Fossil Lagerstatte Research Articles

EVIDENCE OF PALEOWILDFIRE IN THE EARLY MIDDLE TRIASSIC (EARLY ANISIAN) VOLTZIA SANDSTONE: THE OLDEST POST-PERMIAN MACROSCOPIC EVIDENCE OF WILDFIRE DISCOVERED SO FAR

As direct evidence of paleowildfires, fossil charcoal has so far rarely been reported from Triassic rocks around the world. Indeed there seems to be a scarcity of reports of charcoal between the Permian–Triassic boundary (PTB) and the Ladinian (upper Middle Triassic), an interval of ∼16 myr. There are only a few published records in this time period, consisting either of microscopic charcoal in palynological samples or of indirect evidence such as potential fire scars in wood. Macroscopic charcoal has recently been discovered in the early Middle Triassic (early Anisian) Voltzia Sandstone fossil Lagerstatte in southwestern Germany, providing the oldest macroscopic post-Permian evidence of wildfire currently known. Previous authors have suggested a lack of fuel as a reason for the scarcity of charcoal in Lower-Middle Triassic rocks. As the Voltzia Sandstone includes the oldest known, moderately diverse regional paleoflora after the PTB (interpreted by some authors as representing the recovery of the land flora after end-Permian biotic events), a lack of fuel cannot be claimed as a possible reason for the scarceness of charcoal in these rocks. It seems possible in this particular case that previous researchers simply may have overlooked charcoal remains from this formation, either because they were not recognized or were not considered important at the time.

Biodiversity and taphonomy of the Early Cambrian Guanshan biota, eastern Yunnan

The Guanshan biota from eastern Yunnan (Cambrian Series 2, early Stage 4) is a Burgess Shale-type fossil biota with abundant exceptionally preserved soft-bodied fossils after the discovery of the well-known Cambrian Chengjiang fauna and Kaili biota in South China. The geological settings, sedimentology, taphonomy, and the fossil assemblage of the Guanshan biota are briefly summarized here. The Guanshan biota consists of about 60 taxa belonging to more than 10 metazoan groups and algae, among which the lobopods, eldonids, hyolithids with helens, and green algae are reported for the first time. The common occurrence of soft-bodied preservation in many groups, notably the trilobites and brachiopods, makes the Guanshan biota a significant fossil lagerstatte for understanding the metazoan evolution during Cambrian explosion and taphonomy of the Burgess Shale-type fossils.

Middle Givetian echinoderms from the Schlade Valley (Rhenish Massif, Germany): habitats, taxonomy and ecostratigraphy

Crinoids and ophiocistioids from classical fossil localities of the National Geosite “Schlade Valley”, NE of Bergisch Gladbach (Germany) are reported for the first time. The fossils were derived from the reefal Buchel Formation (lowermost Middle Givetian, Middle Devonian) at the northern flank of the Bergisch Gladbach-Paffrath Syncline (eastern Rhenish Massif). From the abandoned quarry “Im Grubenfeld”, skeletal elements of holothuroids, ophiocistioids and crinoids are documented from a bituminous marly shale horizon in the middle Buchel Formation. The finely bedded shales suffocated an already stressed, muddy “reefal” fauna, which followed on top of a massive Actinostroma stromatoporoid biostrome. The shales characterise an apparently regionally occurring event, herein denominated as “Schlade Event”. It is considered to represent the climax of the transgressive Lower pumilio Event. The autochthonous and vagile epibenthic echinoderm fauna on top of the “Schlade Event Layer” is low diverse. It is regarded, herein, as post disaster fauna, recolonising the dysaerobic softground/soupground together with the well-adapted trilobite Goldius. The cupressocrinitids Halocrinites and Procupressocrinus were recognised from a younger stratum of the upper Buchel Formation within the abandoned “Zimmermann Quarry” near-by. The crinoids settled in high-energy environments of a reef flat in association with characteristic brachiopods (Uncites, Stringocephalus) and bivalves (Eomegalodon) and were swept by storms into reef flat pools. In those exceptional fossil lagerstatten, which are marl-filled obrution deposits, they were parautochthonously preserved together with an autochthonous fauna composed mostly of gastropods and extremely rare allochthonous biota from the open marine realm. Published biozonations of the Buchel Formation, especially on ammonoids, are evaluated, partly corrected and supplemented by ecostratigraphic associations of rugose corals and crinoids. Schlade Event below and Taghanic Event above are major factors controlling biozonation. Taxonomic notes concern revision of the holothuroids from the Schlade Valley and discussion of taxonomic attribution of ophiocistoids and crinoids. All species formerly included in “Abbreviatocrinites” are transferred to genus Halocrinites, which has priority.

