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Taphonomy, palaeoecological implications, and colouration of Cambrian gogiid echinoderms from Guizhou Province, China

JIH-PAI LIN^*,, WILLIAM I. AUSICH^*, YUAN-LONG ZHAO and JIN PENG

^* School of Earth Sciences, Ohio State University, Columbus, OH 43210, USA
College of Resource and Environment Engineering, Guizhou University, Guiyang 550003, China
Department of Earth Sciences, Nanjing University, Nanjing, 210093, China

View larger version (17K): [in this window] [in a new window]   Figure 1. Map of China indicating position of Guizhou Province (upper left), and map of Guizhou Province with five important localities for Cambrian echinoderm faunas and the depositional settings during the Cambrian Period (modified from Lin, 2006). Illustrated Kaili gogiids are from Wuliu-Zengjiayan (site 1) and Miaobanpo (site 2) sections. Site 3 is the location of the stratotype of the Kaili Formation, and there is one articulated gogiid reported from this site (Lin et al. 2005). Sites 4 and 5 are lower Cambrian gogiid localities from the Balang Formation (Peng et al. 2005a,b).

View larger version (69K): [in this window] [in a new window]   Figure 2. Illustration of morphological terminology used for Cambrian gogiids from Guizhou Province, China, based on latex casts. See text for details. All scale bars = 5 mm. (a) New early Cambrian species (gogiid sp. 2) with distinctive break in the junction between the theca and holdfast from the Balang Formation, KW-8–229. (b) New early Cambrian species (gogiid sp. 1) with gradational transition between the theca and holdfast from the Balang Formation, ZJ 001. (c) Sinoeocrinus lui from the Kaili Formation, GM-9–5–3701. (d) ‘Sinoeocrinus globus’ from the Kaili Formation, GM-9–4–445. (e) Enlarged view of the holdfast of a S. lui, GTBJ-16–2–26. (f) Enlarged view of the holdfast of a ‘S. globus’, which is a different specimen on the same slab as (d) GM-9–4–445.

View larger version (118K): [in this window] [in a new window]   Figure 3. Specimens of ‘S. globus’ showing different current orientations. Scale bars = 10 mm. (a) Specimen GM-17–298 preserved in non-feeding posture; both brachioles and theca aligned with current direction. (b) Specimen GM-9–3–180 contains two individuals preserved in non-feeding postures; body axes perpendicular to each other. (c) Specimen GM-9–5–1709 contains three individuals preserved in non-feeding posture; body axes oriented in clockwise rotation. (d) Specimen GM-9–2–3530b contains two individuals preserved in a possible feeding posture; body axes pointing opposite to each other.

View larger version (15K): [in this window] [in a new window]   Figure 4. Schematic drawings of entombment patterns exemplified by Guizhou gogiid echinoderms. Types of entombment patterns are explained in Table 1.

View larger version (17K): [in this window] [in a new window]   Figure 5. Schematic drawings of inferred disarticulation of Cambrian stalked echinoderms exemplified by ‘S. globus’, in chronological order. (a) Living position of ‘S. globus’ attached to a skeletal bioclast (indicated by a hyolith). (b) ‘S. globus’ with a few broken brachioles lying on the substrate at death. (c) Relatively simultaneous disarticulation of brachioles, theca and holdfast. (d) Isolated thecal plates, which are the most common gogiid and other eocrinoid elements, preserved in the fossil record, during a late stage of decay.

View larger version (216K): [in this window] [in a new window]   Figure 6. Unusual burial postures and disarticulation patterns of gogiids from the Balang Formation. (a–e) Gogiid indet. sp. 1. (f–j) Gogiid indet. sp. 2. (a) Well-preserved specimen in normal burial position, ZJ-15–5–10. (b) Gogiid specimen in a sunburst pattern, OSU 52612. (c, d) Specimen with mostly articulated plates, selective disarticulation between the basal brachioles and the upper theca, and some disoriented segments of brachioles, OSU 52613. (e) Specimen with mostly articulated plates, partially disarticulated brachioles, and missing the upper middle portion of the theca, OSU 52614. (f) Well-preserved specimen in normal burial position, KW-8–229. (g) Specimen with disarticulated brachioles, partially disarticulated thecal plates scattered around nearby matrix, and a dislocated portion of the holdfast stalk, OSU 52615. (h) Specimen in S-shape posture, OSU 52616. (i) Specimen with partially articulated segments of brachioles and completely disarticulated theca and holdfast (only a few thecal plates remaining), OSU 52617. (j) Two individuals with post-mortem elongation, KMS4–30. Scale bars = 20 mm (a, e); 10 mm (b, f, g); 15 mm (c, d); 5 mm (h, i); 25 mm (j).

