Fernández López, Sixto Rafael

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First Name
Sixto Rafael
Last Name
Fernández López
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Geológicas
Geodinámica, Estratigrafía y Paleontología
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Now showing 1 - 10 of 21
  • Publication
    Postulates of the evolutionary taphonomy
    (Instituto Geológico Minero y Metalúrgico, 2013) Fernández López, Sixto Rafael; Chacaltana, C.; Tejada, L.M.; Morales, M.C.
  • Publication
    First Circum-Pacific Record of Dimorphinites (Ammonoidea, Upper Bajocian) in the Precordillera of Northern Chile
    (China University of Geosciences (Beijing); Peking University, 2010) Fernández López, Sixto Rafael; Chong Díaz, G.B.
  • Publication
    How Can Taphonomy Be Defined in the XXI Century?
    (The Paleontological Society., 2011) Domínguez Rodrigo, Manuel; Fernández López, Sixto Rafael; Alcalá, Luis
    Taphonomy, as a branch of learning and a research area, has undergone a tremendous growth in the past few decades. It has extended its application from palaeontology to other disciplines, it has broadened its referential scope and has incorporated humans as taphonomic agents. This has affected the way taphonomy is perceived by its practitioners and requires a modification of its definition, following a process that is common in most evolving natural science disciplines.
  • Publication
    Dimorphism and evolution of Albarracinites (Ammonoidea, Lower Bajocian) from the Iberian Range (Spain)
    (The Trustees of the Natural History Museum,, 2013-12) Fernández López, Sixto Rafael
    Several tens of specimens of Lower Bajocian Albarracinites (type species A. albarraciniensis Fernandez-Lopez, 1985), including microconchs and macroconchs from the Iberian Range, have been studied. This ammonite genus ranges in the Iberian Range from at least the Ovale Zone to the uppermost Laeviuscula Zone of the Lower Bajocian (Middle Jurassic). The macroconch counterpart is thought to be a group of stephanoceratids previously attributed to Mollistephanus, Riccardiceras and other new forms described in this paper. Two chronologically successive species of Albarracinites have been identified: A. albarraciniensis and A. submediterraneus sp. nov. The evolution of the Albarracinites lineage represents a hypermorphic peramorphocline starting from depressed, small and slender serpenticones of A. westermanni, to larger planorbicones with more cadiconic phragmocones and body chamber of subcircular cross section belonging to A. submediterraneus sp. nov., through A. albarraciniensis Fernandez-Lopez. In contrast, Mollistephanus planulatus (Buckman), M. cockroadensis Chandler & Dietze and M. mollis Buckman represent a peramorphocline by acceleration, producing adults of similar size but more compressed and with increasing ontogenic variation of shell ornament. Albarracinites and Mollistephanus subsequently developed two opposite peramorphoclines or gradational series of morphological changes undergoing greater development and ontogenic variation. These two genera show diverse palaeobiogeographical distributions too. Albarracinites is rarely recorded in the Mediterranean and Submediterranean from the Discites to the Laeviuscula Zone, whereas Mollistephanus is more common in north-western Europe and other biochoremas of the western Tethys from the Discites Zone to the Sauzei Zone. Albarracinites seems to be the earliest stephanoceratid lineage in western Tethys, branching off from the otoitid Riccardiceras by proterogenetic change and resulting in paedomorphosis at the Aalenian/Bajocian boundary.
  • Publication
    Bajocian Lissoceratinae (Haploceratoidea, Ammonitida) from the Mediterranean-Caucasian Subrealm
    (Università degli Studi di Milano, 2019-03) Pavia, Giulio; Fernández López, Sixto Rafael
    A revision of the Bajocian Lissoceratinae is presented. The study of a huge quantity of lissoceratins from different sites of the Western Tethys (Northwest European, Sub-Mediterranean and Mediterranean bioprovinces) within the Tethys-Panthalassa Realm provided data useful to implement the systematics of these almost neglected, never deeply analysed ammonites. Two genera, Lissoceras Bayle and Semilissoceras n. gen., are described with 16 species, among which 8 (four dimorphic, three macroconchiate and one microconchiate) new species: L. submediterraneum, L. maizetense, L. ovale, L. sturanii, L. maerteni, S. ellipticum, S. turgidulum and S. costellatum. The neotype of L. oolithicum is established. The microconchiate genus Microlissoceras is regarded as the junior synonym of the macroconchiate Lissoceras. Taxa are discussed according to four groups that gather taxa sharing common morpho-structural features. They roughly relate to successive biochronostratigraphical intervals within the Bajocian Stage and are headed by species largely known in literature: S. semicostulatum (Buckman) with suboval to compressed whorl section and rectiradiate ribs on the outer half flank; L. oolithicum (d’Orbigny) with subtriangular to ovate whorl section, large and depressed ventral saddle, large suspensive lobe; L. haugi Sturani with ovate to globular whorl section, narrow lobe E and suspensive lobe; and L. psilodiscus (Schloenbach) with highly compressed whorl section, high ventral saddle and narrow lobe E. The phyletic relation of Lissoceras and Semilissoceras to the Aalenian-Bajocian Bradfordia-group is discussed, regarding Semilissoceras as the known stem-taxon on which the subfamily Lissoceratinae bases.
