Cole et al.—Camerates from an Upper Ordovician Lagerstätte, Ontario


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Taylor, 1999; Sumrall and Gahn, 2006). The paleoenvironments in which the Bobcaygeon and Verulam formations were deposited have been interpreted as a proximal carbonate shelf that ranged in depth and proximity from shoal to shallow shelf in the Bobcaygeon and from deep shelf to shoal/shallow shelf in the Verulam (Armstrong, 2000). Faunal constituents of the Brechin Lagerstätte have been


reported in the literature from other units in southern Ontario, such as the Kirkfield, Hull, and Cobourg formations, many of which are correlative to the Bobcaygeon and/or Verulam. However, the names for many of these units have changed extensively. Here, we use the most recent and widely accepted nomenclature for these units rather than their historical names. The Bobcaygeon Formation has replaced many units mentioned in older stratigraphic literature, including the Coboconk, Kirkfield, Rockland, Leray, and Hull formations (Liberty, 1969; Uyeno, 1974; Armstrong, 2000; see Swisher et al., 2015). The Kirkfield Formation of earlier workers is equivalent to the middle–upper Bobcaygeon Formation (Liberty, 1967, 1969; Brookfield and Brett, 1988; Brett and Taylor, 1999; Armstrong, 2000). The Cobourg Formation, Ottawa Group (Uyeno, 1974) of earlier workers is equivalent to the lower member of the Lindsay Formation (Liberty, 1967; Williams, 1991; Armstrong and Carter, 2010; Gabdeyan, 2011), which gradationally overlies the Verulam Formation (Brookfield and Brett, 1988; Armstrong, 2000).


Overview of the Brechin Lagerstätte


Figure 1. Locality map: (1) location of study area in southern Ontario, indicated by black box; (2) location of collection sites including the classic Kirkfield Quarry locality (stars) and nearby towns (filled circles) in the Lake Simcoe region.


The Bobcaygeon Formation is stratigraphically older and is overlain by the Verulam Formation. Both formations are part of the middle Simcoe Group, which is equivalent to the Trenton and Ottawa groups (Armstrong, 2000). The Bobcaygeon and Verulam formations are currently considered Late Ordovician (late Sandbian–Katian) in age (Sproat et al., 2015), with the M4-M5 sequence boundary of eastern Laurentia occurring within the Bobcaygeon Formation (Holland and Patzkowsky, 1996). Because the fossiliferous horizons of the Bobcaygeon are largely restricted to the upper member of the formation, the crinoid material described here is Katian in age (Liberty, 1969; Brookfield and Brett, 1988). Both the Bobcaygeon and Verulam formations are com-


prised of bioclastic wackestones, grainstones, and packstones interbedded with calcareous shales and siltstones. The Verulam contains more shale than the underlying Bobcaygeon Formation (Liberty, 1969). Several hardgrounds have been documented in detail from the upper Bobcaygeon and lower Verulam (Brett and Liddell, 1978; Brett and Brookfield, 1984; Brett and Taylor, 1999). These hardground surfaces are commonly heavily burrowed and represent incipient lithification of the sediment that allowed many organisms to encrust the substrate, including edrioasteroids, bryozoans, and holdfasts of crinoids and other pelmatozoans (Brett and Liddell, 1978; Brett and


Previous work.—Crinoids from the Upper Ordovician Trenton Group of Canada were first described by Billings in 1858 and 1859, with preliminary descriptions published in 1856 and 1857. Although the material came from multiple localities, a notable collection was recovered from the vicinity of Kirkfield, Ontario (Fig. 1), but the descriptions of fossil crinoids were cursory. In 1911, Frank Springer produced a more thorough summary of Billings’ Kirkfield collection and documented the taxa recognized from the fauna, but even this treatment was not comprehensive. For example, Springer (1911) listed nine species of camerate crinoids from the Kirkfield collection, but only Reteocrinus alveolatus and Cleiocrinus regius were described or discussed at any length. The remaining seven species recognized were only mentioned in brief comments with regards to their relative degree of commonness or rarity. Since Springer’s (1911) monograph, material from Kirkfield and correlative collections in Ontario has not received a compre- hensive taxonomic treatment. As a result, the fauna is widely recognized by professional and amateur paleontologists alike, yet remains poorly understood from a taxonomic perspective.


Taphonomy.—The crinoid skeleton is composed of numerous, discrete plates that may be weakly cemented, as in the case of camerate crinoids, or uncemented, as in the case of cladids and disparids. In particular, the calyx and arms typically disarticulate quickly after death unless burial and preservation of the specimen occurs rapidly (Brett and Baird, 1986; Brett et al., 1997). Although columnals from the stem are typically robust and may be preserved as isolated elements, it is rare for the entire stem and holdfast to be found in association with the calyx. As a result,


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