A Basal Middle Cambrian, Echinoderm Rich, Outer Shelf Community in the Kaili Formation (Kaili Biota), Guizhou Province, China

Cambrian echinoderms demonstrate a wide range of morphological variation. In particular, eocrinoids have variable attachment disks, stalks, thecae and feeding structures. In the basal Middle Cambrian Kaili Formation (Kaili Biota), deposited in an outer shelf/upper slope setting, three out of five echinoderm genera are eocrinoids: Sinoeocrinus with small attachment disk, long tapering variably plated stalk, theca with rounded to elliptical sutural pores and depending on ontogenetic stage, 4,5,10 or 15 straight brachioles; Globoeocrinus, with large flattened attachment disk, short fat stalk of small juvenile-like platelets, theca with reduced number of plates, circular, elliptical to triangular sutural pores, and 4,5, or10 long spiral brachioles; Balangicystis with long delicate stalk, no sutural pores and long, possibly branching, brachioles; the forth echinoderm is an undescribed and somewhat rare edrioasteroid; and lastly; a rare new type of blastozoan, probably an eocrinoid offshoot. It has a depressed mitre-like theca composed of polygonal plates with abundant circular to elliptical sutural pores. Probably stalkless but there are several circlets of non-pored plates between the thecal plates and small tessellated attachment disk platelets. Attachment platelets have several circlets of lateral exposure and then fold under the theca to form a skirt-like attachment pad. Attachment probably by some sort of “biogluing”. There is no evidence for ambulacral flooring plates, brachioles attach directly to thecal plates. (Apparently in a manner similar to Lichenoides from the Middle Cambrian of Bohemia). Brachioles are spiraled and up to seven (out of a probable ten) have been observed on a specimen.

All of the echinoderms attach directly to the fine-grained siliciclastic bottom (Bioclastic Index 1 or 2) or to biodetritus (e.g. acotretid brachiopods, trilobite molts). Community structure; diffuse, tiering above seafloor not well defined and most biodetritus not occupied by epibionts. Specimens commonly not current oriented but on some bedding surfaces it is pronounced.