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Chen Et Al., Science 2004 Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian Jun-Yuan Chen, et al. Science 305, 218 (2004); DOI: 10.1126/science.1099213 The following resources related to this article are available online at www.sciencemag.org (this information is current as of October 14, 2008 ): Updated information and services, including high-resolution figures, can be found in the online version of this article at: http://www.sciencemag.org/cgi/content/full/305/5681/218 Supporting Online Material can be found at: http://www.sciencemag.org/cgi/content/full/1099213/DC1 A list of selected additional articles on the Science Web sites related to this article can be found at: http://www.sciencemag.org/cgi/content/full/305/5681/218#related-content This article cites 16 articles, 9 of which can be accessed for free: http://www.sciencemag.org/cgi/content/full/305/5681/218#otherarticles on October 14, 2008 This article has been cited by 39 article(s) on the ISI Web of Science. This article has been cited by 15 articles hosted by HighWire Press; see: http://www.sciencemag.org/cgi/content/full/305/5681/218#otherarticles This article appears in the following subject collections: Paleontology http://www.sciencemag.org/cgi/collection/paleo www.sciencemag.org Information about obtaining reprints of this article or about obtaining permission to reproduce this article in whole or in part can be found at: http://www.sciencemag.org/about/permissions.dtl Downloaded from Science (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. Copyright 2004 by the American Association for the Advancement of Science; all rights reserved. The title Science is a registered trademark of AAAS. RESEARCH ARTICLES The fossils discussed here, as well as many additional complex animal forms [e.g., (16)], Small Bilaterian Fossils from derive from a basal black bituminous phos- phorite layer of the lower Weng’an Phospho- 40 to 55 Million Years Before rite Member that was deposited in a shallow marine environment, coincident with a dra- the Cambrian matic swing to a more oxygenated environ- ment (19, 20). Dolostones of the Dengying Jun-Yuan Chen,1,2* David J. Bottjer,3* Paola Oliveri,4 Formation overlie the Doushantuo Formation Stephen Q. Dornbos,3 Feng Gao,4 Seth Ruffins,4 Huimei Chi,5 and contain Cambrian small shelly fossils Chia-Wei Li,6 Eric H. Davidson4 near the top (21). Specimens. Ten specimens were exam- Ten phosphatized specimens of a small (Ͻ180 micrometers) animal displaying ined in this study. The three best preserved clear bilaterian features have been recovered from the Doushantuo Formation, specimens (together with color-coded inter- China, dating from 40 to 55 million years before the Cambrian. Seen in sections, pretation) of Vernanimalcula guizhouena this animal (Vernanimalcula guizhouena gen. et sp. nov.) had paired coeloms gen. et sp. nov. are shown in Fig. 1, and extending the length of the gut; paired external pits that could be sense organs; close-ups of two additional well-preserved bilateral, anterior-posterior organization; a ventrally directed anterior mouth specimens are in Fig. 2. We consider the with thick walled pharynx; and a triploblastic structure. The structural com- specimen reproduced in Fig. 1, A1, the holo- plexity is that of an adult rather than a larval form. These fossils provide the type. Measurements on all studied specimens, first evidence confirming the phylogenetic inference that Bilateria arose well including two that may be a closely related before the Cambrian. species, are in Table 1. The salient features of the fossils follow. The highly elaborated bilaterian animals of and anal openings; localized sense organs; Size. The images considered are inter- on October 14, 2008 the Early Cambrian (1) imply a complex prior and body composed of mesodermal, endoder- preted as roughly coronal sections at different evolutionary process that has, however, re- mal, and ectodermal layers. The LCBA re- levels from the ventral surface of the animal mained enigmatic. The earliest unequivocal quired the genomic apparatus to erect such and at slightly different angles to this surface. bilaterian forms in the fossil record are from complex body plans in the process of de- Given their more or less similar orientation, the Ediacaran biota, e.g., the mollusc-like velopment. Thus, it must have possessed the measurements are comparable: The fos- Kimberella (2). Ediacaran fossils are estimat- the genetic “tool kit” for development silized animal had the shape of a broad oval, ed to extend down to about 20 to 30 million shared by all bilaterians (10), as well as the although in every specimen the external wall years before the Lower Cambrian boundary type of complex gene regulatory program is deformed in one region or another. The (3, 4), which is now dated at 543 (ϩ/–1) that underlies all bilaterian developmental