Fossil coprolites from the Middle Triassic Luoping Biota and ecological implication

INTRODUCTION Fossilized coprolites provide important insight into diet, physiology and organism interactions such as predator-prey relationships of ancient life. However, preservation of complete coprolites is scarce because most coprolites are fragile and decay or disarticulate soon after release. Here we report a coprolite assemblage from the Anisian-aged Luoping Biota, a fossil Lagerstatte recently discovered from the Middle Triassic in Luoping County, Yunnan Province, SW China (Zhang et al., 2009, 2008). Associated fossils include fishes, marine reptiles, arthropods, bivalves, mollusks, echinoderms, ammonites, lingulid brachiopods, foraminifers, and plants. The preservation and possible producers of these coprolites, and furthermore, the ecological implications are discussed.

Systematics and palaeoecology of Ruminantia (Artiodactyla, Mammalia) from the Miocene of Sandelzhausen (southern Germany, Northern Alpine Foreland Basin)

In more than 20 years of excavation at the fossil lagerstatte Sandelzhausen (Early/Middle Miocene boundary, Burdigalian/Langhian boundary, early middle MN5) a substantial amount of fossil remains of ruminants have been recovered. Currently, it is the largest recorded assemblage of ruminants from the Miocene Northern Alpine Foreland Basin. More than 1,000 teeth, almost 70 antler remains and one skull enable the identification of five ruminants, namely the tragulid Dorcatherium crassum, the palaeomerycid Germanomeryx n. g. fahlbuschi n. sp., and the cervids Lagomeryx parvulus, Lagomeryx pumilio, and Heteroprox eggeri n. sp. Lagomeryx parvulus and L. pumilio have the most extensive record yet known for these species, opening up a much more complete view of them 120 years after the discovery of the type materials. The newly established G. n. g. fahlbuschi n. sp. and H. eggeri n. sp. enlarge our knowledge on the taxonomic composition of Miocene European Ruminantia. Because of the exceptionally large number of specimens, nearly all tooth positions of all five species are documented, thereby completing hitherto partially known character sets. The investigation comprises extensive taxonomic descriptions of all species represented and an interpretation of the palaeoecology based on an analysis of the community structure. This clearly suggests a humid closed canopy forest interspersed with temporary and perennial waters and accompanying open areas. Moreover, a comparison with other, stratigraphically close Molasse Basin communities emphasizes the various peculiarities of the Sandelzhausen community (low species number, cervid-dominance, dominance of L. pumilio over L. parvulus, non-dominance of very small-sized ruminants, comparably high portion of palaeomerycids, all species being browsers, no Eotragus and no Amphimoschus). The investigation also clarifies the similarity with the communities from Undorf and Viehhausen (Germany, MN5). The deduced dynamics in community structure of the late Early and early Middle Miocene Northern Alpine Foreland Basin provides further support for the current hypothesis of a vast wetland environment under the strong influence of alternating dry and flood seasons.

