When a 520 million-year-old Chengjiang fossil meets a modern micro-CT - a case study

The 520 million-year-old Chengjiang biota of China (UNESCO World Heritage) presents the earliest known evidence of the so-called Cambrian Explosion. Studies, however, have mainly been limited to the information exposed on the surface of the slabs. Thus far, structures preserved inside the slabs were accessed by careful removal of the matrix, in many cases with the unfortunate sacrifice of some "less important" structures, which destroys elements of exceptionally preserved specimens. Here, we show for the first time that microtomography (micro-CT) can reveal structures situated inside a Chengjiang fossil slab without causing any damage. In the present study a trilobitomorph arthropod (Xandarella spectaculum) can be reliably identified only with the application of micro-CT. We propose that this technique is an important tool for studying three-dimensionally preserved Chengjiang fossils and, most likely, also those from other biota with a comparable type of preservation, specifically similar iron concentrations

A 520 million-year-old chelicerate larva

An important survival strategy for animal species is the so-called niche differentiation between larva and adult. Different developmental stages of the same animal occupy different ecological niches to avoid competing for food or other essential resources. Here, we describe an exceptionally preserved larval stage of the short great appendage (SGA) arthropod (megacheiran) Leanchoilia illecebrosa from the early Cambrian Chengjiang biota of China. The larval specimen preserves fine details of the main feeding limb, the SGA, which are unknown in the adult of the same species. This discovery demonstrates that niche differentiation during ontogeny was developed in this species of megacheiran-a group of fossil arthropods that has been considered to be early representatives of Chelicerata, which includes horseshoe crabs and arachnids. Hence, this type of niche differentiation, which is common today, originated from the early Cambrian

Cambrian Sessile, Suspension Feeding Stem-Group Ctenophores and Evolution of the Comb Jelly Body Plan

The origin of ctenophores (comb jellies) is obscured by their controversial phylogenetic position, with recent phylogenomic analyses resolving either sponges or ctenophores as the sister group of all other animals. Fossil taxa can provide morphological evidence that may elucidate the origins of derived characters and shared ancestries among divergent taxa, providing a means to “break” long branches in phylogenetic trees. Here we describe new fossil material from the early Cambrian Chengjiang Biota, Yunnan Province, China, including the putative cnidarian Xianguangia, the new taxon Daihua sanqiong gen et sp. nov., and Dinomischus venustus, informally referred to as “dinomischids” here. “Dinomischids” possess a basal calyx encircled by 18 tentacles that surround the mouth. The tentacles carry pinnules, each with a row of stiff filamentous structures interpreted as very large compound cilia of a size otherwise only known in ctenophores. Together with the Cambrian tulip animal Siphusauctum and the armored Cambrian scleroctenophores, they exhibit anatomies that trace ctenophores to a sessile, polypoid stem lineage. This body plan resembles the polypoid, tentaculate morphology of cnidarians, including a blind gastric cavity partitioned by mesenteries. We propose that comb rows are derived from tentacles with paired sets of pinnules that each bear a row of compound cilia. The scleroctenophores exhibit paired comb rows, also observed in Siphusauctum, in addition to an organic skeleton, shared as well by Dinomischus, Daihua, and Xianguangia. We formulate a hypothesis in which ctenophores evolved from sessile, polypoid suspension feeders, sharing similarities with cnidarians that suggest either a close relationship between these two phyla, a striking pattern of early convergent evolution, or an ancestral condition for either metazoans or eumetazoans

Efficient photocatalytic hydrogen peroxide production over TiO2 passivated by SnO2

Photocatalysis provides an attractive strategy for synthesizing H2O2 at ambient condition. However, the photocatalytic synthesis of H2O2 is still limited due to the inefficiency of photocatalysts and decomposition of H2O2 during formation. Here, we report SnO2-TiO2 heterojunction photocatalysts for synthesizing H2O2 directly in aqueous solution. The SnO2 passivation suppresses the complexation and decomposition of H2O2 on TiO2. In addition, loading of Au cocatalyst on SnO2-TiO2 heterojunction further improves the production of H2O2. The in situ electron spin resonance study revealed that the formation of H2O2 is a stepwise single electron oxygen reduction reaction (ORR) for Au and SnO2 modified TiO2 photocatalysts. We demonstrate that it is feasible to enhance H2O2 formation and suppress H2O2 decomposition by surface passivation of the H2O2-decomposition-sensitive photocatalysts

Exites in Cambrian arthropods and homology of arthropod limb branches

Abstract: The last common ancestor of all living arthropods had biramous postantennal appendages, with an endopodite and exopodite branching off the limb base. Morphological evidence for homology of these rami between crustaceans and chelicerates has, however, been challenged by data from clonal composition and from knockout of leg patterning genes. Cambrian arthropod fossils have been cited as providing support for competing hypotheses about biramy but have shed little light on additional lateral outgrowths, known as exites. Here we draw on microtomographic imaging of the Cambrian great-appendage arthropod Leanchoilia to reveal a previously undetected exite at the base of most appendages, composed of overlapping lamellae. A morphologically similar, and we infer homologous, exite is documented in the same position in members of the trilobite-allied Artiopoda. This early Cambrian exite morphology supplements an emerging picture from gene expression that exites may have a deeper origin in arthropod phylogeny than has been appreciated.Copyright © The Authors, 2021. This is an open access article, available to all readers online, published under a creative commons licensing (https://creativecommons.org/licenses/by/4.0/). The attached file is the published version of the article

