Timothy P. Topper

Bio: Timothy P. Topper is an academic researcher from Swedish Museum of Natural History. The author has contributed to research in topics: Geology & Cambrian Series 2. The author has an hindex of 20, co-authored 53 publications receiving 1201 citations. Previous affiliations of Timothy P. Topper include Uppsala University & Durham University.

An encrusting kleptoparasite-host interaction from the early Cambrian

Abstract: Parasite–host systems are pervasive in nature but are extremely difficult to convincingly identify in the fossil record. Here we report quantitative evidence of parasitism in the form of a unique, enduring life association between tube-dwelling organisms encrusted to densely clustered shells of a monospecific organophosphatic brachiopod assemblage from the lower Cambrian (Stage 4) of South China. Brachiopods with encrusting tubes have decreased biomass (indicating reduced fitness) compared to individuals without tubes. The encrusting tubes orient tightly in vectors matching the laminar feeding currents of the host, suggesting kleptoparasitism. With no convincing parasite–host interactions known from the Ediacaran, this widespread sessile association reveals intimate parasite–host animal systems arose in early Cambrian benthic communities and their emergence may have played a key role in driving the evolutionary and ecological innovations associated with the Cambrian radiation. Parasitic interactions are difficult to document in the fossil record. Here, Zhang et al. analyze a large population of a Cambrian brachiopod and show it was frequently encrusted by tubes aligned to its feeding currents and that encrustation was associated with reduced biomass, suggesting a fitness cost.

Scleritome construction, biofacies, biostratigraphy and systematics of the tommotiid Eccentrotheca helenia sp. nov. from the Early Cambrian of South Australia

Abstract: Large collections of Eccentrotheca helenia sp. nov. from the lower Cambrian Wilkawillina and Ajax limestones in the Arrowie Basin, South Australia, contain abundant low, cap-shaped and high, laterally compressed isolated sclerites in addition to partially articulated tubular specimens. The scleritome of Eccentrotheca helenia sp. nov. is fully described for the first time and shown to be formed by ontogenetic fusion of sclerites into successively stacked sclerite rings, forming a larger, tubular structure. The apical termination of the tube is highly variable, but is primarily constructed by low, cap-shaped sclerites and characterised by a central aperture of variable inclination. The adapical portion of the tube is predominantly constructed by high, laterally compressed sclerites, but individual sclerite rings can contain both cap-shaped and laterally compressed sclerites along with sclerites of intermediate morphology. The apical aperture presumably housed organic structures for attachment to a hard substrate, but the scleritome also occasionally preserves small lateral perforations between fused sclerites, which may have served to stabilise the scleritome by providing additional points of anchorage. In the Arrowie Basin, E. helenia is found in association with archaeocyath-microbial-spongiomorph-dominated bioherms and most likely inhabited pendant or cryptic habitats within these bioherms. Eccentrotheca-like sclerites form an integral part of the scleritomes of many tommotiids which may confuse taxonomic analysis. Sclerites previously assigned to 'E.' guano, consistently occur together with sclerites of Kulparina rostrata in stratigraphic intervals consistently older than strata hosting E. helenia. Rare fused specimens indicate that the sclerites of K. rostrata and 'E.' guano belong to the same scleritome.

The scleritome of Paterimitra: an Early Cambrian stem group brachiopod from South Australia.

Abstract: Early Cambrian tommotiids are problematic fossil metazoans with external organophosphatic sclerites that have been considered to be basal members of the lophophorate stem group. Tommotiids are almost exclusively known from isolated or rarely fused individual sclerites, which made previous reconstructions of the actual organism highly conjectural. However, the recent discovery of the first articulated specimens of the tommotiid Eccentrotheca revealed a tubular sclerite arrangement (scleritome) that limited the possible life habit to sessile filter feeding and thus further supported a lophophorate affinity. Here, we report the first articulated specimens of a second tommotiid taxon, Paterimitra from the Early Cambrian of the Arrowie Basin, South Australia. Articulated specimens of Paterimitra are composed of two bilaterally symmetrical sclerite types and an unresolved number of small, asymmetrical and irregular crescent-shaped sclerites that attached to the anterior margin of the symmetrical sclerites. Together, the sclerites form an open cone in which the symmetrical sclerites are joined together and form a small posterior opening near the base of the scleritome, while the irregular crescent-shaped sclerites defined a broad anterior opening. The coniform scleritome of Paterimitra is interpreted to have attached to hard substrates via a pedicle that emerged through the small posterior opening (sometimes forming a tube) and was probably a sessile filter feeder. The scleritome of Paterimitra can be derived from the tubular scleritome of Eccentrotheca by modification of basal sclerites and reduction in tube height, and probably represents a more derived member of the brachiopod stem group with the paired symmetrical sclerites possibly homologous to brachiopod valves.

