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Chengjiang Lagerstätte


Abstract

This page provides a brief overview of the Chengjiang Lagerstätte, including geological setting, biota, and significance.

Keywords: Chengjiang, Cambrian, fossil record

Introduction

Lower Cambrian soft-tissue fossils from Chengjiang, near the city of Kunming in Yunnan Province, China, preserve a diverse biota dated approximately 515 to 520 Ma, some 25 Ma after the beginning of the Cambrian and pre-dating the Middle Cambrian Burgess Shale by perhaps 10 to 15 Ma (Martin et al. 2000).

The soft-bodied fossils include diverse algae, medusiform metazoans, chondrophorines, sponges, chancelloriids, ctenophores, cnidarians, nematomorphs, priapulid worms, hyoliths, possible ectoprocts, inarticulate brachiopods, annelid-like animals, anomalocharidids, onychophorans, a wide variety of other arthropods, including trilobites (though few of these), echinoderms, ‘hemichordates’ and probable early chordates, as well as numerous problematical forms that cannot definitely be assigned to well established taxa. They include virtually all the groups known from the Burgess Shale and other Middle Cambrian localities, thus compressing the available time for the morphological diversification of metazoans, known as the Cambrian Explosion, to just 25 Ma or so.

 
 

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The fossils occur in rocks of the Qiongzhusi Formation, cropping out widely in eastern Yunnan Province, South China, where they have been known and studied for some time (e.g. Mansuy 1912, Wand 1941, Lu 1941, Ho 1942) and which include stratotypes for the Southwest China Platform. However, it was not until 1984 when Hou Xianguang collected a surprisingly well preserved specimen of Naraoia from Maotianshan, Chengjiang County (fig. 1), that the exceptional soft-body lagerstätte was recognised.

"The discoveries in 1984 of the Lower Cambrian soft-bodied faunas of Sirius Passet in North Greenland and of Chengjiang in southwest China has had a much greater impact on the significance of the Burgess Shale fauna - it is no longer the sole major source of our knowledge of Cambrian animal life. The older, Sirius Passet fauna includes animals that look significantly more primitive than those in the Burgess Shale,and seems to have few animals, if any, in common. In contrast, the Chengjiang fauna has so many animals in common with the Burgess Shale that it seems to be its geographic extension. This demonstrates that the Cambrian "evolutionary explosion" was over by the time of the Chengjiang fauna. It shows further, that the Burgess Shale/Chengjiang fauna was evolutionarily very stable, and changed little over the 15 to 20 million year interval between the two faunas. Thus the pattern for animal evolution was set in the early and middle Cambrian: short periods of rapid, significant change, exemplified by the Cambrian explosion, alternating with long periods of little change, exemplified by the Burgess Shale/Changjiang fauna" (Collins: Geology and Biology of the Burgess Shale).

ChengjiangLocationMap.jpg (32262 bytes)
Fig. 1: Map showing approximate location of the Chengjiang fossil beds in Yunnan, southern China. The initial discovery was from the vicinity of Lake Fuxiang but now several localities are known from throughout this rather large region.

