Copyright  2008, SEPM (Society for Sedimentary Geology) 0883-1351/08/0023-0124/$3.00 PALAIOS, 2008, v. 23, p. 124–138 Research Article DOI: 10.2110/palo.2006.p06-089r EVOLUTIONARY HISTORY OF CAMBRIAN SPICULATE SPONGES: IMPLICATIONS FOR THE CAMBRIAN EVOLUTIONARY FAUNA MARCELO G. CARRERA 1 * and JOSEPH P. BOTTING 2 1 Universidad Nacional de Co ´rdoba, CIPAL (Centro de Investigaciones Paleobiolo ´gicas), Facultad de Ciencias Exactas, Fı ´sicas y Naturales, Av. Velez Sarsfield 299 (5000) Co ´rdoba, Argentina; 2 Leeds Museum Discovery Centre, Carlisle Road, Leeds LS10 1LB, UK e-mail: mcarrera@com.uncor.edu ABSTRACT Broad-scale analyses of Cambrian spiculate sponges are scarce. The apparent differences between Cambrian and Ordovician sponge fau- nas were included in Sepkoski’s concept of evolutionary faunas; in these, sponges were regarded as minor contributors to the Paleozoic and modern faunas and insignificant in the Cambrian Evolutionary Fauna. More recent published occurrences of Cambrian and Ordo- vician spiculate sponges and the inclusion of archaeocyaths in the phylum Porifera, however, have altered our understanding of the significance of sponges among Cambrian faunas. The majority of Cambrian occurrences appear to be segregated into two major as- sociations: lower Cambrian sponges in China, and middle Cambrian sponges in North America, primarily British Columbia and Utah. The main associations of spiculate sponges are in siliciclastic deposits from middle-to-deep muddy shelf and basin environments, whereas orchoclad demosponges are associated with shallow carbonate envi- ronments. Four main aspects of sponge biology are considered po- tential factors dictating the distribution of sponges in the Cambrian: their trophic requirements, hydrodynamic constraints, possible bio- geochemical constraints, and the sponge-sediment relationship. A se- ries of critical steps in sponge evolutionary history occurred during the interval from the Proterozoic-Cambrian boundary to the middle– late Ordovician. The lower–middle Cambrian faunas are considered to be a Cambrian evolutionary sponge fauna, with archaeocyaths and diverse monaxonid demosponges as distinctive components. There was a transitional fauna in the upper Cambrian–Lower Ordovician, with orchoclad lithistids dominating shallow environments. Hexacti- nellids began to colonize nearshore siliciclastic settings during this time. The third interval, Middle–Upper Ordovician, corresponds to the Paleozoic Evolutionary Fauna, which is the interval during which lithistids diversified in several suborders and families and the stro- matoporoid and sphinctozoan calcified sponges experienced their first radiation. INTRODUCTION In this paper the main features of early sponge evolution are identified and discussed, particularly the main factors involved in their Cambrian and Ordovician radiation. New ideas and previous interpretations explain- ing the distribution of Cambrian sponges are considered in the light of new database compilations, in an attempt to provide a coherent initial framework for early Paleozoic sponge evolution. Integrated analyses of Cambrian sponges are scarce and restricted mainly to studies of archaeocyath paleogeography and diversification (Zhuravlev, 1986, 2001; Wood et al., 1992; Debrenne and Reitner, 2001). Broad-scope analyses and discussions of Cambrian spiculate sponges are even more limited (Finks 1970; Reitner and Mehl, 1995; Mehl-Janussen, 1999; Carrera, 2005; Botting, 2007), and most are confined to compari- * Corresponding author. sons between the middle Cambrian Burgess Shale Formation and Stephen Formation and to the lower Cambrian Chengjiang faunas (Debrenne and Reitner, 2001; Rigby and Collins, 2004; Dornbos et al., 2005; Steiner et al., 2005; Xiao et al., 2005). Previous attempts to differentiate between Cambrian and Ordovician sponge faunas were integrated at the time of Sepkoski’s proposal of evo- lutionary faunas (Sepkoski, 1981). Sponges were excluded from the Cam- brian Evolutionary Faunas both because archaeocyathan affinities were not clear and because of the scarcity of taxonomic studies on other sponge groups (Sepkoski and Sheehan, 1983). Sponges were also regarded as minor contributors to the Paleozoic and modern faunas. Most spiculate sponges have a very intermittent record owing to the fragility of their skeleton, although they have a continuous history from the Late Neoproterozoic. The record of some groups with coherent or rigid skeletons is good. Isolated spicules are abundant and widely dis- tributed, but faunas of complete nonlithistid sponges are very rare, and the record of sponge diversity is certainly extremely incomplete. Despite this, their record is becoming better known, and database-style compi- lations of published occurrences provide a useful summary of present knowledge, which converges toward reality through time. New published occurrences of Cambrian and Ordovician spiculate sponges have allowed the compilation of an updated database. This new database shows that spiculate and calcified sponges were much more diversified in the Cam- brian than recognized previously. Ordovician occurrences and their dis- tribution patterns were compiled recently by Carrera and Rigby (2004), although this does not include the diverse faunas recently described by Botting (2004, 2005). DATABASE CHARACTERISTICS The majority of Cambrian occurrences are segregated into two major associations (Figs. 1 and 2): lower Cambrian sponges in China (Chen et al., 1989, 1990; Mehl and Reitner, 1993; Rigby and Hou, 1995; Wu et al., 2005; Xiao et al., 2005) and middle Cambrian sponges of North America, notably from British Columbia (Walcott, 1920; Rigby, 1986a; Rigby and Collins, 2004), Utah (Rigby and Gutschick, 1976; Rigby, 1978, 1980, 1983a; Rigby and Church, 1990; Rigby and Gunther, 2003), Vermont and Pennsylvania (Walcott, 1886; Resser and Howell, 1938), Wyoming and Nevada (Howell and van Houten, 1940; Okulitch and Bell, 1955), Texas and Colorado (Wilson, 1950), and Idaho (Church et al., 1999). Lower Cambrian occurrences of sponges in North America are very scarce with only three described species (Rigby, 1987). Other minor associations of Cambrian sponges occur in Australia (Kruse, 1983, 1987; Picket and Jell, 1983; Mehl, 1998), Siberia (Ivantsov et al., 2005), Spain (Sdzuy, 1969; Garcia-Bellido Capdevila, 2003), Germany (Sdzuy, 1969), Argentina (Beresi and Rigby, 1994), Greenland (Rigby, 1986b), Iran (Mostler and Mosleh-Yazdi, 1976; Hamdi et al., 1995), Wales (Salter, 1864), and Ireland (Rushton and Phillips, 1973). Isolated spicules have been recorded elsewhere in the Cambrian (see Zhang and Pratt, 1994; Debrenne and Reitner, 2001), but only those oc- currences of isolated spicules with generic designation are included in