Eve of biomineralization: Controls on skeletal mineralogy

The oldest echinoderm faunas from Gondwana show that echinoderm body plan diversification was rapid

“…The calcium carbonate mineralogies utilized by organisms in constructing their skeletons have been shown to reflect fluctuations in the magnesium/calcium ratio of sea water that occurred from late Ediacaran to early Cambrian times [43][44][45][46] . Organisms with a calcium carbonate skeleton apparently utilized the polymorph that was most favourable with respect to ambient seawater conditions at the time, and that, once a clade evolved its skeleton, it usually retained that polymorph type for the remainder of its history 44 .…”

Chronology of early Cambrian biomineralization

“…In the latter two localities, carbonates display δ 13 C oscillations with high positive peaks characteristic of the lower Tommotian boundary beds, although the position of these peaks with respect to this boundary has been questioned (Kouchinsky et al 2001(Kouchinsky et al , 2005(Kouchinsky et al , 2007. The skeleton of archaeocyaths is thought to have been originally mineralized with high-magnesium calcite (Zhuravlev & Wood, 2008). The radiocyaths and cribricyaths are thought to be different groups of aspicular sponges with, respectively, aragonitic and high-magnesium calcitic biomineralization (Zhuravlev & Wood, 2008).…”

“…The skeleton of archaeocyaths is thought to have been originally mineralized with high-magnesium calcite (Zhuravlev & Wood, 2008). The radiocyaths and cribricyaths are thought to be different groups of aspicular sponges with, respectively, aragonitic and high-magnesium calcitic biomineralization (Zhuravlev & Wood, 2008). The radiocyaths first appear in the upper Tommotian of the Siberian Platform , whereas the oldest cribricyaths are known from the Altai-Sayan Folded Area in the first half of the Atdabanian Stage .…”

“…The first articulated calcarean Gravestockia pharetronensis Reitner, 1992 occurs in Australian beds correlated with the Atdabanian Stage (Reitner 1992;Debrenne & Reitner, 2001; online Appendix 1 at http://journals.cambridge.org/geo). According to Zhuravlev & Wood (2008), spicules of first representatives of calcarean sponges are probably highmagnesium calcitic in original composition. Stemgroup sponges, which may combine mineralogy and morphology of calcarean and hexactinellid spicules, are also reported from the Cambrian Series 2 (Botting & Butterfield, 2005;Harvey, 2010; see also Eiffelia Walcott, 1920 in online Appendix 1 at http://journals.cambridge.org/geo).…”

“…Skeletons †Author for correspondence: artem.kouchinsky@nrm.se certainly diversified along with the taxa that obtained them, with 80 % of modern skeletal morphotypes present by the middle Cambrian (Thomas, Sherman & Stewart, 2000). The diversity of minerals employed in early skeletalized animals suggests a limit to the role of ocean geochemistry in the emergence of skeletons, although the primary acquisition of particular skeletal carbonate mineralogies was likely driven by the ocean geochemistry (Zhuravlev, 1993;Bengtson, 1994Bengtson, , 2004Ushatinskaya & Zhuravlev, 1994;Hardie & Stanley, 1997;Stanley & Hardie, 1998;Porter, 2007;Zhuravlev & Wood, 2008;Kiessling, Aberhan & Villier, 2008). Mineralized skeletal parts are only one of many strategies to escape predation, since skeletonized species constitute a minority in modern and ancient marine ecosystems (e.g.…”