  • Publication
    Invertebrate Palaeontology and Sequence Stratigraphy: complementary methods and evidence to explain the geological record
    (Universidade Nova de Lisboa. Faculdade de Ciências e Tecnologia, 2013) Fernández López, Sixto Rafael; Sha, Jingeng
    The fossil record and the stratigraphic record are two components of the geological record different in nature, and they can be separately interpreted and tested in many cases of Invertebrate Palaeontology. Abundance, diversity and stratigraphic persistence are outstanding features of the fossil invertebrates. Therefore, the complementarity (as the capacity of two contrasted theories together to explain a body of phenomena, although each separately accounts for only some aspects) or the consilience (as the fact or condition of being inferred from different phenomena) between Palaeontology and Sequence Stratigraphy through the study of fossil invertebrates is specially useful for the interpretation of the geological record and the palaeoenvironmental changes.
  • Publication
    New species of Franchia and Protozigzagiceras (Ammonoidea, Middle Jurassic): The phyletic origin of Zigzagiceratinae
    (Blackwell Publishing Ltd, 2013) Fernández López, Sixto Rafael; Pavia, Giulio
    Three genera and seven species belonging to the subfamily Zigzagiceratinae (family Perisphinctidae) are described from the Lower Bathonian of France and Saudi Arabia. Intraspecific dimorphism is recognized. A revision of the genus Franchia proposed by Sturani (1967), based on the syntypes and new specimens from south-east France, is presented. Franchia arkelli Sturani, Franchia subalpina sp. nov., Protozigzagiceras torrensi (Sturani), Protozigzagiceras tethycum sp. nov., Protozigzagiceras flexum sp. nov. and Protozigzagiceras densum sp. nov. are described from the Digne– Castellane region of south-east France. Megazigzagiceras subarabicum, gen. et sp. nov. is described from the Dharma region of Saudi Arabia. The successive Early Bathonian species of Franchia and Protozigzagiceras herein identified in West Tethyan areas, as members of the Mediterranean–Caucasian Subrealm, formed lasting separate peramorphoclines characterized by increasing hydrodynamic coiling of the shell. In contrast, rapid proterogenesis originated and diversified the earliest Bathonian zigzagiceratin lineages, giving paedomorphic members, commonly neotenic and more scarcely progenetic. Procerites–Siemiradzkia seems to be the oldest zigzagiceratin member in the French Subalpine, Iberian and Lusitanian basins, branched off by paedomorphosis from leptosphinctins at the Bajocian–Bathonian transition. The Mediterranean–Caucasian genera Franchia, Zigzagiceras, Zigzagites and Wagnericeras branched from successive species of Protozigzagiceras, in turn, a direct derivative of Procerites. The oldest lineages of the clade Zigzagiceratinae evolved by iterative, rapid, paedomorphic changes and additional, lasting, peramorphic modifications during the Early Bathonian.
  • Publication
    Pseudoteloceras, a new stephanoceratid genus (Ammonitida) of the lower Humphriesianum Zone (lower Bajocian, Middle Jurassic) from western Tethys
    (Elsevier, 2016-05) Pavia, Giulio; Fernández López, Sixto Rafael
    The new dimorphic genus Pseudoteloceras (type-species: P. crosillense gen. et sp. nov.) is defined within the subfamily Stephanoceratinae. It constitutes the terminal step of an early Bajocian phyletic trend that produces Teloceras-like morphologies throughout the lower Humphriesianum Zone of the western Mediterranean-Caucasian Subrealm, at an older chronological interval and with morpho-structural features that stand apart from those of the best known genus Teloceras of the uppermost Humphriesianum and lower Niortense zones at the early/late Bajocian transition. Three new species are described: P. croisillense, P. maerteni and P. boursicoti. Their biochronostratigraphical ranges are confirmed by the distribution in expanded sections of the Subalpine Basin in Submediterranean Province (Digne area) and the taphonomic analysis of fossil assemblages from the condensed sections of the “Oolithe ferrugineuse de Bayeux” Formation in Calvados, North West European Province. The biochronostratigraphical range of Pseudoteloceras gen. nov. is limited to the Romani Subzone, lower Humphriesianum Zone. P. crosillense gen. et sp. nov. marks a well-defined biohorizon of the upper Romani Subzone in the Digne stratigraphical successions. The extreme degree of the cadiconic morphology in the inner whorls of P. boursicoti gen. et sp. nov., and the biostratigraphical gap separating the first appearance of the genus Teloceras in the upper Humphriesianum Zone, support its erection as a new taxon Pseudoteloceras gen. nov. A fourth species, Pseudoteloceras geometricum (Maubeuge), is interpreted as the earliest species of this phyletic lineage, derived from Stemmatoceras and widely distributed through western Tethys in the lower Humphriesianum Zone.
  • Publication
    Parkinsoniids and garantianids (Late Bajocian Ammonoidea) as guide fossils and biostratigraphic indices
    (Freunde der Würzburger Geowissenschaften e.V., 2014) Pavia, Giulio; Fernández López, Sixto Rafael