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A New Species of Yunnanozoan with Implications for Deuterostome

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A New Species of Yunnanozoan with Implications for Deuterostome R EPORTS istry, K. S. Birdi, Ed. (CRC Press Inc., Boca Raton, FL, 23. L. H. Sperling, Polymeric Multicomponent Materials (grant EA/TU¨ BA-GEBI˙P/2001-1-1) and the Koc¸ Uni- 1997),࿜࿜࿜࿜ chap. 9. (Wiley-Interscience, New York, 1997), chap. 6. versity Fiat Fund. 18. , G. McHale, M. I. Newton, Langmuir 18, 2636 24. J. Varga, in Polypropylene Structure, Blends and Com- Supporting Online Material (2002). posites, J. Karger-Kocsis, Ed. (Chapman and Hall, Lon- www.sciencemag.org/cgi/content/full/299/5611/1377/ 19. Materials and methods are available as supporting don, 1995), vol. 1, chap. 3. DC1 material on Science Online. 25. We thank A. Altay, M. A. Gu¨lgu¨n of Sabancı Univer- Materials and Methods 20. R. N. Wenzel, Ind. Eng. Chem. 28, 988 (1936). sity, and A. Alkan of Brisa for their help with SEM Figs. S1 and S2 21. A. B. D. Cassie, S. Baxter, Trans. Faraday Soc. 3, 16 (1944). measurements. A.L.D. acknowledges the financial References 22. R. A. Veselovsky, V. N. Kestelman, Adhesion of Poly- support of the Turkish Academy of Sciences in the mers (McGraw-Hill, New York, 2002), chap. 2. framework of the Young Scientist Award Program 11 September 2002; accepted 22 January 2003 and ventral units are rarely touching (Fig. 1, A New Species of Yunnanozoan G and H), suggesting that the entire anterior region could expand and contract in height. with Implications for The expansion would occur by an accommo- dation along the median zone and about an axis of rotation near the posterior of the units. Deuterostome Evolution A skirtlike structure runs around the Degan Shu,1* Simon Conway Morris,2 Z. F. Zhang,1 J. N. Liu,1 entire anterior (Fig. 3, A to J) and is de- Jian Han,1 Ling Chen,1 X. L. Zhang,1 K. Yasui,3 Yong Li4 flected outward and, to some extent, ven- trally (9). The skirt consists of an upper Yunnanozoans are a distinctive clade of Lower Cambrian metazoans. Although barlike unit (Fig. 3, A and B), whereas the widely accepted as deuterostomes, their exact placement within this super- more ventral area is thinner but bears prom- phylum is controversial. Here we describe a new species of Haikouella (H. inent dark lineations (Fig. 3, A, B, and G to jianshanensis) from the Chengjiang Lagersta¨tte (Yunnan, China) with excep- J). The skirt is attached to the anterior ends tional preservation of a number of features. These include external gills, which of the ventral unit (on its mid-area), and the suggest that the origin of the pharyngeal clefts was independent of the gills. upper margin runs around the front end of The diagnostic branchial arches of chordates may, therefore, be composite the dorsal unit to which it may have been structures. No evidence was found for the chordate-like structures that have joined (Fig. 3, A and B). The lower part of been described in other yunnanozoans. We propose that yunnanozoans are the skirt hangs free (Fig. 3, G to J). In this stem-group deuterostomes, allied to the vetulicolians. configuration, the skirt defines a space be- tween itself and the rest of the anterior Yunnanozoans are a distinctive group of more than 1420 specimens of Haikouella body (Fig. 3, A, B, and E to H). metazoans, occurring only in the Chengjiang jianshanensis (520 are well preserved), As in H. lanceolata (4), the gills of H. fossil-Lagersta¨tte located near Kunming, in which predate the other two yunnanozoan jianshanensis consist of six bilaterally sym- southwestern China (1, 2). They are known species (3, 4, 7, 8), we report a number of metrical pairs, with each gill being inclined from the type species Yunnanozoon lividum previously unidentified features. forward from its ventral insertion. In H. jian- (3), Haikouella lanceolata (4), and H. jians- The anatomy of H. jianshanensis differs shanensis, the gills were robust structures, hanensis, a new species described here. The from that of the other two known species in but the cuticle of the individual triangular body plan of yunnanozoans is defined by a the size of the gills. Unlike other yunnano- leaves was thin enough for effective respira- relatively slender anterior bearing metameri- zoans (3, 4, 5–8), in which the dorsal seg- tion (Fig. 2, C and D). At the anterior, they cally arranged gills and an expanded posteri- mented unit is well preserved, this region is have an approximately sigmoidal configura- or section that dorsally bears a prominent only occasionally preserved (Fig. 1, A and tion, but at the posterior, they tend to be more segmented unit with a cuticular covering. B). Possibly, in H. jianshanensis, the cuti- elongate. The gills were attached to the ven- Yunnanozoans have been described as deu- cle was thinner, thereby