THE HERCYNIAN ARBURESE TECTONIC UNIT OF SW SARDINIA. NEW STRATIGRAPHIC AND STRUCTURAL DATA

New structural and biostratigraphic data, mainly based on conodonts, permit the recognition of three different sub-units within the Hercynian Arburese Tectonic Unit of SW Sardinia, which are here described. Some stages and conodont biozones of Silurian-Early Devonian age are reported for the first time in Sardinia

First documentation of the Polygnathoides siluricus conodont Zone (Ludfordian) in South America (Argentina) and the stratigraphic significance of the younger species of Kockelella (Conodonta)

The coquinoid beds from the middle part of the Los Espejos Formation at the Poblete creek section (Talacasto Creek) yielded abundant conodonts. The genus Kockelella (Walliser) represents the most relevant biostratigraphical genus in this conodont fauna. The co-occurrence of Kockelella maenniki Serpagli and Corradini, Kockelella variabilis ichnusae Serpagli and Corradini, K. variabilis Walliser, Kockelella ortus sardoa (Serpagli & Corradini), and Kockelella ortus absidata (Barrick & Klapper) allow us to record for the first time the Polygnathoides siluricus Zone in South America, which suggests the Ludfordian Stage (late Ludlow). We also propose an accurate correlation of the Los Espejos Formation with the lower Ludfordian deposits from the Carnic Alps, Sardinia, Morocco, Czech Republic, Gotland, and North America.Fil: Gomez, Maria Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Mestre, Ana Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Garcias Paez, Yanina Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Corradini, Carlo. Università degli Studi di Cagliari; Itali

A new icriodontid conodont cluster with specific mesowear supports an alternative apparatus motion model for Icriodontidae

Increasing numbers of conodont discoveries with soft tissue preservation, natural assemblages and fused clusters of the hard tissue have strengthened the hypothesis regarding the function and mechanism of the conodont feeding apparatus. Exceptional fossil preservation serves as a solid basis for modern reconstructions of the conodont apparatus illustrating the complex interplay of the single apparatus elements. Reliable published models concern the ozarkodinid apparatus of Pennsylvanian and Early Triassic conodonts. Recognition of microwear and mammal-like occlusion, especially of platform elements belonging to individuals of the genus Idiognathodus, allows rotational closure to be interpreted as the crushing mechanism of ozarkodinid platform (P1) elements. Here we describe a new icriodontid conodont cluster of Caudicriodus woschmidti that consists of one pair of icriodontan (I) and 10 pairs of coniform (C1\ue2\u80\u935) elements, with I elements being preserved in interlocking position. The special kind of element arrangement within the fused cluster provides new insights into icriodontid apparatus reconstruction and notation of elements. However, orientation of coniform elements is limited to a certain degree by possible preservational bias. Four possible apparatus models are introduced and discussed. Recognition of specific wear on denticle tips of one of the icriodontan elements forms the basis for an alternative hypothesis of apparatus motion. Analysis of tip wear suggests a horizontal, slightly elliptical motion of opposed, antagonistically operating I elements. This is supported by similar tip wear from much better preserved, but isolated, elements of Middle Devonian icriodontids. More detailed interpretation of the masticatory movement will allow enhanced understanding of anatomical specifications, diet and palaeobiology of different euconodont groups

First record of the ichnofossil Atollites from the Late Cretaceous of the Northern Apennines, Italy

A new radial trace fossil, Atollites italicum ichnosp. nov., is reported from Upper Cretaceous sediments of the Northern Apennines (Italy). It is made up of several cylinder−club systems, which are interpreted as radiating in a possible faint spiral pattern from a central shaft. The pre−diagenetic reconstruction of the Atollites structure is attempted for the first time. The trace fossil may be attributed to small crustaceans or, less probably, it represents a feeding burrow of other deposit feeders

Functional morphology of the cap-like apparatus in autozooids of a Paleozoic trepostome bryozoan

Functional morphology in Ordovician bryozoaA membranous, cap‐like structure was discovered in the bryozoan genus Hallopora from upper Ordovician siltstones from Sardinia. The structure is interpreted to be analogous to the perimetrical attachment organ and to the part of the membranous sac sustaining the sphincter muscle in Recent cyclostomes. The progressive mineralization of the cap‐like apparatus occurred in later ontogenetic stages of the colony in order to have the function of a terminal diaphragm. This diaphragm is related to a particular degeneration—regeneration cycle very similar to the cyclic growth patterns (intracolony overgrowths) of some post‐Palaeozoic cyclostomes. After this phase the colony seems to end its life cycle. Copyright © 1987, Wiley Blackwell. All rights reserve

A Silurian conodont zonation from late Llandovery to end Pridoli in Sardinia

The standard Late Llandovery - Top Pridoli conodont zonation between the top of the celloni Zone and the latest Pridoli detorta Zone is revised on the basis of data from the Silurian System of Sardinia. Fifteen biointervals have been recognized; among them, one zone is here newly named (Oz. exc. hamata) and three more zones (K. crassa, K. v. variabilis interval Zone and Pe. latialata), proposed and sporadically used in some previous biozonations, are reintroduced. The scheme provided for Sardinia fits well in other part of the world, like the Cellon section

Bimineralic (calcareous and phosphatic) skeleton in Late Ordovician Bryozoa from Sardinia: Geological implications.

The study of Palaeozoic Bryozoa from the Upper Ordovician of Sardinia was carried out by integrating the traditional thin section description with the SEM observation of single zooecia or zoarial remnants, isolated by acid acetic technique. This technique was made possible by the presence of a bimineralic (calcareous and phosphatic) skeleton,which is interpreted as the result of the mineralization of the membranous part of the cryptocyst originally very rich in phosphorus. The frequent records of phosphatic bodies in Bryozoa lead us to hypothesize the possibility that some Bryozoa secrete,at least in the Palaeozoic, a phosphatic skeleton in response to particular environmental conditions. The deposition of calcium phosphate occurred in the zooecial cavity owing to the change in chemical conditions between the regeneration and degeneration phases