning.

119 Close-up view of Site 1. showing IVPP excavation of the year 2000, where a com pi et e Con/uciusornis specimen was discovered during the excursion of the 5"' International meeting of SAPE and the symposium on thejehol Biota.

Jehol Biota Digging
a20 IVPP excavation site of the year 200! at Zhangjiagou locality (lower part of Yixian Formation) in Beipiao, Liaoning.

r cn

■■21 Shanzui site (vicinity) and Fanzhangzi site (beyond) in Dawangzhangzi (middle part of Yixian Formation) of Lingyuan, Chaoyang, Liaoning.
mm 22 Hejiaxin locality (middle part of Yixian Formation) in Totitai, Yixian, Liaonmg.

Grabau (1923). The sediments comprise mainly gray, gray-black sandstones, shales and mudstones with rich tuffaceous components. Fossil-bearing beds comparable to the Dawangzhangzi Bed are the Daxinfangzi Bed in Lingyuan, Dakangpu and Hejiaxin beds in Yixian, Liaoning; and Sichakou and Senjitu beds in Fengning, Hebei. Among the known vertebrate fossils are Lycoptera davidi and L. tokunagai, ascipenseriform Peipiaosteus fengningensis and Protopsephurus liui, turtle Manchurochelys, choristoderes Monjurosuchus and Hyphalosaurus, dinosaurs Sinosauropteryx, Sinornitbosaurus, and Jinzbousaurus, birds Liaoxiornis, Protopteryx and a few Confuciusornis, mammals Sinobaatar and Eomaia, as well as the putative angiosperm Arcbaefructus sinensis. Lycoptera davidi and Hyphalosaurus are most abundant in this bed.

Since 1998, important vertebrate and plant fossils have been discovered from the Dawangzhangzi Bed of the middle Yixian Formation at the Fanzhangzi and Shanzui localities of Lingyuan City. The main fossils from this bed include the juvenile enantiornithine Liaoxiornis delicates, the choristodere reptile Hyphalosaurus lingyuanensis, the multituberculate mammal Sinobaatar lingyuanensis, the earliest known eutherian mammal Eomaia scansoria, the primitive compsognathid Sinosauropteryx and putative angiosperm Arcbaefructus

mm 23 Dongtuyao site. Senjitu (Left) and Jiecaigou site, Sichakou (Right) (middle part of Yixian Formation) in Fengning, Hebei.

sinensis as well as some unpublished materials of feathered theropods, pterodactyloids, Confuciusornis, insects and plants.

Various fossil vertebrates have been also known from the Dawangzhangzi Bed of Yixian Formation at the Hejiaxin, Wangjiagou, and Wanfotang localities, Yixian County, Jinzhou, Liaoning (Fig. 22). They include hundreds ol Hyphalosaurus, the iguanodontid Jinzbousaurus yangi, birds, pterodactyloids and feathered dinosaur Yixianosaurus longimanus.

The primitive birds discovered from the Yixian Formation in the Senjitu-Sichakou Basin, Fengning County, northern Hebei Province (Fig. 23) includeJibeinia luanhera and the most primitive enantiornithine Protopteryx fengningensis. Some very primitive acipenseriform fishes, Protopsephurus liui and Yanosteus longidorsalis, were also found from these localities.

Mi 24 Jingangshan locality (upper part of Yixian Formation) in Yixian, Jinzhou, Liaoning.
Yixian Formation

a25 Field excursion to the Boluochi locality Qiufotang Formation) in Chaoyang, Liaoning, the 5tli International meeting of SAP!" and the symposium on thejeltol Biota [May, 2000).

126 IVPP excavation sites of the year 2000 (Belowl and 2001 (Rightl at Shangheshou locality (Jiufotnng Formation) in Qidaoquanzi, Chaoyang, Liaoning.