Competition and mimicry: the curious case of chaetae in brachiopods from the middle Cambrian Burgess Shale

Abstract: One of the first phyla to acquire biomineralized skeletal elements in the Cambrian, brachiopods represent a vital component in unraveling the early evolution and relationships of the Lophotrochozoa. Critical to improving our understanding of lophotrochozoans is the origin, evolution and function of unbiomineralized morphological features, in particular features such as chaetae that are shared between brachiopods and other lophotrochozoans but are poorly understood and rarely preserved. Micromitra burgessensis and Paterina zenobia from the middle Cambrian Burgess Shale are among the most remarkable examples of fossilized chaetae-bearing brachiopods. The form, functional morphology, evolutionary and ecological significance of their chaetae are studied herein. Like in Recent forms, the moveable but semi-rigid chaetae fringe both the dorsal and ventral mantle margins, but in terms of length, the chaetae of Burgess Shale taxa can exceed twice the maximum length of the shell from which it projects. This is unique amongst Recent and fossil brachiopod taxa and given their size, prominence and energy investment to the organism certainly had an important functional significance. Micromitra burgessensis individuals are preserved on hard skeletal elements, including conspecific shells, Tubulella and frequently on the spicules of the sponge Pirania muricata, providing direct evidence of an ecological association between two species. Morphological analysis and comparisons with fossil and extant brachiopod chaetae point to a number of potential functions, including sensory, defence, feeding, defouling, mimicry and spatial competition. Our study indicates that it is feasible to link chaetae length to the lack of suitable substrate in the Burgess Shale environment and the increased intraspecific competition associated with this. Our results however, also lend support to the elongated chaetae as an example of Batesian mimicry, of the unpalatable sponge Pirania muricata. We also cannot discount brachiopod chaetae acting as a sensory grille, extending the tactile sensitivity of the mantle into the environment, as an early warning system to approaching predators.

A new species

Abstract: We redescribe the only previously known species of Myrsidea from bulbuls, M. pycnonoti Eichler. Sixteen new species are described; they and their type hosts are: M. phillipsi ex Pycnonotus goiavier goiavier (Scopoli), M. gieferi ex P. goiavier suluensis Mearns, M. kulpai ex P. flavescens Blyth, M. finlaysoni ex P. finlaysoni Strickland, M. kathleenae ex P. cafer (L.), M. warwicki ex Ixos philippinus (J. R. Forster), M. mcclurei ex Microscelis amaurotis (Temminck), M. zeylanici ex P. zeylanicus (Gmelin), M. plumosi ex P. plumosus Blyth, M. eutiloti ex P. eutilotus (Jardine and Selby), M. adamsae ex P. urostictus (Salvadori), M. ochracei ex Criniger ochraceus F. Moore, M. borbonici ex Hypsipetes borbonicus (J. R. Forster), M. johnsoni ex P. atriceps (Temminck), M. palmai ex C. ochraceus, and M. claytoni ex P. eutilotus. A key is provided for the identification of these 17 species.

Review of deep learning: concepts, CNN architectures, challenges, applications, future directions

Abstract: In the last few years, the deep learning (DL) computing paradigm has been deemed the Gold Standard in the machine learning (ML) community. Moreover, it has gradually become the most widely used computational approach in the field of ML, thus achieving outstanding results on several complex cognitive tasks, matching or even beating those provided by human performance. One of the benefits of DL is the ability to learn massive amounts of data. The DL field has grown fast in the last few years and it has been extensively used to successfully address a wide range of traditional applications. More importantly, DL has outperformed well-known ML techniques in many domains, e.g., cybersecurity, natural language processing, bioinformatics, robotics and control, and medical information processing, among many others. Despite it has been contributed several works reviewing the State-of-the-Art on DL, all of them only tackled one aspect of the DL, which leads to an overall lack of knowledge about it. Therefore, in this contribution, we propose using a more holistic approach in order to provide a more suitable starting point from which to develop a full understanding of DL. Specifically, this review attempts to provide a more comprehensive survey of the most important aspects of DL and including those enhancements recently added to the field. In particular, this paper outlines the importance of DL, presents the types of DL techniques and networks. It then presents convolutional neural networks (CNNs) which the most utilized DL network type and describes the development of CNNs architectures together with their main features, e.g., starting with the AlexNet network and closing with the High-Resolution network (HR.Net). Finally, we further present the challenges and suggested solutions to help researchers understand the existing research gaps. It is followed by a list of the major DL applications. Computational tools including FPGA, GPU, and CPU are summarized along with a description of their influence on DL. The paper ends with the evolution matrix, benchmark datasets, and summary and conclusion.

