Taxonomy, taphonomy, and ecology of Silurian (late Telychian) conulariids from the Waukesha Lagerstatte, Wisconsin
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The Silurian (late Telychian Stage) Brandon Bridge Formation, Wisconsin, USA, hosts a diverse biota including arthropods, annelids, graptolites, brachiopods, corals, sponges, and algae, some of which exhibit exceptional soft-bodied preservation. Whilst many of the rarer, enigmatic constituents of the Waukesha Konservat-Lagerstatte have received taxonomic and taphonomic study, some of the more common species remain poorly documented. In order to provide a more complete account of the ecology and diversity of the assemblage, this study is focused on the description of a prolific Waukesha faunal element--the conulariids. The aims of the thesis are three-fold. Firstly, we provide a systematic description of the two conulariid species known from the Waukesha Lagerstatte. Secondly, we assess the general taphonomy and preservational pathways of the conulariids. Thirdly, we investigate the identity of, and paleoecological relationship between the conulariids and their epibionts. Specimens (n = 40) borrowed from the University of Wisconsin Geology Museum, Madison, USA were examined using a combination of light microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy (SEM-EDS), to assist in the classification of these taxa. There are two distinct species from this assemblage: Conularia niagarensis Hall, 1852 and Metaconularia cf. manni (Roy, 1935). EDS data shows that the conulariid test is composed of secondary francolite (calcium phosphate); we infer that these originally biomineralized organisms were exposed to post-burial demineralization from shifting pH conditions, resulting in their uncommon two-dimensional preservation, before later taphonomic or diagenetic replacement via francolite. Holdfast scars present on the conulariid test offer a unique glimpse into the paleoecology of this Silurian benthic assemblage. The holdfast morphology bears a close resemblance to that of the epibiont Sphenothallus which is also present in the Waukesha Biota. Statistical analysis of holdfast size and distribution on the conulariid test gives insight to the nature of their symbiotic relationship. Our results did not find any significant support for a parasitic relationship. However, commensalism cannot be ruled out and serves as an alternative explanation for the relationship between these two organisms.