Jingangshan Bed (Member) of the upper Yixian Formation The

Jingangshan fossil Bed consists of the lake deposits of the upper Yixian Formation at the Jingangshan locality in Yixian County (Fig. 24). The sediments are mainly gray, gray-black sandstones, shales and mudstones with rich tuffaceous components. The vertebrate assemblage here includes only a few taxa such as Lycoptera muroii, Manchurochelys manchoukuoensis, Yabeinosaurus tenuis, some undescribed pterodactyloid pterosaurs, and birds. Lycoptera muroii is especially abundant in this bed.

Boluochi Bed (Member) of the Jiufotang Formation The Boluochi fossil bed is represented by the deposits at the Boluochi, Dapingfang, Dongdadao, Lianhe and Shangheshou localities in Chaoyang City (Fig. 25). The Boluochi locality is about 50 km west to Chaoyang. The Shangheshou

locality lies in the west suburb of the Chaoyang City. Other localities with comparable fossil-bearing deposits include Meileyingzi and Shengli, Chaoyang; Wujiatun and Xierhuqiao, Yixian. The vertebrate assemblage comprises more than 20 genera and species including Jinanicbthys, Sinopterus dongi, Chaoyangopterus zhangi, Liaoningopterus gui, Microraptor zhaoianus, M. gui, Cathayornis, Chaoyangia, Longipteryx, Yanornis, Yixianornis, Sapeornis and Jeholornis. The Cathayornis avian fauna from this bed represents the second avian fauna of the Jehol Biota.

In 1987, a farmer in Shengli, Chaoyang, Liaoning Province discovered the first fossil bird in the Province, later studied by Paul Sereno and Cheng-gang Rao and named as Sinornis santensis. In 1990, Zhong-he Zhou, then a paleoichthyologist working at the IVPP found several bird specimens from the Lower Cretaceous Jiufotang Formation in the locality of Boluochi, Chaoyang while collecting fishes. Among them was a rather complete bird and was described by Zhou and his colleagues in 1992 as Cathayornis yandica. This was the first bird from the Jehol Biota collected by a professional paleontologist in this region. More than three dozens of bird specimens were unearthed from Boluochi in the following four years by the IVPP field crew.

In 2000, the IVPP team excavated abundant birds, fishes and insects in the Jiufotang Formation at the Shangheshou locality, Chaoyang (Fig. 26). The following year, another even larger-scale excavation there resulted in the discoveries of over a dozen birds, feathered theropods, pterosaurs and turtles as well as abundant fishes. The Shangheshou locality has since become one of the most productive localities of the Jiufotang Formation, much like the Sihetun locality of the Yixian Formation. At the same time, various important vertebrate fossils were also collected in the neighboring areas. Consequently, several new vertebrate taxa have been recognized such as the birds Longipteryx chaoyangensis and Yanornis martini. It is worth noting that the smallest dinosaur Microraptor zhaoianus as well as the infamous specimen "Archaeoraptor" that was composed of the tail of the dinosaur Microraptor zhaoianus and the body of the bird Yanornis martini were also collected from the Jiufotang Formation in these areas.

During the past three years (2001—2003), hundreds of beautifully preserved vertebrate fossils have been collected from the Dapingfang and the neighboring Dongdadao and Lianhe localities, Chaoyang (Fig. 27). These fossils include birds Sapeornis and Jeholornis, pterosaurs Sinopterus, Chaoyangopterus and Liaoningopterus and dromaeosaur Microraptor gui.

At approximately the same time, many important vertebrate fossils were collected from the Wujiatun and Xierhuqiao localities (Fig. 28), also of the Yixian County. They include fishes Protopsephurus, Yanosteus and Sinamia, the ornithurine bird Yixianornis grabaui, the turtle Manchurochelys, the feathered caudipterid as well as pterodactyloids and some other birds.

