Jean Lafuste

Tabulaconus handfield; microstructure and its implication in the taxonomy of primitive corals

Numerous specimens of Tabulaconus Handfield, 1969, have been collected in carbonate buildups within the Adams Argillite (Early Cambrian, Tatonduk area, Alaska). The wall structure of this form has been investigated, along with contemporaneous archaeocyaths and algae, through the use of polished ultra-thin sections (2–3 μm thick) and scanning electron microscopy. The results of this microstructural comparison indicate that despite diagenetic alteration Tabulaconus has a skeleton that is unlike any presently known and is quite distinct from associated algae or archaeocyaths. It is more elaborate than that found in the archaeocyaths but has not reached the stage of complexity seen in the primitive coral Cothonion Jell and Jell, 1976. The presence of some elongated units may represent an initial step towards the fibrous skeleton typical of Paleozoic corals. This study shows that even though diagenesis alters the original microstructure of calcareous skeletons, the resultant fabrics and detailed structures can be useful in systematic descriptions. Tabulaconus is removed from the Gastroconidae Kordae due to the presence of rudimentary septa and constitution of the tabularium. A number of species assigned to the genus Bacatocyathus Vologdin and included within the Archaeocyatha appear to be examples of Tabulaconus or very close relatives. An emended description of Tabulaconus kordae , the type species, is proposed.

The oldest tabulate coral and the associated archaeocyatha, Lower Cambrian, Flinders Ranges, South Australia

Abstract The oldest known tabulate, Flindersipora bowmani Lafuste gen. et sp. nov. from the Flinders Ranges of South Australia, is described for the first time. The new genus presents all morphological and structural characteristics of Tabulate: cerioid shape, septal ridges, tabulae, wall pores. Its microstructure is nevertheless new, formed by “platelets”. Specimens have been found associated with archaeocyaths and calcified cyanobacteria in Lower Cambrian shelf margin buildups in the Oraparinna Shale and Moorowie Formation, in two different localities: Ten Miles Creek, where they are associated with solitary archaeocyaths, and Moorowie Mine, where they built complex bioconstructions associated with colonial archaeocyaths. The archaeocyaths, comprising 11 species, indicate a middle Botomian age. One species Robertocyathus brenti Debrenne is new. The buildups were among the last to flourish prior to widespread regression in the Early Cambrian in South Australia. With this discovery, the present opinions on the phylogeny of Tabulate Corals must be modified. In comparison with some Cambrian or even Ordovician forms which have been supposed to have affinities with corals, Flindersipora has a less rudimentary morphology and could not be said more primitive than these previously known genera. Because of its advanced favositid architectural type Flindersipora reinforce the idea that the origin of Tabulate is very ancient and must be looked for in the Precambrian.

Attribution de «Michelinia compressa Michelin, 1847 au genre Yavorskia Fomitchev (Tabulé, Tournaisien)

Resume Une coupe longitudinale effectuee dans le type de Michelinia compressa Michelin montre que cette espece appartient au genre Yavorskia Fomitchev .

Précisions sur la structure et la microstructure du genreRoemeria Milne-Edwards & Haime 1851 (Tabulata, Dévonien moyen d’Allemagne et de Belgique)

Three Middle Devonian tabulate coral species assigned to the genusRoemeria Milne-Edwards & Haime 1851 are described:R. infundibulifera (Goldfuss 1829), the type species of the genus, andR. minor SCHLÜTER 1885, both from the Rheinisches Schiefergebirge, and a new species,R. cubiniensis, from the Couvin area of Belgium. Their external and internal characters and microstructures are described in detail. The dominant morphological features they have in common are cerioid and locally fasciculate corallites and tabulae with an infundibuliform profile. The microstructure of the corallite walls is characterized by an hitherto undescribed association of an internal fibrous zone and a peripheral lamellar zone flanking a median plate made of small granules and larger elements of stellate form. The only micro-structural variation between the three species lies in the proportions of these components. Kurzfassung: Drei mittel-devonische tabulate Korallen-Arten werden zur GattungRoemeria Milne-Edwards & Haime 1851 gestellt und beschrieben: die Typus-ArtenR. infundibulifera (Goldfuss 1829) sowieR. minor SchlÜter 1885, beide aus dem Rheinischen Schiefergebirge, und eine neue Art,R. cubiniensis, aus der Umgebung von Couvin in Belgien. Äußere und innere gemeinsame Merkmale sind cerioide und nur stellenweise bündeiförmige Koralliten mit einem infundibuliformen Profil der Tabulae im Längsschnitt. Die MikroStruktur der Koralliten-Wände ist durch die bisher nicht beschriebene Verbindung einer internen fibrösen Zone mit einer peripheren Lamellenschicht gekennzeichnet, die um eine Median-Lamelle aus kleinen und großen Granulae mit Stern-Profil angeordnet sind. Nur das Größen-Verhältnis dieser Struktur-Elemente ist bei den drei beschriebenen Arten verschieden.