| Popis: |
Two specimens of Metaconularia manni (Roy) from the lower Middle Silurian Scotch Grove Formation (eastern Iowa) exhibit well-defined, relict soft parts replicated in silica. One of these specimens bears phosphatic periderm, while the other specimen is a mold. Present within the erect, undistorted apical region of the specimen preserving periderm, on opposite sides of the peridermal cavity, are two small, elongate masses of silica located near the midlines of two of the four faces. Present in the central portion of the other specimen, at a somewhat greater distance from the apex, are five pairs of hollow, elongate, keeled-pouch-like bodies (pouches), the long axes of which converge on the center of the fossil. Each pair of pouches is associated with a short, narrow, gently curved or broadly u-shaped tube, also composed of silica. Additionally, two of the pouch/tube combinations are associated with a pair of rectilinear furrows that correspond to the paired internal carinae that straddled the conulariid’s facial midlines. We interpret the paired pouches and short tubes in the moldic specimen as relic conulariid soft parts homologous, respectively, to the interradial gonads and retractor muscles of extant, stauromedusan and polypoid scyphozoan cnidarians. Unlike most conulariids, which exhibit four faces, this individual had five faces, an aberrant morphology known in one other conulariid. The two small masses in the other specimen are more difficult to interpret, but they, too, may be relic gonads or longitudinal muscles. These interpretations imply that, as in certain extant scyphozoans, at least one conulariid lost the free-living, sexual medusoid life phase. This file is a rendered CT scan of the silicified "rosette" in UWGM 6834 The 3-D geometry of silicified relic soft parts preserved within the specimens and partially obscured by dolomitic rock matrix was determined using ultra-high resolution (Ketcham and Carlson, 2001), 3-D scanning tomography in the University of Texas High-Resolution X-ray CT Facility (Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin). The CT analysis gathered 625 slices, with a slice thickness and interslice spacing of 0.0554 mm and a field of reconstruction of 26 mm, yielding an interpixel spacing of 0.05078 mm. The resultant 3-D model (Fig. 5) was generated using VGStudioMax. |