Geological Setting

Stratigraphy

The Chengjiang fauna derives from the long-known Qiongzhusi Formation (syn. "Chiungchussu") of the Qiongzhusi Stage of the late Early Cambrian (see Brasier 1989, pp. 40-41 for additional reading), located near the western margin of the Southwest China Platform [® sidebar]. The sediments are finely laminated mudstones, formed in an outer shelf detrital belt, in quiet water environments. The frequency of macrobenthos suggests that the water was relatively well oxygenated, although bioturbation is sparse so that possibly only the uppermost layer at the sediment surface was oxygenated.
"The western part of the Platform is different from the eastern part in terms of both sedimentary facies and biofacies. In the former, the Lower Cambrian starts with dolomites and phosphorites, with an abundance of small skeletal fossils, succeeded by detrital rocks bearing a diversity of trace fossils and, ultimately, an abundance of bradoriid arthropods and redlichid trilobites. In the latter, on the other hand, the Lower Cambrian is mainly composed of detrital rocks intercalated with limestone and its fauna is characterized mainly by protolenid and eodiscid trilobites; a few fossils similar to the Chengjiang Lagerstätte have also been found. The Chengjiang fauna probably lived in a tropical sublittoral sea" (Hou et al. 1999, p. 168).
"In eastern Yunnan ... the uppermost part of what is thought to be Precambrian has few if any fossils. Beginning in the earliest Cambrian, shelly elements first appear, then the skin of many unknown types of animals, clearly different from the trilobites and other fossils found in younger rocks. The shelly elements are now known as ‘small shelly fossils.’ The Lower Cambrian biostratigraphy in this area is based mainly on the succession of small shelly fossils at the base of the Lower Cambrian and on the succession of trilobite assemblages in the sequence above. As many as 3 small skeletal fossil biozones (or assemblages) and 11 trilobite biozones are used to divide the Lower Cambrian in this area and elsewhere on the Southwest China Platform. ... The Abadiella Biozone forms the oldest trilobite zone in the Cambrian of China. It is succeeded by the Eoredlichia Biozone, which contains the soft-bodied Chengjiang fauna. The soft-bodied Chengjiang fossils thus occur ... low down in the Lower Cambrian" (Hou et al. 1999, p. 166).

The Chengjiang fauna occurs about 25 m above the earliest trilobites, Parabadiella, found in this area and on the Yangtze Platform. These are most probably coeval with the late Atdabanian trilobites of the Siberian Platform.

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Fig. 2: Stratigraphic column showing key horizons underlying the Chengjiang fauna (after Hou et al. 1999, fig. 36; translation by C. Clowes).

Preservation & Taphonomy

"The preservation of non-mineralized organismal parts probably resulted from repeated rapid burial events that prevented the bodies from destruction by currents, bioturbation and other biotic activities such as by scavengers and carnivores. Burial is also thought responsible for absence of sulphate reduction which apparently was low so that the soft-parts were preserved in a number of different layers in the formation. Well developed anoxic conditions are reflected by several layers with carbon-rich deposits in the Qiongzhusi Formation. These conditions probably led to frequent mass mortalities which may have played a significant role in the soft-part preservation" (International Subcommission on Cambrian Stratigraphy).

Biota

General Characteristics

The Sirius Passet (north east Greenland) fauna is approximately the same age as the Chengjiang fauna, but the two assemblages are not closely similar. Although it is significantly older, the Chengjiang fauna is most easily compared to the Burgess Shale fauna, which does have many families and several genera - though no species - in common. Both Chengjiang and the Burgess Shale are dominated by sponges and arthropods; the two groups together comprising about 60% of each fauna.

"The Chengjiang fauna is basically a benthic fauna. Most species lived directly on the soft, level bottom. A few burrowed in the silty sediment, for instance linguloid brachiopods and presumeably some worms. We can not state for certain that there were any animals that were permanent swimmers, although it is quite clear that many of the arthropods could swim, many of them perhaps very well. At the same time we realize from the mud-filled guts of several arthropods that in many cases their appendages had not yet evolved into the efficient mouthparts they are in modern arthropods. They fed by simply swallowing mud, and this could of course only be done on the bottom. Similar mud-eating habits were common among the hyoliths, a group of extinct animals which had a cone-shaped shell and an operculum to close the open end.
"However, some of the arthropods were carnivores, feeding on small arthropods, worms and the like. Nematomorph and pripulid worms and anomalocaridids were also carnivores, who certainly often swallowed their prey in one piece. If the supposed cnidarians really were cnidarians, they would also have been carnivores. Many small arthropods could have fed from carcasses, for instance the ostracode-like bradoriids. Many animals no doubt strained their food directly from the water. This must have been the case with sponges, brachiopods, eldoniids and echinoderms.
"In summary, we can say that the community is a Burgess Shale-type level-bottom fauna with large proportions of mud-eaters, filter-feeders and carnivores, and with a dominance of arthropods, worms and sponges" (Hou et al. 1999, pp. 169-170).
Perhaps the most surprising aspect of the Chengjiang biota is the wealth of taxa from so many different groups. The fossil assemblages includes diverse algae, medusiform metazoans, chondrophorines, sponges, chancelloriids, ctenophores, cnidarians, nematomorphs, priapulid worms, hyoliths, possible ectoprocts, inarticulate brachiopods, annelid-like animals, anomalocharidids, onychophorans, a wide variety of other arthropods, including trilobites (though few of these), echinoderms, ‘hemichordates’ and probable early chordates, as well as numerous problematical taxa.
It is not only the diversity and early appearance in the fossil record which makes the Chengjiang assemblage fabulous, but also the fine preservation which offers the opportunity to learn more about the morphology of these early creatures. One of the most outstanding examples might be Microdictyon, the isolated sclerites of which were known from numerous localities on various continents, but none of the specialists had any idea how this creature could have been organized. The discovery of these net-like scales of Microdictyon on a worm-like animal resolved the question (see Hou & Ramsköld ????).

