Primary biogenic skeletal structures in Multithecopora (Tabulata, Pennsylvanian) Ismael Coronado a,b, ⁎, Alberto Pérez-Huerta c , Sergio Rodríguez a,b a Departamento de Paleontología, Universidad Complutense de Madrid, C/José Antonio Nováis 2, Ciudad Universitaria, E-28040 Madrid, Spain b Instituto de Geociencias (IGEO. CSIC-UCM), C/José Antonio Nováis 2, Ciudad Universitaria, E-28040 Madrid, Spain c Department of Geological Sciences, University of Alabama, Tuscaloosa, AL 35487, USA abstract article info Article history: Received 6 February 2013 Received in revised form 23 May 2013 Accepted 28 May 2013 Available online 5 June 2013 Keywords: Multithecopora Biomineralization Microstructure Nanocrystal Pennsylvanian and Spain Corals are significant components of fossil marine communities and important for paleoenvironmental recon- structions throughout the Phanerozoic. Despite their abundance and diversity in Paleozoic rocks, the presence, and criteria for the recognition of primary, biogenic skeletal structures is highly controversial. The aim of this study is a multilevel analysis of the diverse morphological elements that form well-preserved specimens of the Carboniferous Multithecopora tabulate coral skeleton. Results indicate that samples are minimally altered by diagenesis, but most importantly that skeletal structures are biogenic in nature, and similar to those of mod- ern and fossil carbonate-producing organisms. Nano- and microcrystals form a complex framework of different domains of crystal morphologies that comprise the bulk of the skeleton in Multithecopora. These domains are thought to be the possible phenotypic response of the genotype of these corals, and had a structural importance during the life of the organism. Overall, this study sheds light for a better understanding on the controversy that exists about the biogenic or abiogenic origin of the Paleozoic coral microstructures. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The ecological significance and diversity of corals (sensu lato) is widely recognized throughout the Phanerozoic. Currently, reef systems worldwide act as archives of global changes, mainly in terms of climate and ocean chemistry, with corals recognized as the principal organisms recording such changes (Corrége, 2006; Cohen et al., 2009; Cantin et al., 2010; Giry et al., 2010; Putron et al., 2010; Martindale et al., 2012; Yu et al., 2012). Simultaneously, studies of both recent and fos- sil corals are, therefore, important to decipher taxonomic and phylo- genetic relationships (e.g., Kato, 1963; Schouppé and Stacul, 1966; Lafuste, 1981a,b, 1983), changes in seawater temperatures and paleotempertures (Corrége, 2006; Cantin et al., 2010; Giry et al., 2010), variations in ocean chemistry (Cohen et al., 2009; Putron et al., 2010; Martindale et al., 2012), and even in radiometric dating of biogenic carbonates (Lazar and Stein, 2011; Yu et al., 2012). In parallel, corals are used as key models for a better understanding of carbonate biomin- eralization (Stolarski, 2003; Dauphin et al., 2008; Cuif et al., 2011; Goffredo et al., 2011). The analysis of fossil corals within the context of these studies re- quires an excellent understanding on whether biomineralized struc- tures are primary or diagenetic products. Recent contributions have demonstrated that the presence of primary skeletal structures can be determined in Cenozoic and Mesozoic taxa (Stolarski and Mazur, 2005; Stolarski et al., 2007), but such determination is highly debated for Paleozoic faunas. Milne-Edwards and Haime (1850), Koch (1882) and Ogilvie (1895) studied the constituents of exoskeletons in Recent scleractinian corals, while Struve (1898) reported important information about microstructures in Paleozoic corals. Kato (1963) and Schouppé and Stacul (1966) defined “fine structures” in Paleozoic corals, which are identifiable by petrographic microscopy, of importance as a taxo- nomic character for fossil corals. Three microstructural basic elements have been recognized in Paleozoic corals: granular, lamellar, and fibrous (Lafuste, 1970; Semenoff-Tian-Chansky, 1974). Based on this information, some authors have used microstructural studies with the purpose of identifying and classifying the evolutionary patterns and morphology of this group and to understand the calcification processes (e.g., Lafuste, 1970, 1978, 1981b, 1983; Lafuste and Plusquellec, 1985; Rodríguez, 1989; Falces, 1997). However, the application of microstructural data as taxonomic criteria in Paleozoic corals has been controversial for more than seventy years (Kato, 1963; Sorauf, 1971, 1978, 1983; Oekentorp, 1984, 2001). Additional studies, using other techniques (e.g. SEM, EPMA, and CL), to check the diagenetic or biogenic origin of microstructures in Paleozoic corals have provided disparate results (Schouppé and Stacul, 1966; Brood, 1978; Mas and Rodríguez, 1990; Brühl and Oekentorp, 1997; Falces, 1997; Webb and Sorauf, 2001, 2002; Fedorowski, 2003). Here, we present a detail microstructural and compositional anal- ysis of well-preserved specimens of the tabulate coral Multithecopora Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 286–299 ⁎ Corresponding author at: Departamento de Paleontología, Universidad Complutense de Madrid, C/José Antonio Nováis 2, Ciudad Universitaria, E-28040 Madrid, Spain. E-mail addresses: ismael.coronado@geo.ucm.es, sergrodr@geo.ucm.es (I. Coronado), aphuerta@as.ua.edu (A. Pérez-Huerta). 0031-0182/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.palaeo.2013.05.030 Contents lists available at SciVerse ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo