DOCSLIB.ORG

Morphometric Analysis of Cambrian Fossils and Its Evolutionary Significance

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Morphometric Analysis of Cambrian Fossils and Its Evolutionary Significance Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1506 Morphometric analysis of Cambrian fossils and its evolutionary significance ILLIAM JACKSON ACTA UNIVERSITATIS UPSALIENSIS ISSN 1651-6214 ISBN 978-91-554-9894-8 UPPSALA urn:nbn:se:uu:diva-319487 2017 Dissertation presented at Uppsala University to be publicly examined in Norrlands 1 & 2, Villavägen 16, Uppsala, Friday, 2 June 2017 at 13:00 for the degree of Doctor of Philosophy. The examination will be conducted in English. Faculty examiner: Professor Nigel Hughes (University of California, Riverside). Abstract Jackson, I. 2017. Morphometric analysis of Cambrian fossils and its evolutionary significance. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1506. 63 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-554-9894-8. The Extended Evolutionary Synthesis (EES) is currently emerging as a theoretical alternative to the Modern Synthesis (MS) in which to frame evolutionary observations and interpretations. These alternative frameworks differ fundamentally in their understanding of the relative roles of the genotype, phenotype, development and environment in evolutionary processes and patterns. While the MS represents a gene-centred view of evolution, the EES instead emphasizes the interactions between organism, development and environment. This novel theoretical framework has generated a number of evolutionary predictions that are mutually incompatible with the equivalent of the MS. While research and empirical testing has begun on a number of these in a neontological context, the field of palaeontology has yet to contribute meaningfully to this endeavour. One of the reasons for this is a lack of methodological approaches capable of investigating relevant evolutionary patterns in the fossil record. In this thesis morphometric methods capable of providing relevant data are developed and employed in the analysis of Cambrian fossils. Results of these analyses provide empirical support for the process of evolution through phenotypic plasticity and genetic assimilation hypothesized by the EES. Furthermore, theoretical revision to the species concept in a palaeontological context is suggested. Finally, predictions of the EES specific to the fossil record are made explicit and promising directions of future research are outlined. Keywords: Extended Evolutionary Synthesis, phenotypic plasticity, genetic assimilation, phenotypic accommodation, Agnostus pisiformis, Mackinnonia, elliptical fourier analysis, species concept Illiam Jackson, Department of Earth Sciences, Palaeobiology, Villav. 16, Uppsala University, SE-75236 Uppsala, Sweden. © Illiam Jackson 2017 ISSN 1651-6214 ISBN 978-91-554-9894-8 urn:nbn:se:uu:diva-319487 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-319487) For Steph List of Papers This thesis is based on the following papers, which are referred to in the text by their Roman numerals: I Jackson, I. S. C. & Budd, G. E. (2017) Intraspecific morpholog- ical variation of Agnostus pisiformis, a Cambrian Series 3 trilo- bite-like arthropod. Lethaia, published online 15 March 2017. doi:10.1111/let.12201 II Jackson, I. S. C. & Claybourn, T. M. (manuscript submitted to Palaeontology) Morphometric Analysis of the Early Cambrian mollusc Mackinnonia and the Incipient Species Concept. III Jackson, I. S. C., Bohlin, M. S., Mann, R. P., Budd, G. E. (man- uscript submitted to Nature) Genetic assimilation in the fossil record: phenotypic plasticity and accommodation in Cambrian arthropods. IV Jackson, I. S. C. & Budd, G. E. (manuscript) The Extended Evo- lutionary Synthesis in the fossil record. Additionally, the following paper was prepared during the course of the PhD, but is not included in the thesis: I Budd, G. E. & Jackson, I. S. C. (2016) Ecological innovations in the Cambrian and the origins of the crown group phyla. Philo- sophical Transactions of the Royal Society B 371, 20150287. doi:10.1098/rstb.2015.0287 Reprints were made with permission from the respective publishers. Statement of authorship Paper I: I. J. collected the material and conducted the analyses, and interpreted the results and authored the paper with input from G. B. Paper II: I. J. analysed the material, and interpreted the results and co-authored the paper together with T. C. Paper III: I. J. collected material and conducted the morphometric analyses, and co-authored the bulk of the paper together with G. B. Paper IV: I. J. authored the paper with input from G. B. Contents Introduction ..................................................................................................... 9 Organismal variation is continuous .............................................................. 11 A brief history of classification ................................................................ 11 Phylogenetics ........................................................................................... 12 Morphometrics and stratophenetics .......................................................... 17 Morphometric methods ............................................................................ 22 Summary .................................................................................................. 23 Case study ................................................................................................ 23 The morphological variation of Mackinnonia .............................................. 24 Helcionelloida .......................................................................................... 24 Mackinnonia ............................................................................................. 24 Morphological variation and the incipient species concept ..................... 25 Natural selection acts on the phenotype ........................................................ 28 The level of selection ............................................................................... 28 The Extended Evolutionary Synthesis ..................................................... 29 Evolution through phenotypic plasticity and genetic assimilation ........... 31 Macroevolutionary patterns ...................................................................... 33 Quantum evolution ................................................................................... 35 Summary .................................................................................................. 39 Case study ................................................................................................ 40 The phenotypic plasticity of Agnostus pisiformis ......................................... 41 Agnostus pisiformis .................................................................................. 41 Intraspecific variation ............................................................................... 42 Patterns of phenotypic plasticity and genetic assimilation ....................... 43 Conclusion .................................................................................................... 47 Organismal variation is continuous .......................................................... 47 Natural selection acts on the phenotype ................................................... 47 Future directions ........................................................................................... 49 Morphometrics in the fossil record .......................................................... 49 Cambrian explosion .................................................................................. 49 Svensk Sammanfattning ................................................................................ 51 Introduktion .............................................................................................. 51 Evolution genom fenotypisk plasticitet och genetisk assimilation ........... 52 Variation som ett kontinuerligt spektrum ................................................. 52 Morfologisk variation hos Mackinnonia .................................................. 53 Fenotypisk plasticitet och genetisk assimilation hos Agnostus pisiformis .................................................................................................. 53 Slutsatser och framtidsutsikter ................................................................. 54 Acknowledgements ....................................................................................... 55 References ..................................................................................................... 57 Introduction Scientific research takes place within a theoretical framework, which can be defined as a set of implicit or explicit assumptions, conceptualizations and perspectives. This framework determines both the research questions that can be explored and the methods that can be developed. These are interdependent; novel perspectives permit the development of new methodologies and new methodologies make possible the investigation of novel research questions. It is essential, therefore, from time to time to critically review the framework in which a field of research is being conducted and to evaluate how this frame- work is affecting the scope and potential of the research within that field. The Extended Evolutionary Synthesis (EES; Laland et al., 2015) is one such currently emerging reevaluation of a theoretical framework. Specifically it seeks to revise or extend the Modern Synthesis (MS) in evolutionary biol- ogy. Although this sounds dramatic,
Load more

Recommended publications
  • Shell Microstructures in Early Cambrian Molluscs
    Shell microstructures in Early Cambrian molluscs ARTEM KOUCHINSKY Kouchinsky, A. 2000. Shell microstructures in Early Cambrian molluscs. - Acta Palaeontologica Polonica 45,2, 119-150. The affinities of a considerable part of the earliest skeletal fossils are problematical, but investigation of their microstructures may be useful for understanding biomineralization mechanisms in early metazoans and helpful for their taxonomy. The skeletons of Early Cambrian mollusc-like organisms increased by marginal secretion of new growth lamel- lae or sclerites, the recognized basal elements of which were fibers of apparently aragon- ite. The juvenile part of some composite shells consisted of needle-like sclerites; the adult part was built of hollow leaf-like sclerites. A layer of mineralized prism-like units (low aragonitic prisms or flattened spherulites) surrounded by an organic matrix possibly existed in most of the shells with continuous walls. The distribution of initial points of the prism-like units on a periostracurn-like sheet and their growth rate were mostly regular. The units may be replicated on the surface of internal molds as shallow concave poly- gons, which may contain a more or less well-expressed tubercle in their center. Tubercles are often not enclosed in concave polygons and may co-occur with other types of tex- tures. Convex polygons seem to have resulted from decalcification of prism-like units. They do not co-occur with tubercles. The latter are interpreted as casts of pore channels in the wall possibly playing a role in biomineralization or pits serving as attachment sites of groups of mantle cells. Casts of fibers and/or lamellar units may overlap a polygonal tex- ture or occur without it.
    [Show full text]
  • Durham Research Online
    Durham Research Online Deposited in DRO: 23 May 2017 Version of attached le: Accepted Version Peer-review status of attached le: Peer-reviewed Citation for published item: Betts, Marissa J. and Paterson, John R. and Jago, James B. and Jacquet, Sarah M. and Skovsted, Christian B. and Topper, Timothy P. and Brock, Glenn A. (2017) 'Global correlation of the early Cambrian of South Australia : shelly fauna of the Dailyatia odyssei Zone.', Gondwana research., 46 . pp. 240-279. Further information on publisher's website: https://doi.org/10.1016/j.gr.2017.02.007 Publisher's copyright statement: c 2017 This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ Additional information: Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full DRO policy for further details. Durham University Library, Stockton Road, Durham DH1 3LY, United Kingdom Tel : +44 (0)191 334 3042 | Fax : +44 (0)191 334 2971 https://dro.dur.ac.uk Accepted Manuscript Global correlation of the early Cambrian of South Australia: Shelly fauna of the Dailyatia odyssei Zone Marissa J.
    [Show full text]
  • EXPERIMENTAL EVIDENCE for SALTATIONAL CHROMOSOME EVOLUTION in CAL YCADENIA PAUCIFLORA GRAY (ASTERACEAE) Pauciflora Are Fairly Fe
    Heredity (1980), 45 (1), 107-112 0018-067X/80/01940107$02.0O 1980. The Genetical Society of Great Britain EXPERIMENTALEVIDENCE FOR SALTATIONAL CHROMOSOME EVOLUTION IN CAL YCADENIA PAUCIFLORA GRAY (ASTERACEAE) GERALD D. CARR Department of Botany, University of Hawaii, 3190 Maile Way, Honolulu, Hawaii 96822, U.S.A. Received14.i.80 SUMMARY The fertility of the F1 structural heterozygote formed by crossing two aneuploid chromosome races of Calycadenia pauciflora is high despite the fact they are differentiated by the equivalent of three chromosome translocations. This and the fact that ancestral and derived structural homozygotes were recovered in experimental F2 and F3 progenies support the hypothesis that the derived race could have originated directly from the ancestral race in nature through a single saltational event involving multiple chromosome breaks. Two individuals with structurally unique, recombined chromosomes were also recovered in the F2 and the evolutionary potential of such products of meiosis in structural heterozygotes is considered to be significant. 1. INTRODUCTION THERE have been several experimental studies documenting the existence of pairs or groups of diploid plant species differentiated by little more than chromosome alterations, often accompanied by aneuploidy. Calycadenia, Chaenactis, Clarkia and Crepis are just a few of the genera in which this situation is best known or more frequent. In Clarkia, Lewis (1966) referred to this process of differentiation as saltational speciation. Others have used the term quantum evolution or quantum speciation in reference to this general phenomenon (cf. Grant, 1971). This type of chromosomal evolution requires that a new structural heterozygote pass through a "bottleneck of sterility" before the derived structural homozygote can be produced (cf.
    [Show full text]
  • Tempo and Mode in the Macroevolutionary Reconstruction of Darwinism STEPHEN JAY GOULD Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138
    Proc. Nadl. Acad. Sci. USA Vol. 91, pp. 6764-6771, July 1994 Colloquium Paper This paper was presented at a coloquium ented "Tempo and Mode in Evolution" organized by Walter M. Fitch and Francisco J. Ayala, held January 27-29, 1994, by the National Academy of Sciences, in Irvine, CA. Tempo and mode in the macroevolutionary reconstruction of Darwinism STEPHEN JAY GOULD Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138 ABSTRACT Among the several central nings of Dar- But conceptual complexity is not reducible to a formula or winism, his version ofLyellian uniformitranism-the extrap- epigram (as we taxonomists of life's diversity should know olationist commitment to viewing causes ofsmall-scale, observ- better than most). Too much ink has been wasted in vain able change in modern populations as the complete source, by attempts to define the essence ofDarwin's ideas, or Darwin- smooth extension through geological time, of all magnitudes ism itself. Mayr (1) has correctly emphasized that many and sequences in evolution-has most contributed to the causal different, if related, Darwinisms exist, both in the thought of hegemony of microevolutlon and the assumption that paleon- the eponym himself, and in the subsequent history of evo- tology can document the contingent history of life but cannot lutionary biology-ranging from natural selection, to genea- act as a domain of novel evolutionary theory. G. G. Simpson logical connection of all living beings, to gradualism of tried to combat this view of paleontology as theoretically inert change. in his classic work, Tempo and Mode in Evolution (1944), with It would therefore be fatuous to claim that any one legit- a brilliant argument that the two subjects of his tide fall into a imate "essence" can be more basic or important than an- unue paleontological domain and that modes (processes and other.
    [Show full text]
  • Darwinian Evolution and Quantum Evolution
    tics: Cu ne rr e en Nemer et al., Hereditary Genet 2017, 6:2 G t y R r e a t s i e DOI: 10.4172/2161-1041.1000181 d a e r r c e h H Hereditary Genetics ISSN: 2161-1041 Research Article Open Access Darwinian Evolution and Quantum Evolution are Complementary: A Perspective Georges Nemer1, Christina Bergqvist2 and Mazen Kurban1,2,3* 1Department of Biochemistry and Molecular Genetics, American University of Beirut, Beirut, Lebanon 2Department of Dermatology, American University of Beirut, Beirut, Lebanon 3Department of Dermatology, Columbia University, New York, USA Abstract Evolutionary biology has fascinated scientists since Charles Darwin who cornered the concept of natural selection in the 19th century. Accordingly, organisms better adapted to their environment tend to survive and produce more offspring; in other terms, randomly occurring mutations that render the organism more fit to survival will be carried on and be transmitted to the offspring. Nearly a century later, science has seen the discovery of quantum mechanics, the branch of mechanics that deals with subatomic particles. Along with it, came the theory of quantum evolution whereby quantum effects can bias the process of mutation towards providing an advantage for organism survival. This is consistent with looking at the biological system as being a product of chemical-physical reactions, such that chemical structures arrange according to physical laws to form a replicative material referred to as the DNA. In this report, we attempt to reconcile both theories, trying to demonstrate that they complement each other, hoping to fill the gaps in our understandings of the versatility of the mutational status of the DNA as an essential mechanism of life compatibility.