Systematics

Phylum Porifera

Class Demospongiae

Sponges are a major component in Lower Cambrian Chengjiang fauna, where they are second only to arthropods in both generic and specific diversity. About 1000 sponge body fossils, distributed among 15 genera and 30 species, have been collected there. The skeletons in most species are represented exclusively by diactins, which form a regular, reticulate skeletal framework. The dermal reticulate organization of spicules is common in the Chengjiang fauna, and these fossils are classified as demosponges. The data from Chengjiang fauna demonstrate that main clade of early sponges, the monaxonid Demospongiae was diverse in the Lower Cambrian. We thus suggest that diactins evolved before other types of spicules. The keratosal demosponges that have skeletons composed entirely of spongin fibers, are seen first in the Lower Cambrian in Chengjiang fauna (Li et al. 1998)

Phylum Arthropoda Siebold & Stannius 1895

Supersubphylum Protarthropoda Lankester 1904

Subphylum Onychophora Grube 1853

Class Xenusia Dzik & Krumbiegel 1989

Order Archonychophora Hou & Bergström 1995

Family Luolishaniidae Hou & Bergström 1995

Genus Luolishania Hou & Chen 1989

Type Species: Luolishania longicruris Hou & Chen 1989

Order Scleronychophora Hou & Bergström 1995

Family Eoconchariidae Hou & Shu 1987

1987 Eoconchariidae Hao & Shu
1988 Eoconchariidae Shu & Chen
1989 Microdictyonidae Chen, Hou & Lu

Genus Microdictyon Bengtson et al. 1981 emend. Chen, Hou & Lu 1989

Species: Microdictyon effusum (type?), M. rhomboidale, M. robisoni, M. sinicum, M. sphaeroides, M. tenuiporatum

Family Hallucigeniidae Conway Morris 1977

Genus Hallucigenia Conway Morris 1977

Type Species: Hallucigenia sparsa Conway Morris 1977

Other Species: Hallucigenia fortis Hou & Bergström 1995

Family Cardiodictyidae Hou & Bergström 1995

Genus Cardiodictyon Hou, Ramsköld & Bergström 1991

Type Species: Cardiodictyon catenulum Hou, Ramsköld & Bergström 1991

Family Onychodictyidae Hou & Bergström 1995

Genus Onychodictyon Hou, Ramsköld & Bergström 1991

Type Species: Onychodictyon ferox Hou, Ramsköld & Bergström 1991

Supersubphylum Euarthropoda Lankester 1904

Subphylum Arachnomorpha Heider 1913

Superclass Trilobitomorpha Størmer 1944

Class Trilobita Walch 1771

Eoredlichia intermedia

Eoredlichia intermedia (25592


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Fig. 2: Eoredlichia intermedia with preserved antennae and mid-gut diverticula (dark blobs in the anterior part of the rhachis). Qiongzhusi Formation, Chengjiang. [Image courtesy of Dr. Gerd Geyer, Institut für Paläontologie, Bayerische Julius-Maximilians-Universität, Würzburg, Germany.]

Subphylum Crustacea

Chuandianella ovata

"In 1912, Charles D. Walcott erected the Family Waptiidae to accommodate Waptia fieldensis, a still poorly understood bivalved arthropod from the Middle Cambrian Burgess Shale of British Columbia, Canada. Several other bivalved arthropods seemingly similar to Waptia have since been discovered, such as the Lower Cambrian taxa Pauloterminus spinodorsalis (nomen nudum) from the Sirius Passet fauna of North Greenland and Chuandianella ovata from the Chengjiang fauna of southwest China.