decreasing the tral unit, just dorsal to circular structures that terostomes but, alternatively, as some sort of preservation potential of the posterior re- may represent the proximal part of the gill or, stem group (5), hemichordates (6), cephalo- gion. The anterior of the main body con- alternatively, pharyngeal openings (Fig. 1, A chordates (7), or craniates (4, 8). These di- sists of two discrete units, dorsal and ven- to F; Fig. 2, A to F; and Fig. 3, K to N). vergences of opinion have arisen on account tral, each in the approximate form of a Observations (4)onH. lanceolata were used of the distinctiveness of the yunnanozoan compressed half cylinder (Fig. 1, G to J). to argue that the dorsal end of each gill was body plan and because postmortem crushing These units are separated by a median zone free and unattached, and in dorsoventrally makes crucial details at the anterior difficult (Fig. 1, A to F and K). The ventral unit is compressed fossils of H. jianshanensis, the to discern (3, 4, 6, 8). Here, on the basis of relatively robust and broadly canoelike, gills also bow outward; however, because of with a straight upper margin and recurved the angle at which such material was buried, 1Early Life Institute and Department of Geology, lower side. The dorsal unit has a more it is not possible to determine the nature of Northwest University, Xi’an 710069, China, and arcuate outline and is generally less well the dorsal termination (Fig. 1, I and J, and School of Earth Sciences and Resources, China Uni- preserved, especially toward its posterior. Fig. 3, I and J). Evidence from laterally pre- 2 versity of Geosciences, Beijing 100083, China. De- The cuticle of the median zone is thin served specimens of H. jianshanensis for a partment of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK. 3Institute and normally decomposed (Fig. 1, A to F, dorsal attachment of the gills includes a con- of Molecular Embryology and Genetics, Division of and Fig. 2, A to F), but occasionally, it sistent alignment with respect to the dorsal Development and Biohistory, Kumamoto University, survives as a smooth membrane (Fig. 2, G unit, and in specimens with an expanded 4 2-2-1 Honjo, Kumamoto 860-0811, Japan. College of and H). The median zone generally decreases median zone, the more widely separated dor- Earth Science and Land Resources, Chang’an Univer- sity, Xi’an 710054, China. in height toward the posterior, which brings sal and ventral units show straighter gills, the dorsal and ventral units into juxtaposition; especially in the anterior region (Fig. 1, A to *To whom correspondence should be addressed. E- mail: [email protected] and [email protected]. however, in different specimens, the overall F; Fig. 2, A to D; and Fig. 3, K to N). Each com.cn width of this region is variable. The dorsal gill has a broad axis with transverse markings 1380 28 FEBRUARY 2003 VOL 299 SCIENCE www.sciencemag.org R EPORTS and is bipectinate, with flattened triangular at intervening levels (Fig. 2, G and H). We (in lateral view) or semicircular (in dorsoven- leaflike structures arising on either side (Fig. interpret this configuration as indicating that tral view) dark area (Fig. 3, C to F). This is 1, E to J; Fig. 2, A to H; and Fig. 3, C to J). the gills were external. probably a cuticular bar. The anterior gut was In laterally preserved specimens, the gills The mouth was housed at the back of the probably relatively voluminous, but in the occupy the highest and lowest films of the recess that is encompassed by the anterior posterior, it extends as a narrow intestine. fossil (10), with the rest of the body situated skirt. The mouth is associated with a recurved This latter region often has a scalloped and Fig. 1. Examples of Haikouella and a reconstruction of H. jianshanensis. Dbv, dorsal blood vessels; Dnc, ?dorsal nerve cord; Ds, dorsal segments; (A, B, and E to J) H. jianshanensis;(C and D) H. lanceolata. All are lateral Du, dorsal unit; Eg, ?epipharyngeal structure; Emz, expanded median views, except for (I) and (J). In (A)and (B), the dorsal posterior segments zone; Es, esophagus; Exg, external gills; G1 to G6, gill arch 1 to 6; L.Cmz, are faintly visible [specimen (226)]. The complete specimen with well- left closed median zone; L.Du, left dorsal unit; L.g1 to L.g6, left gill arch preserved dorsal segments (totaling 10) is shown in (C). A drawing of the 1 to left gill arch 6; Ls, left skirt; M, mouth; R.Cmz, right closed median anterior of (C) is shown in (D). The anterior with an expanded median zone; R.Du, right dorsal unit; R.g1 to R.g6, right gill arch 1 to right gill arch zone [specimen (010)] is shown in (E) and (F), and the anterior with a 6; Rs, right skirt; S, skirt; Sb, bar of skirt; Sbsb, space between skirt and closed median zone [specimen (358)] is shown in (G) and (H).
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