 2002 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org. Geology; April 2002; v. 30; no. 4; p. 363–366; 4 figures. 363 Towering sponges in an Early Cambrian Lagersta ¨tte: Disparity between nonbilaterian and bilaterian epifaunal tierers at the Neoproterozoic-Cambrian transition Xunlai Yuan Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing 210008, China Shuhai Xiao* Ronald L. Parsley    Department of Geology, Tulane University, New Orleans, Louisiana 70118, USA Chuanming Zhou Zhe Chen Jie Hu    Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing 210008, China Figure 1. Generalized stratigraphy of Hetang For- mation. 1: Lower Cambrian stages of Siberia. 2: Recently proposed Cambrian series and stages of south China (Peng and Babcock, 2001). 3: Tradi- tional Lower Cambrian stages of south China. Cor- relations between south China and Siberia are ap- proximate. Sponge fossils reported in this paper are from lower Hetang Formation. ND—Nemakit- Daldynian, JN—Jinningian, LGW—Leigongwu till- ite, SSF—small shelley fossil. ABSTRACT Epifaunal, suspension-feeding bilaterian animals in the Cam- brian lived close to the sediment-water interface, and hence their ecological tiering levels were low (10 cm). Here we report an Early Cambrian (Diandongian or probably Tommotian-Atdaban- ian) Lagersta ¨tte from the Hetang Formation in Anhui Province, south China. The Hetang biota is characterized by high-tiering (to 50 cm) sponges and small (0.5 cm) bilaterians (including ortho- thecid hyoliths and bivalved arthropods). Nonbilaterian suspension feeders (sponges, cnidarians, and archaeocyathids) as high-tiering animals and bilaterian suspension feeders as low-tiering animals also characterize other Neoproterozoic-Cambrian assemblages, such as the Ediacaran, Chengjiang, Burgess Shale, and Sinsk bi- otas. These data are consistent with medium- to high-tiering levels in Neoproterozoic-Cambrian epifaunal communities, but suggest that nonbilaterians achieved such tiering levels long before bila- terian suspension feeders did so in the Early Ordovician. The dis- parity between bilaterian and nonbilaterian tierers during the Neo- proterozoic-Cambrian transition and the delayed appearance of high-tiering bilaterians demand phylogenetic and ecological expla- nations. The Cambrian substrate revolution may have triggered a cascade of ecological evolution, including the rise of bilaterian an- imals in high-tiering levels during the Ordovician radiation of the Paleozoic fauna. Keywords: Early Cambrian, south China, Hetang Formation, sponges, epifaunal tiering. INTRODUCTION Phylogenetic radiation and ecological expansion of metazoans are two equally important aspects of the Cambrian radiation (Zhuravlev and Riding, 2001). However, reconstruction of metazoan diversity and ecological complexity during the initial period of the Cambrian radi- ation does not achieve the same level of accuracy as in later Phaner- ozoic time. This is because the Lower Cambrian (particularly the Dian- dongian Series of south China and the Nemakit-Daldynian stages in Siberia; Peng and Babcock, 2001) is characterized by small shelly fos- sils (Qian and Bengtson, 1989), most of which are disarticulated spic- ules and sclerites. As such, the search for articulated fossils and Bur- gess Shale–type biotas in the Lower Cambrian continues to be an important step toward a better understanding of the biology and ecol- ogy of Early Cambrian marine communities. Here we report an Early Cambrian (Diandongian; probably Tommotian-Atdabanian equivalent) Lagersta ¨tte characterized by large articulated sponges and small bila- terian animals. Together with other Neoproterozoic and Early Cambrian *E-mail: sxiao@tulane.edu. metazoan fossils, these fossils suggest that tiering heights of decimeters or greater have been attained in the Neoproterozoic–Early Cambrian (Ausich and Bottjer, 2001), but only by suspension-feeding nonbila- terians. The distinction between bilaterians versus nonbilaterians in tiering analysis allows us to seek phylogenetic and ecological expla- nations for the late appearance of high-tiering bilaterians. GEOLOGIC SETTING AND AGE CONSTRAINTS The sponge fossils are from Lower Cambrian black shales of the Hetang Formation near Xiuning (29°55'N, 118°05'E) in Anhui Prov-