The functional head of the Cambrian radiodontan (stem-group Euarthropoda) Amplectobelua symbrachiata

© The Author(s). 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. The attached file is the published version of the article

Experimental taphonomy of velvet worms (Onychophora) and implications for the Cambrian “explosion, disparity and decimation” model

Experimental preservation of velvet worms (phylum Onychophora), a very rare but evolutionarily important group that has existed for more than 500 million years, showed that the absence of bucal parts, adhesive- expelling organs, gonopore, eyes, legs, claws, annulation and papillation in fossils may not represent absence in the living animals. In fossils, leg thickness and claw orientation can be unreliable. The experiments indicate that not only absence, but even presence of certain structures can simply be the result of tissue decomposition. Computer-aided photorealistic reconstructions of fossil onychophorans are presented. We recommend future researchers to conduct taphonomy experiments specially before analysing unusual fossils.La preservación experimental de los gusanos “aterciopelados” u onicóforos (Phylum Onychophora), un grupo poco común pero evolutivamente importante que ha existido por más de 500 millones de años, mostró que la ausencia de partes bucales, glándulas secretoras de adhesivo, gonoporo, ojos, patas, garras, anulación cuticular y papilas en los fósiles, puede no representar la ausencia de tales órganos en los organismos vivos. No son confiables el grueso de las patas y la orientación de las garras (uñas), pues se modifican durante la preservación. Los experimentos indican que no sólo la ausencia, sino también la presencia de ciertas estructuras pueden ser simplemente resultado de la descomposición de los tejidos. Se presentan reconstrucciones fotorrealistas computarizadas de onicóforos fósiles. Para futuras investigaciones, recomendamos conducir experimentos tafonómicos previos al análisis del material preservado, especialmente antes de analizar fósiles poco comunes

Disparity, decimation and the Cambrian "explosion": comparison of eady Cambrian and Present faunal communities with emphasis on velvet worms (Onychophora)

The controversy about a Cambrian " explosion" of morphological disparity (followed by decimation), eladogenesis and fossilization is of central importanee for the history of life. This p aper revisits the controversy (with emphasis in onychophorans, which inelude emblematic organisms such as Hallucigenia), presents new data about the Chengjiang (Cambrian of China) faunal community and compares it and Ihe Burgess Shale (Cambrian of Canada) with an ecologically similar bul modern tropical marine site where onychophorans are absent, and with a modern neo tropical terrestrial onychophoran community. B i ovolume was estimated from material collected in Costa Rica and morphometric measurements were made on enlarged images of fossils. CaJTlbrian tropical mudflats were characterized by the adaptive radiation of two contrasting groups: the vagile arthropods and the sessile poriferans. Arthropods were later replaced as the dominant benthic laxon by polychaetes. Vagility and the exoskeleton may explain the success of arthropods from the Cambrian to the modern marine and terrestrial communities, both in population and biovolume. Food ecological displacement was apparen t i n the B. Shale, but not in Chengjiang or the terrestrial community. When only hard parts were preserved, marine and terrestrial fossil deposits of tropical origin are even less representative than deposits produced by temperate taxa, Chengjiang being an exception. Nutrient limitations might explain why deposit feeding is less important in terrestrial onychophoran communities, where carnivory, scavenging and omnivory (associated with high motility and life over the substrate) became moreimportant. Fossil morphometry supports the interpretation of "lobopod animal s" as onychophorans, whose abundance in Chengjiang was equal lo their abundance in modern communities. The extinction of marine onychophorans may reflect domination of the infaunal habitat by polychaetes. We conclude tha! ( 1 ) a mature ecological community structure was generalized during the Cambrian, and even biodiversity and equitability indices were surprisingly elose lo modern values; (2) the morphological diversity and geographic distribution of onychophorans indicate a significant pre-Cambrian evolutionary history which does no! support the "explosion" hypothesis; (3) disparity among phyla was not as important as the explosion-decimation model predicIs, bu! in the case of onychophorans, disparíty wÍlhin the phylum was greater than it is today and ¡ts reduction may have been associated with migration into the sedi ment when large predators evolved.Con base en nuevos hallazgos paleontológicos hechos en el sur de China se analiza la controversia sobre la "explosión del Cámbrico" que supuestamente incluyó un gran aumento en la diversidad morfológica, con la aparición de muchos filos que posteriormente se extinguieron . Se compara las comunidades fósiles de Cheng-yiang (China) y Burgess S hale (Canadá) con una comunidad marina similar moderna (Punta Morales, Costa Rica) y con una comunidad terrestre moderna (Coronado, Costa Rica) que al igual que los dos depósitos fosilíferos incluye al filo Onychophora. Se concluye que ( 1 ) durante el Cámbrico las comunidades costeras tropicales eran similares a las modernas al punto de que incluso los índices de biodiversidad y equitabilidad eran semejantes a los actuales; (2) la diversidad morfológica y distribución geográfica de los onicóforos indican una larga historia evolutiva precámbrica que no apoya el modelo de la "explosión"; (3) las diferencias morfológicas entre filos no eran tan importantes como predice el modelo de "explosión seguida de extinción", pero en la caso de los onicóforos, la diversidad morfológica dentro del jilo era mayor en el Cámbrico que en la actualidad, y su reducción puede haber estado asociada con la migración al interior del sedimento al evolucionar depredadores de tamaño relativamente grande