View larger version (147K): [in this window] [in a new window]   Figure 7. Evidence of bioturbation, co-occurring trace fossils, and potential trace makers from the Balang Formation. (a, b) Part and counterpart of a slab containing Planolites burrows associated with an articulated gogiid, KMS4–31. (c) An arthropod resting trace Rusophycus, OSU 52618. (d) A trilobite Redlichia (Pteroredlichia) murakamii, KW-12–701. (e) A large bivalved arthropod Tuzoia sp., KW 582. Scale bars = 20 mm (a, b, d, e); 5 mm (c).

View larger version (179K): [in this window] [in a new window]   Figure 8. Exceptionally preserved gogiids with stereom from the Kaili Formation. Scale bars = 5 mm. (a) ‘Sinoeocrinus globus’ (GM-9–4–1524). (b) Sinoeocrinus lui (GM-9–2–3676b). Detailed SEM images are illustrated in Figures 9, 10.

View larger version (167K): [in this window] [in a new window]   Figure 9. ‘Sinoeocrinus globus’ (GM-9–4–1524) with stereomic microstructure from the Kaili Formation. (a) Brachioles. (b) Close-up of a brachiole section. (c) A twisted region of a single brachiole. (d) A portion of thecal plates with stereom in adjacent plates infilled with syntaxial calcite cement. (e) Close-up of thecal plates with stereom. (f) Close-up of brachiolar plates. (g) Close-up of a single thecal plate with stereom. (h, i) Details of stereom in thecal plates. (a, b, g, h) Secondary electron images; (c–f, i) backscatter electron images. Scale bars = 4 mm (a); 400 µm (b); 600 µm (c, f); 1 mm (d, e, g); 100 µm (h, i). Abbreviations: b.s. – brachiolar stereom; c.c. – carbonate cement.

View larger version (191K): [in this window] [in a new window]   Figure 10. Sinoeocrinus lui (GM-9–2–3676b) with stereomic microstructure from the Kaili Formation. (a) Region of the theca with exposed stereom. (b) Close-up of (a) showing a thecal plate with stereom. (c, d) Close-ups of stereom. (e, i) Middle portions of the holdfast revealing stereom around the margins of stalk plates. (f) Close-up of (e) showing the boundary (indicated by the arrow) between the edge of a plate with stereom and the cleavage surface of a plate infilled by syntaxial calcite cement. (g, h) Portions of the lower holdfast with almost all stalk plates preserved with stereom. (j) Close-up of a single, ornamented stalk plate with stereom. (k) Basal portion of holdfast preserved as a natural mould showing the boundary between holdfast stalk and attachment structure (e.g. Fig. 2). (l) Close-up of (k) with a small remnant of stereom. (a, d, e, i, h, l) Backscatter electron images; (b, c, f, g, j, k) secondary electron images. Scale bars = 1 mm (a, e, g, h, i, k); 600 µm (b, f, j); 100 µm (c, d); 300 µm (l). Abbreviations: c.p. – clay-filled plate; c.s. – cleavage surface; h.p. – holdfast plates; p.m. – plate moulds; s.m. – stereomic microstructure.

View larger version (57K): [in this window] [in a new window]   Figure 11. Chemical analyses (indicated by white rectangles) of calcite-bearing gogiid specimens from the Kaili Formation. (a) Thecal plate of ‘S. globus’ (GM-9–4–1524) with stereom. (b) Thecal plate of ‘S. globus’ (GM-9–4–1524) infilled with calcite cement. (c) Stalk plate of S. lui (GM-9–2–3676B) with stereom. (d) Stalk plate of S. lui (GM-9–2–3676B) infilled with calcite cement. (e) Platelets of attachment structure of S. lui (GM-9–2–3676B). (f) Matrix of a S. lui-bearing slab (GM-9–2–3676B). Scale bars = 1 mm (a–d); 600 µm (e, f). See Gaines, Kennedy & Droser (2005, p. 196, fig. 5) or Skinner (2005, p. 169, fig. 1b) for methods.

View larger version (59K): [in this window] [in a new window]   Figure 12. Chemical analyses (indicated either by white rectangles or white arrows) of gogiid specimens from the Balang Formation. All scale bars = 1 mm. (a) Organic carbon concentration in the dark region of a gogiid (OSU 52611) illustrated in Figure 13d. (b) Manganese concentration within a gogiid cavity (OSU 52619). (c) Iron concentration of a gogiid holdfast (OSU 52611). (d) Matrix of a gogiid-bearing slab (OSU 52611). (e) Biotite grain associated with a gogiid-bearing slab (OSU 52611).

View larger version (71K): [in this window] [in a new window]   Figure 13. Gogiids (OSU 52611) with organic preservation of soft parts from the Balang Formation. (a) The entire specimen with nine gogiid individuals (numbered). (b) Close-ups of the group of five individuals, each of which contains a black region in the centre of the theca. A fragment of (b) was analysed under SEM/EDX for chemical composition (see Fig. 12a, c–e). (c) Interpretive drawing of the gogiids (nos 4–8) illustrated in (b) with organic soft-parts (indicated by the dotted polygons). Scale bars = 20 mm (a); 10 mm (b, c).