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Yixian Formation

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Yixian Formation
Type Geological formation
Age Barremian - Aptian
Unit of Jehol Group
Sub-units Jingangshan Bed
Dawangzhangzi Bed
Jianshangou Bed
Lujiatun Bed
Underlies Jiufotang Formation
Overlies Dabeigou Formation?, Tuchengzi Formation
Lithology
Location
Region Liaoning
Country China


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. It is known for its fossils, and is mainly comprised of basalts interspersed with siliciclastic sediments.[1]

HistoryEdit

Japanese occupationEdit

It was initially recognized during the time the Japanese Empire controlled a large chunk of Manchuria (Northern China) called "Jehol". During the occupation of Jehol, many Japanese scientists had noticed fossil remains of extinct fish and reptiles, possibly the champsosaurs. These initial fossil discoveries made by Japanese scientists vanished from history once World War II ended in 1945.

Chinese rediscoveryEdit

By 1949, when administration of the area passed to the Communist Party and its leader Mao Zedong, the fossils of Yixian were studied only by Chinese scientists. It was not until the 1990s when remarkable fossils of birds and dinosaurs were excavated. Since 1996, a number of dinosaur fossils that have revolutionized knowledge of these animals have been found at Yixian; among them are the first known non-avian theropods with feathers. See Jehol Biota.

DatingEdit

For some time, the formation was believed to be from the Late Jurassic-Early Cretaceous boundary, some 145 mya (million years ago). Radiometric dating has since resolved it to be younger; it is now considered to have been deposited in the Barremian to early Aptian, some 125-121 mya.[2]

The Yixian Formation forms the lowest part of the Jehol group, 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.[3] The Yixian Formation is preceded by the older Daohugou Beds, of uncertain Jurassic or Early Cretaceous age, which are sometimes considered part of the Jehol group. The Yixian Formation (including the synonymous Jingangshan, Tuhulu, Jianchang, Lower Volcanic and Volcanic Rock formations) is followed stratigraphically by the slightly younger Jiufotang Formation and the Fuxin Formation.[4] Chiappe et al. argued in 1999 that the oldest beds of the Yixian (those bearing a fauna dominated by confuciusornithid birds) were best separated as a distinct formation, called the Chaomidianzi Formation, with a type locality at the village of Sihetun, approximately 25 km south of Beipiao City.[5] 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.[6]

The Dabeigou Formation in Fengning, Hebei Province may immediately precede the Yixian, or it may be equivalent to the oldest Yixian beds.[1] The Yixian also overlies the Tuchengzi Formation in places.[7]

The Yixian Formation is divided into the following subunits, from most recent to oldest:[1]

PaleoecologyEdit

The Yixian Formation represents the second of three major faunal phases that characterize the Jehol Biota, mainly based on changes in invertebrate diversity. In the Yixian, ostracods (seed shrimp) had diversified considerably, despite a very low diversity in the earlier Dabeigou Formation. Other major invertebrate groups in the Yixian include clam shrimp and insects. Insects, as a group, experienced their largest diversification of the entire Mesozoic era in the Yixian. On the other hand, some invertebrate groups, such as bivalves and gastropods (snails and slugs), were numerous but low in diversity, being mainly represented by one or two dominant species (Arguniella in the case of the bivalves).[1]

Studies of vertebrates have shown support for the division of the Jehol into phases, and the diversity of fish in the Yixian was distinct from older and younger formations, with Lycoptera as the dominant species. The Yixian preserves the first Jehol dinosaurs and pterosaurs (which have not been found in the older Dabeigou Formation), and the first major radiation of birds (only one bird species is known from the Dabeigou). The Yixian also preserves the largest (and only) mammal radiation so far known from the Jehol group. Most vertebrates showed a tendency to climb trees or become arboreal, including many tree-dwelling birds, and climbing mammals and lizards.[1]

Plant life reached its Jehol biota peak in the Yixian. Four species of flowering plant were present (three of Archaeofructus and one of Sinocarpus), as were a variety of horsetails that closely resembled modern species. It is possible that increasing animal and plant diversity were linked. The Yixian is characterized by extensive forests, dominated by trees such as ginkgoes, conifers, cycads, and seed fern trees. Ground cover plants included lycopods, horsetails, ferns, and primitive flowering plants, which were rare compared to the others.[1]