New occurrences of the woodProtocupressinoxylon purbeckensisFrancis: implications for terrestrial biomes in southwestern Europe at the Jurassic/Cretaceous boundary

Abstract: Previously known from the Kimmeridgian–Portlandian of Dorset (UK) only, Protocupressinoxylon purbeckensis wood is reported here from the Kimmeridgian of Asturias (Spain) and Ajoie (Switzerland). The morphospecies taxonomy and nomenclature are discussed, and new supplementary illustrations are given. The P. purbeckensis tree was growing in dry strongly seasonal (tropophilous) environments, and the new occurrences suggest that such a climate prevailed on land all over southwestern Europe at the end of the Jurassic (Kimmeridgian sensu anglico– Portlandian). The review of fossil wood data indicates that such a stressful environment may have constrained terrestrial biocoenoses and their evolution at the Jurassic/Cretaceous boundary. But wood generic diversity curves are also strikingly similar to that drawn 20 years ago for nonmarine tetrapods, implying a fossil Lagerstatte effect.

Deciphering the depositional environment of the laminated Crato fossil beds (Early Cretaceous, Araripe Basin, North-eastern Brazil)

The laminated limestones of the Early Cretaceous Crato Formation of the Araripe Basin (North-eastern Brazil) are world-famous for their exceptionally well-preserved and taxonomically diverse fossil fauna and flora. Whereas the fossil biota has received considerable attention, only a few studies have focused on the sedimentary characteristics and palaeoenvironmental conditions which prevailed during formation of the Crato Fossil Lagerstatte. The Nova Olinda Member represents the lowermost and thickest unit (up to 10 m) of the Crato Formation and is characterized by a pronounced rhythmically bedded, pale to dark lamination. To obtain information on palaeoenvironmental conditions, sample slabs derived from three local stratigraphic sections within the Araripe Basin were studied using high-resolution multiproxy techniques including detailed logging, petrography, μ-XRF scanning and stable isotope geochemistry. Integration of lithological and petrographic evidence indicates that the bulk of the Nova Olinda limestone formed via authigenic precipitation of calcite from within the upper water column, most probably induced and/or mediated by phytoplankton and picoplankton activity. A significant contribution from a benthonic, carbonate-secreting microbial mat community is not supported by these results. Deposition took place under anoxic and, at least during certain episodes, hypersaline bottom water conditions, as evidenced by the virtually undisturbed lamination pattern, the absence of a benthonic fauna and by the occurrence of halite pseudomorphs. Input of allochthonous, catchment-derived siliciclastics to the basin during times of laminite formation was strongly reduced. The δ18O values of authigenic carbonate precipitates (between −7·1 and −5·1‰) point to a 18O-poor meteoric water source and support a continental freshwater setting for the Nova Olinda Member. The δ13C values, which are comparatively rich in 13C (between −0·1 and +1·9‰), are interpreted to reflect reduced throughflow of water in a restricted basin, promoting equilibration with atmospheric CO2, probably in concert with stagnant conditions and low input of soil-derived carbon. Integration of lithological and isotopic evidence indicates a shift from closed to semi-closed conditions towards a more open lake system during the onset of laminite deposition in the Crato Formation.

Giant trilobites and trilobite clusters from the Ordovician of Portugal

Large quarrying surfaces of roofi ng slate in the Arouca Geopark (northern Portugal), formed under oxygen-depleted conditions, have yielded a unique Ordovician fossil lagerstatte that reveals new information on the social behavior of trilobites. It provides several of the world’s largest trilobite specimens (some reaching 70 cm), showing evidence of possible polar gigantism in six different species, as well as numerous examples of monotaxic and polytaxic size-segregated autochthonous trilobite clusters, some of which contain as many as 1000 specimens. These reveal a very diverse social behavior, which includes temporary refuge from predation and synchronous molting and reproduction, demonstrated for the fi rst time in fi contemporary families of three different trilobite orders from a single formation.

