347 J. Paleont., 76(2), 2002, pp. 347–376 Copyright  2002, The Paleontological Society 0022-3360/02/0076-347$03.00 MACROSCOPIC CARBONACEOUS COMPRESSIONS IN A TERMINAL PROTEROZOIC SHALE: A SYSTEMATIC REASSESSMENT OF THE MIAOHE BIOTA, SOUTH CHINA SHUHAI XIAO, 1 XUNLAI YUAN, 2 MICHAEL STEINER, 3 AND ANDREW H. KNOLL 1 1 Department of Geology, Tulane University, New Orleans, Louisiana 70118, sxiao@tulane.edu; 2 Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing 210008, P. R. China; 3 Technische Universita ¨t Berlin, Institut fu ¨r Geologie und Pala ¨ontologie, Sekr. ACK 14, Ackerstrasse 71-76, 13355 Berlin, Germany; and 4 Botanical Museum, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138 ABSTRACT—Carbonaceous compression fossils in shales of the uppermost Doushantuo Formation (ca. 555–590 Ma) at Miaohe in the Yangtze Gorges area provide a rare Burgess-Shale-type taphonomic window on terminal Proterozoic biology. More than 100 macrofossil species have been described from Miaohe shales, but in an examination of published and new materials, we recognize only about twenty distinct taxa, including Aggregatosphaera miaoheensis new gen. and sp. Most of these fossils can be interpreted unambiguously as colonial prokaryotes or multicellular algae. Phylogenetically derived coenocytic green algae appear to be present, as do regularly bifurcating thalli comparable to red and brown algae. At least five species have been interpreted as metazoans by previous workers. Of these, Protoconites minor and Calyptrina striata most closely resemble animal remains; either or both could be the organic sheaths of cnidarian scyphopolyps, although an algal origin cannot be ruled out for P. minor. Despite exceptional preservation, the Miaohe assemblage contains no macroscopic fossils that can be interpreted with confidence as bilaterian animals. In combination with other late Neoproterozoic and Early Cambrian body fossils and trace fossils, the Doushantuo assemblage supports the view that body-plan diversification within bilaterian phyla was largely a Cambrian event. INTRODUCTION O UR UNDERSTANDING OF body-plan diversification during the Cambrian Period rests disproportionately on a small number of assemblages exceptionally preserved as carbonaceous com- pressions. The Burgess Shale holds pride of place as the first and most extensively studied of these deposits, but older assemblages such as those at Chengjiang and Sirius Passet indicate that already in the late Early Cambrian, the oceans hosted morphologically complex animals belonging to both stem and crown groups of bilaterian phyla (Conway Morris, 1998a). Trace fossil distribu- tions suggest that at least some of these forms are unlikely to have originated before the beginning of the Cambrian Period. Nonetheless, a Burgess-Shale-type taphonomic window on ter- minal Proterozoic biology would considerably sharpen our un- dertsanding of early body-plan evolution. Burgess Shale-type preservation is defined as ‘‘non-mineraliz- ing organisms preserved as carbonaceous compressions (organic preservation) in fully marine sediments’’ (Butterfield, 1995). Al- though clay mineral replication may play a taphonomic role (Towe, 1996; Orr et al., 1998), the prior entombment of organic matter is key in Burgess Shale-type preservation (Butterfield, 1990, 1995, 1996). Shales in the uppermost part of the terminal Proterozoic Doush- antuo Formation, exposed at Miaohe, Hubei Province, and rough- ly age-equivalent beds of the Lantian Formation at Lantian, Anhui Province (Fig. 1), contain unusually well-preserved carbonaceous compressions. Preserved organisms lived in a (partially restricted) marine environment and show no evidence of biomineralization. Previous study has demonstrated that at least some Miaohe fossils are preserved as coherent organic films that can survive HF mac- eration (Xiao et al., 1998a). Indeed, the carbonaceous nature of the Miaohe assemblage is apparent in almost all macroscopic fos- sils. As such, the Miaohe biota can be considered as a terminal Proterozoic example of Burgess-Shale-type preservation as de- fined by Butterfield (1995). Fossils from Miaohe and Lantian have been described in a number of papers (Zhu and Chen, 1984; Bi et al., 1988; Chen and Xiao, 1991, 1992; Ding et al., 1992, 1996; Chen et al., 1994a, 1994b, 1995; Steiner, 1994; Yuan et al., 1995, 1999; Tang et al., 1997; Xiao et al., 1998a), making it clear that compression fossils are abundant and diverse. Just how diverse, however, remains an open question. Sixty-six generic names and more than 110 spe- cific epithets have been applied by various authors to carbona- ceous macrofossils from Miaohe alone. In addition, Ding et al. (1996) listed more than 180 species of organic-walled microfos- sils from the same locality, including more than two dozen new species without designated type specimens. This paper represents an attempt to clarify the systematic pa- leontology of Miaohe macrofossils, as well as an effort to under- stand their implications for our understanding of the early evo- lution of multicellular organisms. In light of a collaborative re- examination of macrofossils described by Chen and Xiao (1991, 1992), Chen et al. (1994b), Steiner (1994), Yuan et al. (1995); a careful restudy of the Ding et al. (1992, 1996) collection by one of us (XY); and examination of newly collected materials, we recognize only about twenty distinct taxa in the Miaohe biota. Derived lineages of green and, probably, red and brown algae are present in the assemblage, and simple sponge- and cnidarian- grade animals may be, as well. Miaohe fossils, however, display no trace of complex bilaterian body plans found in taphonomi- cally similar Cambrian assemblages. STRATIGRAPHY AND TAPHONOMIC SETTING The South China craton originated by collision between the Yangtze Platform and the Cathaysia Block during the broadly Grenville-age Sibao orogeny (Li et al., 1995). Sedimentary infill- ing of a ca. 750 Ma rift basin is recorded by the lowermost unit of the Sinian System, the Liantuo Formation (Chen et al., 1997). Younger Sinian units accumulated in a passive margin setting. In its type area in the Yangtze Gorges, the younger portion of the Sinian System consists of, in ascending order, the Nantuo tillite, Doushantuo Formation, and Dengying dolomite (Fig. 1). Strati- graphic correlations between the Yangtze Gorges area and more southern regions (e.g., in southern Hunan and Guangxi provinces) have been controversial. For example, it is debatable whether the Banxi Group in the northeast-southwest Sibao orogenic belt is completely pre-Sinian (Chen et al., 1997) or can be correlated with Liantuo sandstones in the Yangtze Gorges area (Liu, 1991). Similarly, it is uncertain how to correlate the Nantuo tillite in the Yangtze Gorges area with the two distinct tillites to the south (Liu,