Despite the extensive paleontological research on the Jehol Biota in the last decade, the precise age of the Biota remains to be an enduring problem as well as an inherited one. Currently, there are three different opinions as regard to the age of the Jehol Biota, i.e., the Late Jurassic, Late Jurassic to Early Cretaceous, and Early Cretaceous. Paleontologists and geologists base their age determination mainly on paleontological and stratigraphic comparisons as well as isotope dating. Recently, using the biostratigraphic work in concert with the dating of the tuff samples in the sediments, most workers have agreed that the whole Jehol Biota belongs to the Early Cretaceous. However, still some workers argue otherwise. For instance, Lo et al. (1999) proposed the Late Jurassic age for the lower part of the Yixian Formation, based on the 40Ar/39Ar dating of the biotite (147 Ma).

In 1995, a joint project by the scientists from both the IVPP and Canada used the laser 40Ar/39 Ar method for the first time to date the major horizons of the Jehol Group. They successfully obtained the age (from volcanic deposits) of the Dawangzhangzi and Jingangshan beds of the Yixian Formation as 122.2 + 0.2-122.5 + 0.3 Ma, and 121.4+ 1.1-121.6+0.4 Ma, respectively. It is noteworthy that in 1993, the age of the basalts overlying the Jiufotang Formation in Inner Mongolia was dated as 110+ 0.52 Ma.

In 1999, paleontologists from the IVPP cooperated with C. C. Swisher III from the Berkeley Geochronology Center on the dating of the Yixian Formation. They dated single crystal sanidine from the tuffs of the sediments, thus obtaining a direct age of the sediments for the first time in the Jianshangou Bed of the Yixian Formation. According to their study, the lower part of the Yixian Formation is 124.6 + 0.2-124.6 + 0.3 Ma. In 2001, Wang et al. (2001) dated with zircon crystal from the tuffs of the same locality using U-Pb method, resulted in an age of 125.2 + 0.9 Ma. These works further confirmed the Early Cretaceous age for the Jehol Biota, and indicated that the Jianshangou Bed that bears Confuciusornis, Zhangheotherium and feathered dinosaurs is about 125 Ma, about 20 Ma younger than the oldest bird Archaeopteryx.

In 2001, Swisher and his Chinese collaborators re-dated new samples using 40Ar/39Ar method, with total fusion and incremental-heating analysis of sanidine and biotites from the tuff samples from the Sihetun locality and the Hengdaozi locality where Lo et al. (1999) collected their biotite samples. The result not only confirmed the 125 Ma age for the Jianshangou Bed, but also indicated the presence of trapped Ar in the biotites, which helped explain why the biotite age was not geologically meaningful. Further, they also dated sanidine from tuff samples from the Tuchengzi Formation, which underlies the Yixian Formation unconformably. The 139.4 Ma age for the upper part of the Tuchengzi Formation lends further credence for the Early Cretaceous age of the Jehol Biota (Fig. 29).

Now, the isotope ages for all the Lujiatun, Jianshangou, Dawangzhangzi, Jingangshan Beds and the Jiufotang Formation are available. The Yixian Formation ranges approximately from Valanginian to Barremian, and the Jiufotang Formation corresponds to the Aptian. Recent vertebrate discoveries have provided further evidence supporting the Early Cretaceous age of the Jehol Biota. Although most workers now have accepted the Early Cretaceous age for the Jehol Biota, more stratigraphie work remains to be done and it will probably be a debatable issue for many years to come.

i m + *

"Ar/mol

£ *

"Ar/%*

*

Ca/K

jf n = 24

Analyses

n= ]<)

] A tm -(125.01 ±0.19 (ISO) ±0.04 (SE)) Ma II «L-TI 1 tm ~ (139 4^

1 WL-St

80 40 0

122 124 126 128 130 132 134 136 138 140 142

Age/Ma no

105 100 95

80 40 0

122 124 126 128 130 132 134 136 138 140 142

Age/Ma

Mil 29 Graphics showing results of a recent isotopic dating on the lower part of the Yixian Formation (125.0 Ma| and the underlying upper part of the Tuchengzi Formation (139.4 Ma) in Beipiao, Liaoning. (See Swisher ill et al., 2002 for details)

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