    [Show full text]
  • Quantum Microbiology
    Curr. Issues Mol. Biol. 13: 43-50. OnlineQuantum journal at http://www.cimb.orgMicrobiology 43 Quantum Microbiology J. T. Trevors1* and L. Masson2* big bang. Currently, one of the signifcant unsolved problems in modern physics is how to merge the two into a unifying 1School of Environmental Sciences, University of Guelph, theory. Since quantum mechanics describes the physical 50 Stone Rd., East, Guelph, Ontario N1G 2W1, Canada world, and living organisms are physical entities, it is rational 2Biotechnology Research Institute, National Research and logical to examine the role of quantum mechanics in Council of Canada, 6100 Royalmount Ave., Montreal, the matter and energy of living microorganisms, especially Quebec H4P 2R2, Canada their origin about 4 billion years ago. To do so requires an understanding of quantum processes at the atomic scale and smaller where electrons, for example, do not collide Abstract with the atomic nucleus but defy electromagnetism and orbit During his famous 1943 lecture series at Trinity College at both an undefned speed and path around the nucleus. Dublin, the reknown physicist Erwin Schrödinger discussed One distinguishing characteristic of quantum mechanics the failure and challenges of interpreting life by classical is the Complementarity Principle (or wave-particle duality) physics alone and that a new approach, rooted in Quantum developed by Niels Bohr indicating that a particle can principles, must be involved. Quantum events are simply a possess multiple contradictory properties. level of organization below the molecular level. This includes A classic example of complementarity is Thomas the atomic and subatomic makeup of matter in microbial Young's famous light interference, and later on the double- metabolism and structures, as well as the organic, genetic slit, experiment showing that light or other quantum information codes of DNA and RNA.
    [Show full text]
  • Evolution in the Weak-Mutation Limit: Stasis Periods Punctuated by Fast Transitions Between Saddle Points on the Fitness Landscape
    Evolution in the weak-mutation limit: Stasis periods punctuated by fast transitions between saddle points on the fitness landscape Yuri Bakhtina, Mikhail I. Katsnelsonb, Yuri I. Wolfc, and Eugene V. Kooninc,1 aCourant Institute of Mathematical Sciences, New York University, New York, NY 10012; bInstitute for Molecules and Materials, Radboud University, NL-6525 AJ Nijmegen, The Netherlands; and cNational Center for Biotechnology Information, National Library of Medicine, NIH, Bethesda, MD 20894 Contributed by Eugene V. Koonin, December 16, 2020 (sent for review July 24, 2020; reviewed by Sergey Gavrilets and Alexey S. Kondrashov) A mathematical analysis of the evolution of a large population occur (9, 10). The long intervals of stasis are punctuated by short under the weak-mutation limit shows that such a population periods of rapid evolution during which speciation occurs, and the would spend most of the time in stasis in the vicinity of saddle previous dominant species is replaced by a new one. Gould and points on the fitness landscape. The periods of stasis are punctu- Eldredge emphasized that PE was not equivalent to the “hopeful ated by fast transitions, in lnNe/s time (Ne, effective population monsters” idea, in that no macromutation or saltation was proposed size; s, selection coefficient of a mutation), when a new beneficial to occur, but rather a major acceleration of evolution via rapid mutation is fixed in the evolving population, which accordingly succession of “regular” mutations that resulted in the appearance of moves to a different saddle, or on much rarer occasions from a instantaneous speciation, on a geological scale.
    [Show full text]
  • Shell Microstructure and Its Inheritance in the Calcitic Helcionellid Mackinnonia
    Estonian Journal of Earth Sciences, 2015, 64, 1, 99–104 doi: 10.3176/earth.2015.18 Shell microstructure and its inheritance in the calcitic helcionellid Mackinnonia Michael J. Vendrascoa,b and Antonio G. Checaa a Departamento de Estratigrafía y Paleontología, Avenida Fuentenueva s/n, Universidad de Granada, 18071, Spain; [email protected] b Department of Biological Science, California State University, Fullerton, 92834, USA Received 2 July 2014, accepted 16 December 2014 Abstract. Mackinnonia davidi from the Cambrian (Series 2) of Australia has a prismatic outer shell layer and, as newly described here, a calcitic semi-nacre inner layer. The pattern is the same as in stenothecids such as Mellopegma, providing more evidence for a strong phylogenetic signal in the shell microstructure of Cambrian molluscs. In addition, calcite now appears to have been common in helcionellids and other molluscs during the early and middle Cambrian, with many species exhibiting foliated calcite. This is surprising given the dominance of aragonite in molluscs, both modern and from post-Cambrian fossil deposits with exceptional shell microstructure preservation, including localities from the Ordovician of the Cincinnati region, USA. Key words: Cambrian, helcionellid, Mollusca, Mackinnonia, Australia, shell microstructure, biomineralization. INTRODUCTION The occurrence of shell microstructure data in molluscs from both the Cambrian (e.g. Runnegar 1985) Fine microstructural detail can be preserved in calcium as well as Ordovician (e.g. Mutvei 1997) potentially phosphate internal moulds and replacements of the allows the inference of broad-scale evolutionary patterns. shells of Cambrian molluscs (Runnegar 1985). While Recent data from the Ordovician suggest that the some common molluscan shell microstructures such as aragonitic shell microstructure nacre was fairly wide- prismatic, crossed-lamellar and foliated calcite occur spread by this time (Vendrasco et al.
