Evidence for spicule homology in calcareous and siliceous sponges: biminerallic spicules in Lenica sp. from the Early Cambrian of South China JOSEPH P. BOTTING, LUCY A. MUIR, SHUHAI XIAO, XIANGFENG LI AND JIH-PAI LIN Botting, J.P., Muir, L.A., Xiao, S., Li, X. & Lin, J.-P. 2012: Evidence for spicule homology in calcareous and siliceous sponges: biminerallic spicules in Lenica sp. from the Early Cambrian of South China. Lethaia, Vol. 45, pp. 463–475. The relationships of the extant sponge classes, and the nature of the last common ances- tor of all sponges, are currently unclear. Early sponges preserved in the fossil record differ greatly from extant taxa, and therefore information from the fossil record is critical for testing hypotheses of sponge phylogenetic relationships that are based on modern taxa. New specimens of the enigmatic sponge Lenica sp., from the Early Cambrian Hetang Biota of South China, exhibit an unusual spicule structure. Each spicule consists of a sili- ceous core with an axial canal, an organic outer layer and a middle layer interpreted to have been originally calcium carbonate. This finding confirms previous work suggesting the existence of biminerallic spicules in early sponges. Combined with data from other early sponges, the new findings imply that the two fundamental spicule structures of modern sponges were derived from a compound, biminerallic precursor. Spicules are therefore homologous structures in Calcarea and Silicea, and if sponges are paraphyletic with respect to Eumetazoa, then spicules may also have been a primitive feature of Meta- zoa. h Calcarea, Early Cambrian, Hetang Biota, phylogeny, Silicea, taphonomy. Joseph P. Botting [acutipuerilis@yahoo.co.uk], Lucy A. Muir [lucy@asoldasthehills.org] and Jih-Pai Lin [jplin@nigpas.ac.cn; jplin@hotmail.com], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China; Shuhai Xiao [xiao@vt.edu], Depart- ment of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA and State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China; Xiangfeng Li [lxfeng712@163.com], Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China; manuscript received on 16 ⁄ 9 ⁄ 2011; manuscript accepted on 15 ⁄ 12 ⁄ 2011. Sponges (phylum Porifera) are widely thought to be the most primitive of the extant metazoan phyla (e.g. Philippe et al. 2009 and references therein), and as such attract research interest in the hope of elucidat- ing the early history of animals. However, the earliest sponges known from the fossil record are very differ- ent from the majority of extant taxa. Most early sponges, whether hexactinellids, demosponges or the extinct heteractinids or protomonaxonids were thin- walled, globose and solitary. In contrast, most living sponges are morphologically complex, thick walled and clonal. Most sponges have a skeleton of mineralized spic- ules, of either siliceous or calcareous composition (Bergquist 1978). Although their mineralized spicules have a high preservation potential under certain cir- cumstances, the fact that most early sponges did not have their skeletal spicules fused meant that they dis- articulated easily upon death, so complete fossils of non-lithistid sponges are rare. Their fossil record extends back to the Late Precambrian, although most of these reports are ambiguous (Pisera 2006). Sponges became widespread during the ‘Cambrian Explosion’, the interval covering the first appearance and radia- tion of skeletonized animals, although the reasons for the diversification are unclear (reviewed by Marshall 2006). The relationships of the major groups of early sponges (heteractinids, protomonaxonids, tetractinel- lid and ceractinomorph demosponges and various hexactinellids) are still uncertain; despite apparent progress in molecular phylogenetics (e.g. Philippe et al. 2009 and references therein), there is still no consensus on even the basic relationships of the clas- ses. In palaeontology, the recognition of previously unknown complexity in the structure of early spicules (Botting & Butterfield 2005; Bengtson & Vinther 2006), and the presence of a calcarean-like external sheath in hexactinellid spicules (Harvey 2010), sug- gests that the problems stem from unrecognized com- plexity in early sponge evolution. These findings show that features of the structure and composition of the DOI 10.1111/j.1502-3931.2012.00308.x Ó 2012 The Authors, Lethaia Ó 2012 The Lethaia Foundation