This plant life grew around a series of freshwater lakes, provided with abundant minerals thanks to periodic volcanic eruptions. Volcanic activity, along with periodic wildfires, and noxious gasses released from the lake bottoms caused the ecosystem to be continually destroyed and regrown. This, along with the wide diversity of habitats in the surrounding region, may have contributed to the fast diversification of life forms present in the Yixian ecosystem.[1]

Vertebrate fauna of the Yixian FormationEdit

AmphibiansEdit

Amphibians of the Yixian Formation
Taxa Presence Notes Images

Genus:

  1. Callobatrachus sanyanensis
A frog.

Genus:

  1. Jeholotriton paradoxus
A gilled salamander.

Genus:

  1. Liaobatrachus grabaui
A frog.

Genus:

  1. Liaoxitriton zhongjiani
A salamander related to the earlier L. daohugouensis of the Daohugou Beds.

Genus:

  1. Mesophryne beipiaoensis
A frog with no known living relatives.

Birds and other theropodsEdit

The dinosaurs listed below were compiled in a survey by Xu and Norell in 2006, unless otherwise noted.[8]

Theropod dinosaurs of the Yixian Formation
Taxa Presence Notes Images

Genus:

  1. Archaeorhynchus spathula
  1. An early, advanced short-tailed bird (ornithuran)[9]

Genus:

  1. Beipiaosaurus inexpectus
  1. From the Jianshangou Bed
  1. A therizinosaur

Genus:

  1. Caudipteryx dongi
  2. Caudipteryx zoui
  1. From the Jianshangou Bed
  2. Common, but only over a small region of the Jianshangou Bed
  1. An oviraptorosaur
  2. A second species of Caudipteryx

Genus:

  1. Confuciusornis sanctus
  1. From the Jianshangou Bed, where it is extremely common (several hundred specimens)
  1. A primitive short-tailed bird (pygostylian)

Genus:

  1. Dilong paradoxus
  1. Rare in both the Lujiatun and Jianshangou Beds
  1. A tyrannosauroid

Genus:

  1. Graciliraptor lujiatunensis
  1. Rare in the Lujiatun Bed
  1. A dromaeosaurid

Genus:

  1. Huaxiagnathus orientalis
  1. A compsognathid

Genus:

  1. Incisivosaurus gauthieri
  1. Rare in the Lujiatun Bed
  1. An oviraptorosaur

Genus:

  1. Jinzhouornis yixianensis
  2. Jinzhouornis zhangjiyingia
  1. A pygostylian, possibly a junior synonym of Confuciusornis[10]
  2. Possible synonym of J. yixianensis

Genus:

  1. Liaoningornis longidigitris
  1. An ornithuran[11]

Genus:

  1. Liaoxiornis delicatus
  1. An entantiornithine[12]

Genus:

  1. Mei long
  1. From the Lujiatun Bed
  1. A small troodontid fossilized in a sleeping position

Genus:

  1. Paraprotopteryx gracilis
  1. An enantiornithine[13]

Genus:

  1. Protarchaeopteryx robusta
  1. From the Jianshangou Bed
  1. A possible relative of Incisivosaurus

Genus:

  1. Shenzhousaurus orientalis
  1. From the Lujiatun Bed
  1. A primitive ornithomimosaur

Genus:

  1. Sinocalliopteryx gigas
  1. From the Jianshangou Bed
  1. A large compsognathid.

Genus:

  1. Sinornithosaurus haoiana
  2. Sinornithosaurus millenii
  1. (Placeholder)
  2. From the Jianshangou Bed
  1. A dromaeosaurid, the first ever found with feather impressions
  2. A second species of Sinornithosaurus

Genus:

  1. Sinosauropteryx prima
  1. From the Jianshangou and Dawangzhangzi Bed
  1. The first feathered non-avian dinosaur found, a compsognathid

Genus:

  1. Sinovenator changii
  1. Extremely common in the Lujiatun Beds, where literally hundreds of specimens have been recovered
  1. A troodontid

Genus:

  1. Sinusonasus magnodens
  1. From the Lujiatun Bed
  1. A troodontid

Genus:

  1. Tianyuraptor ostromi
  1. From the Dawangzhangzi Bed
  1. A dromaeosaurid

Genus:

  1. Yixianosaurus longimanus
  1. From the Dawangzhangzi Bed
  1. A basal maniraptoran

Genus:

  1. Zhongornis haoae
  1. A primitive avian with a short but non-pygostylian tail[14]

ChoristoderansEdit

Choristoderans of the Yixian Formation
Taxa Presence Notes Images

Genus:

  1. Hyphalosaurus lingyuanensis

Genus:

  1. Monjurosuchus splendens

FishEdit

Fish of the Yixian Formation
Taxa Presence Notes Images

Genus:

  1. Lycoptera davidi
An osteoglossiform.

Genus:

  1. Mesomyzon mengae
A lamprey

Genus:

  1. Peipiaosteus pani
A fish related to sturgeons

Genus:

  1. Sinamia zdanskyi
A Bowfin

LizardsEdit

Lizards of the Yixian Formation
Taxa Presence Notes Images

Genus:

  1. Dalinghosaurus longidigitus
A lizard

Genus:

  1. Xianglong zhaoi
A gliding lizard

Genus:

  1. Yabeinosaurus tenuis
A lizard related to geckos and skinks

MammalsEdit

The mammals listed below were compiled in a survey by Meng and colleagues in 2006, unless otherwise noted.[15]

Mammals of the Yixian Formation
Taxa Presence Notes Images

Genus:

  1. Akidolestes cifellii
A symmetrodont.

Genus:

  1. Eomaia scansoria
An early placental mammal

Genus:

  1. Gobiconodon zofiae
A triconodont

Genus:

  1. Jeholodens jenkinsi
A triconodont

Genus:

  1. Maotherium sinensis
A symmetrodont

Genus:

  1. Meemannodon lujiatunensis
A multituberculate

Genus:

  1. Repenomamus giganticus
  2. Repenomamus robustus
  1. A tricondodont.
  2. A tricondodont, which ate small dinosaurs

Genus:

  1. Sinobaatar lingyuanensis
A multituberculate

Genus:

  1. Sinodelphys szalayi
A marsupial

Genus:

  1. Yanoconodon allini
A tricondodont

Genus:

  1. Zhangheotherium quinquecuspidens
A symmetrodont

OrnithischiansEdit

The dinosaurs listed below were compiled in a survey by Xu and Norell in 2006, unless otherwise noted.[8]

Ornithischian dinosaurs of the Yixian Formation
Taxa Presence Notes Images

Genus:

  1. Hongshanosaurus houi
A ceratopsian

Genus:

  1. Jeholosaurus shangyuanensis
  1. From the Lujiatun Beds
An ornithopod

Genus:

  1. Jinzhousaurus yangi
  1. From the Dawangzhangzi Beds
An ornithopod

Genus:

  1. Liaoceratops yanzigouensis
  1. From the Lujiatun Beds
A ceratopsian

Genus:

  1. Liaoningosaurus paradoxus
  1. From the Dawangzhangzi Beds
A small ankylosaur

Genus:

  1. Psittacosaurus lujiatunensis
  2. Psittacosaurus major
  3. Psittacosaurus sp.
  • Literally thousands of specimens have been recovered from the Lujiatun Beds. Psittacosaurus is also abundant, although somewhat less common, in the Jianshangou Beds

A ceratopsian

Genus:

  1. Tianyulong confuciusi
A heterodontosaurid

PterosaursEdit

The pterosaurs listed below were compiled in a survey by Wang and Zhou in 2006, unless otherwise noted.[16]

Pterosaurs of the Yixian Formation
Taxa Presence Notes Images

Genus:

  1. Beipiaopterus chenianus
A ctenochasmatid

Genus:

  1. Boreopterus cuiae
A boreopterid

Genus:

  1. Cathayopterus grabaui
A ctenochasmatid

Genus:

  1. Dendrorhynchoides curvidentatus
An anurognathid

Genus:

  1. Eosipterus yangi
A ctenochasmatid

Genus:

  1. Feilongus youngi
A boreopterid

Genus:

  1. Haopterus gracilis
An ornithocheirid

Genus:

  1. Ningchengopterus liuae
A pterodactyloid

SauropodsEdit

Sauropod dinosaurs of the Yixian Formation
Taxa Presence Notes Images

Unranked:

  1. Titanosaur sp.
  1. From the Lujiatun and Jianshangou Beds, fragmentary remains.[8]
  • One or more species of titanosaur has been recovered from the Yixian Formation.

TurtlesEdit

Turtles of the Yixian Formation
Taxa Presence Notes Images

Genus:

Invertebrate fauna of the Yixian FormationEdit

Archaefructus liaoningensis

Fossil of Archaefructus, an extinct genus aquatic plants, found at the Yixian Formation.

Flora of the Yixian FormationEdit

Trace fossils of the Yixian FormationEdit

Trace fossils of the Yixian Formation
Taxa Presence Notes Images

Ichnogenus:

  1. Grallator isp.
  1. From the lower Jianshangou Bed, footprints.
  • Footprints belonging to the Grallator form taxon, belonging to a small theropod. Of known Yixian theropods, the footprints most closely match Caudipteryx.[17]

See also Edit

ReferencesEdit

  1. ^ a b c d e f g Zhou, Z. (2006). "Evolutionary radiation of the Jehol Biota: chronological and ecological perspectives." Geological Journal, 41: 377-393.
  2. ^ Swisher, Carl C., Wang, Yuan-qing, Wang, Xiao-lin, Xu, Xing, Wang, Yuan. (1999). "Creatceous age for the feathered dinosaurs of Liaoning, China". Nature 400:58-61 1 July 1999.
  3. ^ Gu, Z.W. (1983) "On the boundary of non-marine Jurassic and Cretaceous in China" in: "Nanjing Institute of Geology and Paleontology, Academica Sinica" "Stratigraphical Chart in China with Explanatory Text" Science Press, Beijing 1983:65-82.
  4. ^ Sha, Jingeng. (2007) "Cretaceous Stratigraphy of northeast China: non-marine and marine correlation" Cretaceous Research 28(2) pp.146-170April 2007
  5. ^ Chiappe, L.M., Ji, S.A., Ji, Q., and Norell, M.A. (1999). "Anatomy and systematics of the Confuciusornithidae (Aves) from the Mesozoic of North-eastern China." Bulletin of the American Museum of Natural History, 1999.
  6. ^ Chen, P., Q. Wang, H. Zhang, M. Cao, W. Li, S. Wu, and Y. Shen. (2005). "Jianshangou Bed of the Yixian Formation in west Liaoning, China." Science in China Series D - Earth Sciences, 48: 298-312. doi: 10.1360/04yd0038
  7. ^ Wang, Y., Ken, S., Zhang, W. and Zheng, S. (2006). "Biodiversity and palaeoclimate of the Middle Jurassic floras from the Tiaojishan Formation in western Liaoning, China." Progress in Natural Science, 16(1): 222 — 230. DOI: 10.1080/10020070612330087
  8. ^ a b c Xu, X. and Norell, M.A. (2006). "Non-Avian dinosaur fossils from the Lower Cretaceous Jehol Group of western Liaoning, China."Geological Journal, 41: 419-437.
  9. ^ Zhou and Zhang, (2006). "A beaked basal ornithurine bird (Aves, Ornithurae) from the Lower Cretaceous of China." Zoologica Scripta, 35: 363–373.
  10. ^ Hou, L.H., Zhou, Z.H., Zhang, F.C., et al. (2002). "Mesozoic Birds from Western Liaoning." In China Shenyang, China: Liaoning Science and Technology Publishing House
  11. ^ Hou, L.H. (1996). "The discovery of a Jurassic carinate bird in China." Chinese Science Bulletin, 41(2): 1861-1864.
  12. ^ Hou, L.H. and Chen, (1999). "Liaoxiornis delicatus gen. et sp. nov., the smallest Mesozoic bird." Chinese Science Bulletin, 44(9): 834-838.
  13. ^ Zheng, X., Zhang, Z., and Hou, L. (2007). "A new enantiornitine bird with four long rectrices from the Early Cretaceous of northern Hebei, China." Acta Geologica Sinica, 81(5): 703-708.
  14. ^ Gao, C., Chiappe, L.M., Meng, Q., O'Connor, J.K., Wang, X., Cheng, X. and Liu, J. (2008). "A new basal lineage of Early Cretaceous birds from China and its implications on the evolution of the avian tail." Palaeontology, 51(4): 775-791. doi:10.1111/j.1475-4983.2008.00793.x
  15. ^ Meng, J., Hu, Y., Li, C. and Wang, Y. (2006). "The mammal fauna in the Early Cretaceous Jehol Biota: implications for diversity and biology of Mesozoic mammals."Geological Journal, 41: 439-463.
  16. ^ Wang, X. and Zhou, Z. (2006). "Pterosaur assemblages of the Jehol Biota and their implication for the Early Cretaceous pterosaur radiation ."Geological Journal, 41: 405-418.
  17. ^ Xing, L.D., Harris, J.D., Feng, X.Y., and Zhang, Z.J. (2009). "Theropod (Dinosauria: Saurischia) tracks from Lower Cretaceous Yixian Formation at Sihetun Village, Liaoning Province, China and possible track makers." Geological Bulletin of China, 28(6): 705-712.

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