    [Show full text]
  • Quantum Theory on Genome Evolution
    Quantum patterns of genome size variation in angiosperms Liaofu Luo1 2 Lirong Zhang1 1 School of Physical Science and Technology, Inner Mongolia University, Hohhot, Inner Mongolia, 010021, P. R. China 2 School of Life Science and Technology, Inner Mongolia University of Science and Technology, Baotou, Inner Mongolia,014010, P. R. China Email to LZ: [email protected] ; LL: [email protected] Abstract The nuclear DNA amount in angiosperms is studied from the eigen-value equation of the genome evolution operator H. The operator H is introduced by physical simulation and it is defined as a function of the genome size N and the derivative with respective to the size. The discontinuity of DNA size distribution and its synergetic occurrence in related angiosperms species are successfully deduced from the solution of the equation. The results agree well with the existing experimental data of Aloe, Clarkia, Nicotiana, Lathyrus, Allium and other genera. It may indicate that the evolutionary constrains on angiosperm genome are essentially of quantum origin. Key words: Genome size; DNA amount; Evolution; Angiosperms; Quantum Introduction DNA amount is relatively constant and tends to be highly characteristic for a species. The nuclear DNA amounts of angiosperm plants were estimated by at least eight different techniques and mainly (over 96%) by flow cytometry and Feulgen microdensitometry. The C-values for more than 6000 angiosperm species were reported till 2011(1). It is found that these C-values are highly variable, differing over 1000-fold. Changes in DNA amount in evolution often appear non-random in amount and distribution (2-4).
    [Show full text]
  • On Two Quantum Approaches to Adaptive Mutations in Bacteria
    On two quantum approaches to adaptive mutations in bacteria. Vasily Ogryzko* INSERM, CNRS UMR 8126, Universite Paris Sud XI Institut Gustave Roussy, Villejuif, France Key words: Adaptive mutations, quantum mechanics, measurement, decoherence, Lamarck [email protected] http://sites.google.com/site/vasilyogryzko/ ABSTRACT approach. The positive role of environmentally induced decoherence (EID) on both steps of the The phenomenon of adaptive mutations has been adaptation process in the framework of the Q-cell attracting attention of biologists for several approach is emphasized. A starving bacterial cell is decades as challenging the basic premise of the proposed to be in an einselected state. The Central Dogma of Molecular Biology. Two intracellular dynamics in this state has a unitary approaches, based on the quantum theoretical character and is proposed to be interpreted as principles (QMAMs - Quantum Models of ‘exponential growth in imaginary time’, Adaptive Mutations) have been proposed in analogously to the commonly considered order to explain this phenomenon. In the present ‘diffusion’ interpretation of the Schroedinger work, they are termed Q-cell and Q-genome equation. Addition of a substrate leads to Wick approaches and are compared using ‘fluctuation rotation and a switch from ‘imaginary time’ trapping’ mechanism as a general framework. reproduction to a ‘real time’ reproduction regime. Notions of R-error and D-error are introduced, Due to the variations at the genomic level (such as and it is argued that the ‘fluctuation trapping base tautomery), the starving cell has to be model’ can be considered as a QMAM only if it represented as a superposition of different employs a correlation between the R- and D- components, all ‘reproducing in imaginary time’.