"Despite their overall waptiid-like appearance, however, each of these animals possesses features which suggest their apparent similarity to Waptia fieldensis may be superficial. Variability in segment number, limb number and limb type between these taxa, for example, suggests these animals may not in fact be closely related.

"Other non-waptiid Cambrian arthropods also possess bivalved carapaces, including the Burgess Shale taxa Canadaspis perfecta and Plenocaris plena. This indicates two alternative evolutionary scenarios. First, the relatively common occurrence of bivalved carapaces may indicate a stem-group clade of bivalved arthropods in the Cambrian, united (at least) by their possession of this specialized carapace. A second, perhaps more likely, possibility is the occurrence of evolutionary convergence, resulting in the presence of a bivalved carapace in multiple unrelated Cambrian arthropod taxa." (Taylor ????)

Phylum Hemichordata

Class, Order, Family Unknown

Genus Yunnanozoon Chen et al.

Refer Shu et al. 1996.

Phylum Chordata

Subphylum Vertebrata

Class Agnatha

sp. names?

"The first fossil chordates are found in deposits from the Cambrian period (545-490 million years ago), but their earliest record is exceptionally sporadic and is often controversial. Accordingly, it has been difficult to construct a coherent phylogenetic synthesis for the basal chordates. Until now, the available soft-bodied remains have consisted almost entirely of cephalochordate-like animals from Burgess Shale-type faunas. Definite examples of agnathan fish do not occur until the Lower Ordovician (475 Myr BP), with a more questionable record extending into the Cambrian. The discovery of two distinct types of agnathan from the Lower Cambrian Chengjiang fossil-Lagerstätte is, therefore, a very significant extension of their range. One form is lamprey-like, whereas the other is closer to the
more primitive hagfish. These finds imply that the first agnathans may have evolved in the earliest Cambrian, with the chordates arising from more primitive deuterostomes in Ediacaran times (latest Neoproterozoic, 555 Ma), if not earlier" (Shu et al. 1999, p. ???).

page an taxa ref?

References

Brasier, M.D. 1989: China and the Palaeotethyan Belt (India, Pakistan, Iran, Kazakhstan, and Mongolia). In Cowie, J.W. and Brasier, M.D. (eds.) The Precambrian-Cambrian Boundary, pp. 40-74. Clarendon Press.

Grotzinger, J.P.; Bowring, Samuel A.; Saylor, Beverly Z.; Kaufman, Alan J. 1995: Biostratigraphic and Geochronologic Constraints on Early Animal Evolution. Science, 270: 598-604.

Hou, Xianguang; Bergström, Jan; Wang, Haifeng; Feng, Xianghong; Chen, Ailin 1999: The Chengjiang Fauna. Exceptionally Well-Preserved Animals from 530 Million Years Ago. Yunnan Science and Technology Press. 170 pp. [In Chinese with English summary.]

Li, Chia-Wei; Chen, Jun-Yuan; Hua, Tzu-En 1998:  Precambrian Sponges with Cellular Structures.  Science 279, issue of 6 February 1998, pp. 879 - 882.

Martin, M.W.; Grazhdankin, D.V.; Bowring, S.A.; Evans, D.A.D.; Fedonkin, M.A.; Kirschvink, J.L. 2000: Age of Neoproterozoic bilaterian body and trace fossils, White Sea, Russia: implications for metazoan evolution.  Science 288: 841-845.

Shu, D-G.; Luo, H-L.; Conway Morris, S.; Zhang, X-L.; Hu, S-X.; Chen, L.; Han, J.; Zhu, M.; Li, Y.; Chen, L-Z. 1999: Lower Cambrian vertebrates from South China. Nature 402: 42-46.

Shu, D.; Zhang, X.; Chen, L. 1996: Reinterpretation of Yunnanozoon as the earliest known hemichordate. Nature 380: 428-430.

Taylor, Rod S. 1999: ‘Waptiid’ Arthropods and the Significance of Bivalved Carapaces in the Lower Cambrian. Palaeontological Association 44th Annual Meeting, University of Edinburgh, 17-20 December 1999 (Oral Presentation)


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