ONTOGENY AND MICROSTRUCTURE OF THE ENIGMATIC CAMBRIAN TOMMOTIID SUNNAGINIA MISSARZHEVSKY, 1969

Abstract: The tommotiids are a significant component of the earliest skeletal animal remains in the fossil record, occurring in large numbers in the Lower Cambrian. Sclerites of the tommotiid genus Sunnaginia have been implicated as integral to hypotheses regarding the evolution of the brachiopod body plan, with a morphology intermediate between the unspecialized sclerites of the tubular Eccentrot-heca and the specialized sclerites of the tannuolinids. Abun-dant Sunnaginia?imbricata sclerites, of a broad ontogenetic spectrum, were recovered from the Comley Limestone, Lower Cambrian (Stages 3–4), Shropshire, UK and compared to Sunnaginia imbricata from the Aldan River, Siberia (uppermost Tommotian). New microstructural data, collected using synchrotron radiation X-ray tomographic microscopy, reveal a unique microstructure for Sunnaginia?imbricat