    [Show full text]
  • New Middle Cambrian Molluscs from the Láncara Formation of the Cantabrian Mountains (North-Western Spain)
    MIDDLE CAMBRIAN MOLLUSCS OF THE CANTABRIAN MOUNTAINS 145 NEW MIDDLE CAMBRIAN MOLLUSCS FROM THE LÁNCARA FORMATION OF THE CANTABRIAN MOUNTAINS (NORTH-WESTERN SPAIN) Thomas WOTTE Geological Institute, Freiberg University of Mining and Technology, Bernhard- von-Cotta street 2, D-09599 Freiberg, Germany. [email protected]. Wotte, T. 2006. New Middle Cambrian molluscs from the Láncara Formation of the Cantabrian Mountains (north- western Spain). [Nuevos moluscos de la Formación Láncara, Cámbrico Medio de la Cordillera Cantábrica (No- roeste de España).] Revista Española de Paleontología, 21 (2), 145-158. ISSN 0213-6937. ABSTRACT An abundant and highly diverse fauna is characteristic for the nodular limestones of the upper member of the Láncara Formation. It consists of echinoderms, trilobites, brachiopods, molluscs, sponge- and chancelloriid re- mains, and other small shelly fossils. Whereas the trilobites of the Láncara Formation are well investigated, in- formation on other faunal groups is clearly underrepresented. In this paper the Middle Cambrian helcionelloid molluscs and hyoliths of the upper member of the Láncara Formation from four sections are described for the fi rst time. The mollusc fauna shows clear affi nities to Siberia, South Australia, Greenland, and China. The fol- lowing taxa were described: Protowenella lancaraensis new species, Mackinnonia cf. rostrata (Zhou & Xiao, 1984), Pelagiella subangulata (Tate, 1892), Conotheca sp., and Microcornus sp. Key words: Molluscs, Helcionellida, Hyolitha, Middle Cambrian, Láncara Formation, Cantabrian Moun- tains, Spain. RESUMEN En las calizas nodulosas del miembro superior de la Formación Láncara se registra una abundante y diversifi - cada fauna; en la que se han encontrado equinodermos, trilobites, braquiópodos, moluscos, esponjas y restos de chancelóridos, y otros pequeños fósiles conchíferos (SSF).
    [Show full text]
  • Shell Microstructures in Early Mollusks
    Vol. XLII(4): 2010 THE FESTIVUS Page 43 SHELL MICROSTRUCTURES IN EARLY MOLLUSKS MICHAEL J. VENDRASCO1*, SUSANNAH M. PORTER1, ARTEM V. KOUCHINSKY2, GUOXIANG LI3, and CHRISTINE Z. FERNANDEZ4 1Institute for Crustal Studies, University of California, Santa Barbara, CA, 93106, USA 2Department of Palaeozoology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden 3LPS, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, P.R. China, 414601 Madris Ave., Norwalk, CA 90650, USA Abstract: Shell microstructures in some of the oldest known mollusk fossils (from the early to middle Cambrian Period; 542 to 510 million years ago) are diverse, strong, and in some cases unusual. We herein review our recent work focused on different aspects of shell microstructures in Cambrian mollusks, briefly summarizing some of the major conclusions from a few of our recent publications and adding some new analysis. Overall, the data suggest that: (1) mollusks rapidly evolved disparate shell microstructures; (2) early mollusks had a complex shell with a different type of shell microstructure in the outer layer than in the inner one; (3) the modern molluscan biomineralization system, with precise control over crystal shapes and arrangements in a mantle cavity bounded by periostracum, was already in place during the Cambrian; (4) shell microstructure data provide a suite of characters useful in phylogenetic analyses of mollusks and mollusk-like Problematica, allowing better determination
    [Show full text]