longer axis, i.e., the A-P or oral-anal axis, is million years before the present (5). A recent processes (11). The LCBA was predicted to 124 to 178 ␮m in those examples that are www.sciencemag.org phylogenetic analysis of metazoan protein have been microscopic in dimension and relatively well preserved and of consistent evolution (6) indicates that the last common could well have lacked any very distinctive dimensions in the other specimens as well bilaterian ancestor (LCBA) and the diver- external features (10). (Table 1). The left/right axis averages about gence of the main bilaterian branches oc- Here, we describe microscopic bilaterian 10% less than the long axis in each individual curred between the end of a long period of fossils from the Doushantuo Formation, specimen (about 20% in the related species) intermittent worldwide glaciation about 600 Southwest China, dating from 580 to 600 (Table 1). However, unlike the A-P dimen- million years ago (7–9) and the Cambrian million years ago (4, 12). The fossils derive sion, the width consists partly of coelomic Downloaded from boundary, although this divergence time is from a stratum containing the earliest multi- space and thus is subject to local deforma- more recent than concluded in previous anal- cellular animal forms yet recovered, all mi- tion, as well as expansion due to squashing yses [reviewed in (6)]. The LCBA had to croscopic in scale. Thus far, this assemblage and/or decay processes. The microscopic di- possess sufficient complexity to display the has consisted of adult and embryonic spong- mensions of the original animal were only definitive shared characters of the bilaterians: es, some cnidarian-like forms, and diverse about the size of a modern indirectly devel- bilateral symmetry (more or less); anterior- eggs and embryonic stages that could include oping marine larva, although its multilayered posterior (A-P) body plan organization with some of bilaterian provenance (13–16). anatomical structure is much more complex. dorsoventral specializations; gut with oral The Neoproterozoic Doushantuo Forma- General bilateral A-P organization and tion at Weng’an, Guizhou Province, overlies triploblastic structure. The fossils are bi- 1Nanjing Institute of Geology and Paleontology, Nan- a tillite demarcating perhaps the latest glaci- laterally symmetrical, in respect to their jing 210008, China. 2Laboratory of Pharmaceutical ation in this region (13, 14). The dolostones major features (Fig. 1). The holotype spec- Biotechnology, College of Life Sciences, Nanjing Uni- and phosphorites of the lowermost 30 m rep- imen displays the structure of the animal versity, Nanjing 210093, China. 3Department of Earth resent deposition under anoxic environmental toward its ventral side, with the mouth and Sciences, University of Southern California, Los Ange- conditions (17, 18), within which no animal pharynx at the top of the image (Fig. 1, A1 les, CA 90089, USA. 4Division of Biology 156-29, California Institute of Technology, Pasadena, CA fossil remains have been found, either here or and A2). The mouth opened ventrally. The 91125, USA. 5Department of Biological Science and in contemporaneous strata elsewhere in Chi- second specimen probably represents a Medical Engineering, Southeast University, Nanjing na. These rocks are capped by a karstic ex- more dorsal coronal section, which passes 6 210096, China. Department of Life Science, National posure surface. This unconformity is overlain above the ventrally located mouth and Tsing Hua University, Hsinchu 300, Taiwan, China. by a phosphorite 15 m thick (Weng’an Phos- through the top wall of the pharynx (Fig. 1, *To whom correspondence should be addressed. E- phorite Member) containing phosphoclasts B1 and B2). Both of these sections traverse mail: [email protected] (J.-Y.C.); dbottjer@ usc.edu (D.J.B.) that include very well preserved microfossils. the lumen of the gut, although in the holo- 218 9 JULY 2004 VOL 305 SCIENCE www.sciencemag.org R ESEARCH A RTICLES type some portions of the ventral wall of seen most completely in the specimen in coelomic structures are prominent and ob- the gut are included. The third section (Fig. Fig. 1, B1 and B2. The digestive tract is vious in every one of the 10 specimens 1) displays the lumen of the pharynx (Fig. flanked by paired coeloms, clearly lined included in Table 1. Their topology re- 1, A1 and A2) but apparently tilts ventrally both medially and distally with a heavy quires that the coelomic wall be considered toward the posterior so as to display mainly walled epithelium-like layer of uniform a mesodermal layer (orange in Fig. 1), pe- the lower endodermal wall. The digestive thickness. On each side, the medial and ripheral to the endodermal pharynx and gut tract of this animal extends from the mouth distal walls can be seen to join at both (mauve and tan in Fig.
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