Facies and fauna of the Pennsylvanian Buckhorn Asphalt Quarry deposit: a review and new data on an important Palaeozoic fossil Lagerstätte with aragonite preservation

The Pennsylvanian Buckhorn Asphalt Quarry contains the best-preserved Palaeozoic mollusc fauna in the world. Early impregnation of mixed siliciclastic–carbonate rocks (mudstones, pack to grainstones, shell beds, and conglomerates) with hydrocarbons prevented aragonite destruction (“Impregnation Fossil Lagerstatte”). The exceptional preservation comprises shell microstructures, microornaments and early ontogenetic shells. Most gastropods had planktotrophic larval development indicating a high primary production although the remains of phytoplankton are very rare in this and other Late Palaeozoic deposits. Deposition occurred close to a shallow-water coastal area. Mass flow processes (density currents) triggered by storms were involved in the transport mechanisms of some units. Shells of benthic molluscs yield the most diverse known Palaeozoic microboring assemblage, indicating at least partly euphotic conditions. The invertebrate fauna comprises about 160 species and is dominated by molluscs, which is unusual for a Palaeozoic deposit, suggesting that aragonite dissolution produces a major bias in the fossil record. However, most mollusc genera in the Buckhorn deposit are also known from other Pennsylvanian occurrences as recrystallised shells. This shows that preservation bias via preferential aragonite dissolution may be overestimated.

The fossil lagerstätte Sandelzhausen (Miocene; southern Germany): history of investigation, geology, fauna, and age

The Miocene fossil lagerstatte Sandelzhausen in southern Germany ranks among the most important Neogene fossil terrestrial localities in Europe, due to its exceptional record of both macroand microvertebrates as well as invertebrates. From its discovery in 1959 until its final closure in 2001, the site has been the subject of two long-term, systematic digging campaigns (1969–1975 and 1994–2001) as well as occasional collecting by the Ludwig-MaximiliansUniversitat (LMU) together with the Bayerische Staatssammlung fur Palaontologie und Geologie (BSPG; both Munich). In addition to a few plant remains a fossil fauna comprising more than 200 taxa and 50,000 identifiable specimens (Fahlbusch 2003, and this paper Table 1) has been collected including ostracods, molluscs, and, especially, vertebrates of all groups, with an emphasis on mammals (all material housed in BSPG, Munich). Though the vertebrate remains are almost exclusively disarticulated, they represent a variety of both autochthonous and allochthonous environments and they document extensive series of ontogenetic stages and within-species variability. Scientific results derived from Sandelzhausen have been published since 1970 and, ultimately, 26 specialists involved in Sandelzhausen research came together in September 2005 at the Sandelzhausen Symposium in Mainburg to discuss the latest results on all faunistic, ecological, and genetic aspects of the fossil site (Fig. 5a, b; Anonymous 2005, Rossner 2006a, Rossner and Fahlbusch 2006). The present volume resulted from that meeting and presents new contributions to the fossil fauna of Sandelzhausen. The purpose of this paper is to give a short overview and a summary of previous work on the Sandelzhausen fossil site, to document the fieldwork and the geological context, and to discuss the age of the fauna. A German-language summary article including the most recent faunal list, details of the excavation, and the complete publication list up to 2002, including popular accounts (e.g., Fahlbusch and Liebreich 1996), can be found in Fahlbusch (2003). A partly synthetic paper on the genesis and ecology of the site compiling all available research results and new evidence about the fossil lagerstatte will be published elsewhere (in preparation).

