Soft part preservation in hyolithids from the lower Cambrian (Stage 4) Guanshan Biota of South China and its implications

• Published in: Palaeogeography, palaeoclimatology, palaeoecology palaeoclimatology, palaeoecology, 2021-01, Vol.562, p.110079, Article 110079
• Main Authors: Liu, Fan, Skovsted, Christian B., Topper, Timothy P., Zhang, ZhiFei
• Format: Article
• Language: English
• Subjects: biofilm; Cambrian period; Cambrian Series 2; China; Den föränderliga jorden; digestive tract; Digestive tracts; exoskeleton; Hyolitha; Konservat-Lagerstätten; muscles; Ordovician period; palaeogeography; paleoclimatology; paleoecology; Permian period; phylogeny; Taphonomy; The changing Earth
• ISSN: 0031-0182; 1872-616X; 1872-616X
• DOI: 10.1016/j.palaeo.2020.110079

Hyoliths, known globally from the Cambrian to the Permian are generally recognized as early lophotrochozoan animals of uncertain phylogenetic position. The calcareous exoskeleton of hyolithids, one of the two subgroups of hyoliths, consist of four elements including a conical conch, an external operculum, and a pair of curved enigmatic helens, but their ecology and internal morphology have long been considered controversial. Here we present for the first time, remarkably preserved hyolithids with helens and interior soft tissues from the Guanshan Biota (Cambrian, Stage 4) of Shijiangjun section, Wuding County in eastern Yunnan Province of South China. Preserved soft tissues and organs encompass the digestive tract, muscle scars and connective tissues between the operculum and conch. Three modes of soft part preservation in hyolithids from the Guanshan Biota are described: (1) preservation through pyritization, (2) sediment-infilling of guts, and (3) bacterial biofilm pseudomorphs (expressed as large internal hollow cavities), resulting from endogenous bacterial decay of soft parts. Such differential preservation of hyolith guts indicates different taphonomic modes for the soft parts of Cambrian animals in the Guanshan Biota. The newly collected material yields the oldest preserved guts in hyolithids from Konservat-biotas, and reveals new evidence for reconstructing hyolithid anatomy, such as the articulation mechanism of the opercula and the internal structures in the conch. Comparisons with younger well-preserved hyolithid specimens indicate that the gut anatomy of hyolithids was evolutionarily conservative from the early Cambrian through to at least the Ordovician. [Display omitted] •New exceptional specimens of hyolithids from the Guanahan biota are reported.•Extraordinary soft parts are preserved including muscle scars and digestive tracts.•The co-occurrence of three types of preservation modes for the hyolithid gut is unique.•Hyolithids have a stable evolution at least from the Cambrian to the Ordovician.