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Burgess Shale-type fossil Lagerstätten provide the best evidence for deciphering the biotic patterns and magnitude of the Cambrian explosion. Here, we report a Lagerstätte from South China, the Qingjiang biota (~518 million years old), which is dominated by soft-bodied taxa from a distal shelf setting. The Qingjiang biota is distinguished by pristine carbonaceous preservation of labile organic features, a very high proportion of new taxa (~53%), and preliminary taxonomic diversity that suggests it could rival the Chengjiang and Burgess Shale biotas. Defining aspects of the Qingjiang biota include a high abundance of cnidarians, including both medusoid and polypoid forms; new taxa resembling extant kinorhynchs; and abundant larval or juvenile forms. This distinctive composition holds promise for providing insights into the evolution of Cambrian ecosystems across environmental gradients., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

The Lophotrochozoa includes disparate tentacle-bearing sessile protostome animals, which apparently appeared in the Cambrian explosion, but lack an uncontested fossil record. Here we describe abundant well preserved material of Cotyledion tylodes Luo et Hu, 1999, from the Cambrian (Series 2) Chengjiang deposits, reinterpreted here as a stem-group entoproct. The entoproct affinity is supported by the sessile body plan and interior soft anatomy. The body consists of an upper calyx and a lower elongate stalk with a distal holdfast. The soft anatomy includes a U-shaped gut with a mouth and aboral anus ringed by retractable marginal tentacles. Cotyledion differs from extant entoprocts in being larger, and having the calyx and the stalk covered by numerous loosely-spaced external sclerites. The description of entoprocts from the Chengjiang biota traces the ancestry of yet another lophotrochozoan phylum back to the Cambrian radiation, and has important implications for the earliest evolution of lophotrochozoans.

Burgess Shale-type deposits provide a wealth of information on the early evolution of animals. Questions that are central to understanding the exceptional preservation of these biotas and the paleoenvironments they inhabited may be obscured by the post-depositional alteration due to metamorphism at depth and weathering near the Earth's surface. Among over 50 Cambrian BST biotas, the Chengjiang and Qingjiang deposits are well known for their richness of soft-bodied taxa, fidelity of preservation, and Early Cambrian Age. While alteration via weathering has been well-investigated, the thermal maturity of the units bearing the two biotas has not yet been elucidated. Here we investigate peak metamorphic temperatures of the two deposits using two independent methods. Paleogeotemperature gradient analyses demonstrate that the most fossiliferous sections of the Chengjiang were buried at a maximum depth of ∼8 500 m in the Early Triassic, corresponding to ∼300 °C, while the type area of the Qingjiang biota was buried at a maximum depth of ∼8 700 m in the Early Jurassic, corresponding to ∼240 °C. Raman geothermometer analyses of fossil carbonaceous material demonstrate that peak temperatures varied across localities with different burial depth. The two productive sections of the Chengjiang biota were thermally altered at a peak temperature of approximately 300 °C, and the main locality of the Qingjiang biota experienced a peak temperature of 238 ± 22 °C. These results from two independent methods are concordant. Among BST deposits for which thermal maturity has been documented, the Qingjiang biota is the least thermally mature, and therefore holds promise for enriching our understanding of BST deposits. [ABSTRACT FROM AUTHOR]

Retifacies abnormalis is a large artiopodan euarthropod known only from the famous fossil deposits of the Chengjiang biota, China (Cambrian Series 2, Stage 3). It is well known for its pronounced reticulated ornamentation that covers the entire dorsal surface of the exoskeleton. Here 109 new specimens of R. abnormalis from multiple deposits are reported. Some larger specimens display a distinct carapace ornamentation to what was previously known. By qualitatively separating specimens into two groups ('Morph A', 'Morph B') and analyzing the shape of the body, pygidium, and shape of the polygons in the reticulation, using linear and geometric morphometrics and elliptical Fourier analysis, the two morphs are shown to overlap in morphospace and display similar length:width ratios of body parts, rather than form two distinct clusters. The differences are interpreted as intraspecific rather than as diagnosing two species. As Morph B are only found in larger size classes, R. abnormalis ornamentation differences are interpreted to have developed during ontogeny, but are not thought to represent sexual dimorphs. [ABSTRACT FROM AUTHOR]