Two new species of the side necked turtle genus,Bairdemys (Pleurodira, Podocnemididae), from the Miocene of Venezuela

The side-necked turtle genusBairdemys (Podocnemididae,Shweboemys Group) from the Miocene of Venezuela and Puerto Rico is revised, and four species are diagnosed on the basis of skull characters; two are de-scribed as new.B. hartsteini Gaffney & Wood, 2002, from the Cibao Formation of Puerto Rico, is characterized by a higher skull, with a straight labial ridge and a premaxillary notch;B. venezuelensis (Wood & Diaz de Gamero 1971), from the Urumaco Formation of Venezuela, is characterized by the absence of a premaxillary notch, a high anterior triturating surface convexity, a deep posterior triturating surface concavity, and a short pterygoid mid-line contact;B. sanchezi, new species, from the Urumaco Formation of Venezuela, is characterized by a very low anterior triturating surface convexity and shallow posterior triturating surface concavity, a premaxillary notch, small size, and extensive temporal and cheek emargination;B. winklerae, new species, from the Urumaco Formation of Venezuela, is characterized by an elongate, narrow snout, with a concave labial ridge, and no premaxillary notch. Based on osteological and bone histological results, an additional strongly crushed skull and associated cara-pace fragment of a previously undetermined podocnemidid from the Urumaco Formation of Venezuela can be further referred toPodocnemis or a closely related taxon — again underscoring the importance of this formation as one of the major fossil lagerstatten of turtles in South America.

Facies of two important Early Triassic gastropod lagerstätten: implications for diversity patterns in the aftermath of the end-Permian mass extinction

Two important lagerstatten of Early Triassic gastropods, the Sinbad Limestone (Utah, USA) and the Gastropod Oolite (North Italy) yield about 40% of all described Early Triassic species. This great contribution to the global diversity and the exceptional good preservation render high information content, which characterizes fossil lagerstatten. The Smithian Sinbad Limestone contains the most diverse Early Triassic gastropod fauna. At the type locality, it occurs in single, probably storm-induced shell bed within a series of high energy deposits underlain by intertidal microbial mats and subtidal oolite/peloid shoals. The main shell bed contains about 40 invertebrate taxa. Gastropods, scaphopods, and bivalves are most abundant and form an assemblage, which is dominated by small neritaemorphs, the opisthobranch Cylindrobullina convexa and the scaphopod Plagioglypta (annulated tubes). This assemblage lived on shallow, subtidal soft-bottoms based on sedimentological and ecological characteristics. The Dienerian (to Smithian?) Gastropod Oolite Member (North Italy) has extremely abundant, probably salinity-controlled gastropod faunas with low species richness. Almost monospecific assemblages of Pseudomurchisonia kokeni as well as assemblages with about four species are present in the Gastropod Oolite. Modern hydrobiid mudsnail faunas which are adapted to strongly fluctuating salinity in intertidal to shallow subtidal coastal areas form probably a suitable model for the Gastropod Oolite biota. Gastropods from the Werfen- and Moenkopi-Formation lagerstatten are well preserved compared to other Early Triassic deposits. The high contribution to the global diversity of just two sites suggests very incomplete sampling and preservational bias. However, the low richness of the major faunas reflects depauperate Early Triassic faunas and slow recovery from the Permian/Triassic crisis.

SELDEN, P. & NUDDS, J. 2004. Evolution of Fossil Ecosystems. 160 pp. London: Manson Publishing. Price £39.95 (hard covers), £19.95 (paperback). ISBN 1 84076 040 0; 1 84076 041 9 (pb)

This is primarily a book about fossil lagerstatten, those sites of exceptional preservation where, for one reason or another, the usually savage processes of decay and destruction have been slowed and allowed soft-bodied and poorly mineralized, or otherwise delicate, organisms to enter the fossil record. In ‘normal’ conditions these organisms are guzzled by scavengers and bacteria, and physically destroyed by abrasion. It is well known, therefore, that the fossils found in the vast majority of sedimentary rocks are but a small selection of the organisms that lived in the area at the time of deposition and that this record is massively biased, for example towards those organisms with robust shells, to smaller organisms which are more easily buried, to faunas which inhabited marine rather than terrestrial settings. There is also the realization that many sedimentary units present us with a time-averaged and transported assemblage of organisms which never lived together either in time or space. It is a gloomy outlook for those of us who are interested in palaeoecology. Lagerstatten present us with precious opportunities to see a more complete census of the organisms living at a given time and place. Selden & Nudds have produced a book that introduces the reader to fourteen major lagerstatten from around the world. They are arranged in stratigraphic order. We start logically enough at the celebrated sandstone deposits of the Ediacaran Hills which revealed to …

