Chengjiang Fauna: Marine animals from 530 million years ago

Author: Hou Xiangguang / Country: Mainland China
Publisher:
Publish Date: 1999-05-01
Features: [Excerpt:] The animal body is relatively large with a circular outline, with adult individuals reaching diameters of over 100 mm. The back has about 80 radial canals, and the abdomen has about 40 radial canals, all extending from the central cavity to the edge. The U-shaped digestive tract is wide and clear, surrounding the center to the edge of the animal body by about half the distance, partially appearing black and sometimes filled with mud. This fossil is one of the most abundant species in the Chengjiang fauna and is well-preserved, often found in clusters. It was initially described as a jellyfish fossil belonging to the Cnidaria phylum (Sun Weiguo et al., 1987). Later, British paleontologist Conway Morris visited Nanjing to examine these specimens and concluded that both Craspedostoma and Yunnanmedusa are late synonyms of Eldonia (see Conway Morris and Robison, 1988). Eldonia was originally discovered in the Burgess Shale of Canada and later found in Utah, USA. It has a nearly century-long research history, but its taxonomic position remains unclear. Initially, Walcott (1911) classified it as a sea cucumber in the Echinodermata phylum, and both supporters and opponents of this classification emerged. Durham (1974) wrote a dedicated article reviewing the research history of this animal, concluding it was an echinoderm. Paul and Smith (1984) expressed doubts about the view that it belonged to the Echinodermata phylum. Dzik (1991) made speculative classifications for some ambiguous fossils and established higher taxonomic units, suggesting that fossils like Eldonia are related to ctenophore (brachiopods) and bryozoans. Chen Junyuan et al. (Chen et al., 1995) re-studied some specimens of Eldonia in the Chengjiang fauna, largely agreeing with Dzik's speculation and placing these jellyfish-like fossils in Dzik's new class—Eldonioidea (Class Eldonioidea Dzik, 1991, non 1989).
The animal body is in the shape of a long-stemmed cup, with a vertical height of over 100 mm, mainly composed of the lower stem, the middle calyx, the upper bracts, and the excretory tube. The stem is slender and tubular, used for attachment and support of the main part of the animal. The calyx cavity is relatively small, resembling a wine glass with a narrow bottom and a wide top. Around the upper edge of the calyx cavity are 18 bracts, which are internally divided into small chamber-like structures by a series of transverse ridges, possibly serving as tentacles or attachment areas for tentacles. The bracts can extend horizontally from their bases, forming a radial pattern centered around the calyx cavity. Near the center of the calyx cavity is a long, upward-extended tubular structure interpreted as the excretory tube. Craspedostoma was originally discovered in the Burgess Shale of Canada. The species from the Chengjiang fauna are better preserved than those from the Burgess Shale, and the number of specimens found is currently greater than those discovered in Canada. Conway Morris (1977) discussed the phylogenetic relationships of Craspedostoma in detail, comparing it with related living phyla and concluding that its systematic position remains unresolved. However, he also suggested that, compared to others, Craspedostoma might be most closely related to modern entoprocts. Dzik (1991) reviewed the taxonomic position of Craspedostoma, concluding that it does not belong to entoprocts but forms a unique evolutionary lineage with jellyfish-like fossils like Eldonia, for which he established the new class Eldonioidea and placed it in the phylum Tentaculata, with affinities to brachiopods and bryozoans with tentacle rings.
The Craspedostoma is a rare species in the Chengjiang fauna, with all discovered specimens preserved individually and scattered, indicating that the animal did not live in clusters but was sparsely distributed on the seabed, using its stem to attach to the seabed or partially burying it in mud. The specimens found show the stem as a straight tube, suggesting that the stem is not easily bendable. The main function of the tentacles on the bracts is likely to capture and collect food.