978


Journal of Paleontology


Figure 7. Examples of Pararotadiscus guizhouensis with associated taxa (indicated by arrows): (1) with Sinoeocrinus lui with holdfast (GTBM-10-10122); (2) with the monoplacophoran Oelandiella cf. O. accordinononta Runnegar and Jell, 1976 (GTB-9-5-2884); (3) with Sinoeocrinus lui with holdfast (GTBM-20-1- 32a); (4) with brachiopods (GTBM-9-3-2a). Scale bar=10 mm.


the bottom. Complete specimens of the diminutive trilobite Pagetia and juvenile individuals of the echinoderms Globoeo- crinus globouensis Zhao et al., 2008 and Kailidiscus chinensis Y.L. Zhao et al., 2010 are associated with P. guizhouensis. They are mainly restricted to the edge and middle ring of the disc (Fig. 5.1–5.4). As with the aforementioned brachiopod specimens, this distribution, together with the planktonic habit of Pagetia (Lu et al., 1963; Zhang et al., 1980), suggests that these species, too, had a commensal relationship with P. guizhouensis. Nota- bly, brachiopods and lobopods associated with eldonioids in the Chengjiang Biota have also been interpreted to represent a similar type of symbiosis (Chen and Zhou, 1997).


Co-Burial.—On the discs of many specimens of P. guizhouen- sis are found a variety of fragmentary and partial fossils. Examples of this material include cranidia and pygidia of trilo- bites, disarticulated brachiopod valves, Wiwaxia sclerites,


echinoderm plates, and algal fragments (Table 1; Fig. 6.1, 6.3– 6.6). Among this material, trilobite debris is the most common, fossil brachiopods valves also are commonly preserved on P. guizhouensis and account for 24% of the 628 specimens. The fragments and individuals of these taxa settled on the carcasses of P. guizhouensis that were lying on the seafloor. The tapho- nomic characteristics of this material are such that they indicate a post-mortem relationship (i.e., taphocoenoses), whereby remains, including carcass of other organisms, became asso- ciated shortly before or during final burial.


Benthic fixation on P. guizhouensis carcasses.—Following death, carcasses of Pararotadiscus guizhouensis sank to the seabed and lay at the sediment-water interface. Many benthic taxa were attracted by of carcass of Pararotadiscus guizhouen- sis. These included eocrinoids with holdfasts, brachiopods with


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