The earliest-known ancestors of Recent Priapulomorpha from the Early Cambrian Chengjiang Lagerstätte

The taxonomy of an early ancestor of Recent Priapulidae,Xiaoheiqingella peculiaris (=Yunnanpriapulus halteroformis Huang et al., 2004) from the Early Cambrian Chengjiang fossil Lagerstatte, is revised. Morphological characters comprise a pair of caudal appendages rather than a single appendage flanking the trunk end and a possible urogenital duct found inside the preanal region. An additional extremely rare fossil priapulid worm,Paratubiluchus bicaudatus gen. nov., sp. nov. is also described herein. Its diagnostic characters are: an introvert bearing 25 longitudinal rows of scalids, a distinct neck region, no annulus on the oval trunk, and a pair of caudal appendages. The proportion of body parts is similar in size to that of loricate larvae of Recent priapulids and larva-formed Palaeopriapulitidae. Taking account of the features ofXiaoheiqingella, bicaudal appendages are considered to be a synapomorphy of Priapulidae and Tubiluchidae.Paratubiluchus gen. nov. is most likely a candidate for the ancestor of the Tubiluchidae; it probably originated from a larva-formed priapulid with 25 rows of scalids, thus representing an intermediate link between the priapulids in mature-form and the priapulids with lorica.

New Early Cambrian bilaterian embryos and larvae from China

Although knowledge of exceptional Cambrian fossil Lagerstatten has increased dramatically, relatively little information has been uncovered about the early ontogeny of ancient Metazoa. Here we describe new phosphatized eggs and embryos, partly indicating germ band formation, and the earliest known larvae of early bilaterians. Developmental sequences are reconstructed for Pseudooides- and tetramerous-type embryos. Together with these developmental sequences, patterns of germ band formation, irregular radial cleavage types, and unciliated larva with serial divisions and a posterior segment indicate affinities with protostomes, most probably within an ancestral arthropodan lineage.

The missing link in Ginkgo evolution.

The modern maidenhair tree has barely changed since the days of the dinosaurs. The maidenhair tree, or Ginkgo, is a gymnosperm that has been described as a 'living fossil' because it is known to have existed early in the Jurassic period 170 million years (Myr) ago, but a full understanding of its evolution has been impeded by a gap in the fossil record of more than 100 Myr — a crucial period during which the modern ovulate organs evolved from the Jurassic type1. Here we describe a new Ginkgo fossil that was collected from the Lower Cretaceous fossil Lagerstatte (the Yixian Formation2, which is over 121 Myr old3) in China and which fills this gap. This missing link reveals that Ginkgo's reproductive structures at that time were more like those of the present-day Ginkgo biloba than those of the primitive Jurassic type, indicating that their morphology has changed little for over 100 Myr.

The Chengjiang fauna — the oldest preserved animal community

The Chengjiang fauna, an exceptionally well-preserved fossil lagerstatte, from the lower part of the Lower Cambrian Eoredlichia-Wutingaspis Biozone in the Kunming area, Yunnan Province, China is generally introduced, including the research history of the area, stratigraphy in the interval with soft-bodied fossils, geological setting, depositional environment, discovery, distribution, significance and faunal association. The Chengjiang lagerstatte yields various mineralized and nonmineralized skeletons and internal soft parts of organisms, as well as complete soft-bodied animals. The fauna includes virtually all animal phyla that were previously known from the Middle Cambrian and vividly reproduces the appearance of the oldest Phanerozoic animals.