Revised Classification, Nomenclator and Typification of Gastropod and Monoplacophoran Families

Abstract: 2,604 names at the rank of subtribe, tribe, subfamily, family and superfamily have been proposed for Recent and fossil gastropods, and another 35 for monoplacophorans. All names are listed in a nomenclator giving full bibliographical reference, date of publication, typification, and their nomenclatural availability and validity under the International Code of Zoological Nomenclature. Another 790 names, established for categories above the familygroup (infraorder to subclass) are listed separately. A fully ranked, hierarchical classification summarizes recent advances in the phylogeny of the Gastropoda and Monoplacophora. In all, the classification recognizes as valid a total of 721 gastropod families, of which 245 are known exclusively as fossils and 476 occur in the Recent with or without a fossil record; and 20 monoplacophoran families, of which 1 only occurs as Recent.Nomenclatural acts in this work: Amberleya bathonica Cox & Arkell, 1950, fixed as type species of Amberleya J. Morris & Lycett, 1851, under Art. 70.3; Ampezzopleura tenuis Nutzel, 1998, fixed as type species of Ampezzopleura Bandel, 1991, under Art. 70.3; Proserpina nitida G. B. Sowerby II, 1839, designated type species of Despoena Newton, 1891; Buccinum glabratum Linnaeus, 1758, designated type species of Dipsaccus H. Adams & A. Adams, 1853; Murex ficus Linnaeus, 1758, designated type species of Ficula Swainson, 1835; Oncomelania hupensis Gredler, 1881, designated type species of Hemibia Heude, 1890; Murex metaxa Delle Chiaje, 1828, fixed as type species of Metaxia Monterosato, 1884 under Art. 70.3; Neridomus anglicus Cox & Arkell, 1950, fixed as type species of Neridomus J. Morris & Lycett, 1851, under Art. 70.3; Navicella clypeolum Recluz, 1843, designated type species of Orthopoma Gray, 1868; Trochus viadrinus M. Schmidt, 1905, fixed as type species of Parataphrus Chavan, 1954 under Art. 70.3; Helix pomatia Linnaeus, 1758, designated type species of Pentataenia A. Schmidt, 1855; Flammulina ponsonbyi Suter, 1897, fixed as type species of Phenacohelix Suter, 1892, under Art. 70.3; Cyrtolites corniculum Eichwald, 1860, fixed as type species of Pollicina Koken, 1895, under Art. 70.3; Purpurina elegantula d'Orbigny, 1850, designated as type species of Purpurina d'Orbigny, 1850, and lectotype of Turbo bellona d'Orbigny, 1850, designated as neotype of Purpurina elegantula; Pyramidella minuscula Monterosato, 1880, fixed as type species of Tiberia Jeffreys, 1884, under Art. 70.3; Cyclostoma delicatum Philippi, 1844, fixed as type species of Trachysma G. O. Sars, 1878, under Art. 70.3; Helix elegans Gmelin, 1791, fixed as type species of Trochoidea T. Brown, 1827, under Art. 70.3; Turritellopsis stimpsoni Dall, 1919, fixed as type species of Turritellopsis G. O. Sars, 1878, under Art. 70.3; Fusus averillii Gabb, 1864, fixed as type species of Volutoderma Gabb, 1876, under Art. 70.3; Voluta pepo Lightfoot, 1786, fixed as type species of Yetus Bowdich, 1822. Curnonidae d'Udekem d'Acoz, nom. nov., and Curnon d'Udekem d'Acoz, nom. nov., are established for Charcotiidae Odhner, 1926, and Charcotia Vayssiere, 1906, (between 27 March and 1 May), non Charcotia Chevreux, 1906 (January) [Amphipoda]; Yuopisthonematidae Nutzel, nom. nov., and Yuopisthonema Nutzel, nom. nov., are established for Opisthonematidae Yu, 1976, and Opisthonema Yu, 1974, non Gill, 1862 [Pisces]. The new family-group name Burnupiidae Albrecht is established in this work; and the names Scolodontina and Orthalicoidei are first used here to denote, respectively, a suborder containing the family Scolodontidae, and an infraorder containing the superfamily Orthalicoidea.

The earliest Cambrian record of animals and ocean geochemical change

Abstract: The Cambrian diversification of animals was long thought to have begun with an explosive phase at the start of the Tommotian Age. Recent stratigraphic discoveries, however, suggest that many taxa appeared in the older Nemakit-Daldynian Age, and that the diversification was more gradual. We map lowest Cambrian (Nemakit-Daldynian through Tommotian) records of δ 13 C CaCO 3 variability from Siberia, Mongolia, and China onto a Moroccan U/Pb–δ 13 C CaCO 3 age model constrained by five U/Pb ages from interbedded volcanic ashes. The δ 13 C CaCO 3 correlations ignore fossil tie points, so we assume synchroneity in δ 13 C trends rather than synchroneity in first appearances of animal taxa. We present new δ 13 C org , 87 Sr/ 86 Sr, uranium, and vanadium data from the same carbonate samples that define the Moroccan δ 13 C CaCO 3 curve. The result is a new absolute time line for first appearances of skeletal animals and for changes in the carbon, strontium, and redox chemistry of the ocean during the Nemakit-Daldynian and Tommotian ages at the beginning of the Cambrian. The time line suggests that the diversification of skeletal animals began early in the Nemakit-Daldynian, with much of the diversity appearing by the middle of the age. Fossil first appearances occurred in three pulses, with a small pulse in the earliest Nemakit-Daldynian (ca. 540–538 Ma), a larger pulse in the mid- to late Nemakit-Daldynian (ca. 534–530 Ma), and a moderate pulse in the Tommotian (ca. 524–522 Ma). These pulses are associated with rapid reorganizations of the carbon cycle, and are superimposed on long-term increases in sea level and the hydrothermal flux of Sr.