The Burgess Shale arthropod Mollisonia (M. sinica new species): new occurrence from the Middle Cambrian Kaili fauna of southwest China

The Early Cambrian Chengjiang Lagerstätte, Yunnan Province, Southwest China, has become one of the most celebrated Cambrian fossil Lagerstatten not only for perhaps the earliest biota of soft-bodied organisms in the Phanerozoic (Yuan and Zhao, 1999; Zhang et aI., 2001; but see Budd and Jensen, 2000), but also for a number of significant discoveries (Shu et al., 1996a, 1996b, 1999a, 1999b, 2001), proven to be of particular importance for our understanding the Cambrian explosion. Also in Southwest China, Guizhou Province, there is a very significant, although less acclaimed, Middle Cambrian soft-bodied fauna as well, namely the Kaili fauna, which occurs in the Kaili Formation in Kaili area (Kuizhou). The age of the Kaili Formation ranges from late Early to early Middle Cambrian. Regionally, the Kaili Formation is about 222 m thick and consists of three parts. The lowermost part (late Early Cambrian, about 55 m thick) is dominated by thin, calcareous siltstone strata interbedded with limestone layers at the base. The middle part (early Middle Cambrian, ca. 123 m) consists of dark green mudstone and shale, while the uppermost part (ca. 44 m) is composed of interbedded limestone and silty shale. The Kaili fauna is derived from mudstones in the middle part of the formation (Zhao et aI., 1994; Zhu et aI., 2000).

THE BURGESS SHALE ARTHROPOD MOLLISONIA (M. SINICA NEW SPECIES): NEW OCCURRENCE FROM THE MIDDLE CAMBRIAN KAILI FAUNA OF SOUTHWEST CHINA

The Early Cambrian Chengjiang Lagerstätte, Yunnan Province, Southwest China, has become one of the most celebrated Cambrian fossil Lagerstatten not only for perhaps the earliest biota of soft-bodied organisms in the Phanerozoic (Yuan and Zhao, 1999; Zhang et aI., 2001; but see Budd and Jensen, 2000), but also for a number of significant discoveries (Shu et al., 1996a, 1996b, 1999a, 1999b, 2001), proven to be of particular importance for our understanding the Cambrian explosion. Also in Southwest China, Guizhou Province, there is a very significant, although less acclaimed, Middle Cambrian soft-bodied fauna as well, namely the Kaili fauna, which occurs in the Kaili Formation in Kaili area (Kuizhou). The age of the Kaili Formation ranges from late Early to early Middle Cambrian. Regionally, the Kaili Formation is about 222 m thick and consists of three parts. The lowermost part (late Early Cambrian, about 55 m thick) is dominated by thin, calcareous siltstone strata interbedded with limestone layers at the base. The middle part (early Middle Cambrian, ca. 123 m) consists of dark green mudstone and shale, while the uppermost part (ca. 44 m) is composed of interbedded limestone and silty shale. The Kaili fauna is derived from mudstones in the middle part of the formation (Zhao et aI., 1994; Zhu et aI., 2000).

Reinterpretation of Yunnanozoon as the earliest known hemichordate

THE Chengjiang fossil Lagerstatte is one of the earliest and most important palaeontological sites from the Phanerozoic era1,2, about 530 million years ago3. It yields extremely abundant and remarkably preserved soft-bodied fossils and shells with soft parts of various kinds, including bradoriids4–6, trilobites7,8, crustaceans9, brachiopods, worms, sponges, algae and many unknown forms10–13. One of these fossils is Yunnanozoon14, which we reinterpret here as the earliest known hemichordate. Possessing half of the characteristic chordate features and providing an anatomical link between invertebrates and chordates15, Hemichor-data is a minor but important phylum in evolutionary biology. Hemichordates comprise two main groups: the enteropneusts, or 'acorn worms', and the pterobranchs. Apart from the presumable inclusion of graptolites in pterobranchs16–19, there are very few hemichordate fossils2,17,20. Although Yunnanozoon is superficially similar to the chordates21, its typical tripartite body plan is broadly consistent with that of living balanoglossid hemichor-dates (enteropneusts).