Carboniferous biostratigraphy of rugose corals

Rugose corals are one of the major fossil groups in shallow-water environments. They played an important role in dividing and correlating Carboniferous strata during the last century, when regional biostratigraphic schemes were established and may be useful for long-distance correlation. Carboniferous rugose corals document two evolutionary events. One is the Tournaisian recovery event, with abundant occurrences of typical Carboniferous rugose corals such as columellate taxa and a significant diversification of large, dissepimented corals. The other is the changeover of rugose coral composition at the mid-Carboniferous boundary, which is represented by the disappearance of many large dissepimented taxa with complex axial structures and the appearance of typical Pennsylvanian taxa characterized by compound rugose taxa. The biostratigraphic scales for rugose corals show a finer temporal resolution in the Mississippian than in the Pennsylvanian, which was probably caused by the Late Paleozoic Ice Age that resulted in glacial-eustatic changes and a lack of continuous Pennsylvanian carbonate strata. The Pennsylvanian rugose corals are totally missing in the Cimmerian Continent. High-resolution biostratigraphy of rugose corals has so far only achieved in few regions for the Mississippian time scale. In most regions, more detailed taxonomic works and precise correlations between different fossil groups are needed.

Early development and coloniality in Oligophylloides from the Devonian of Morocco—Are Heterocorallia Palaeozoic octocorals?

Heterocorals represent an enigmatic group of Palaeozoic corals, known from relatively short time intervals in the Devonian and Carboniferous periods. The major differences between Heterocorallia and other Palaeozoic corals are the lack of an external theca (epitheca), lack of calices and the presence of dichotomously dividing septa-like structures. Heterocoral skeleton was presumably externally covered by the soft tissue and each branch of their skeleton has, until now, been regarded as a corallite–a skeleton of a single polyp. We investigated upper Famennian Oligophylloides from Morocco, focussing on branching processes, wall structure, previously poorly known initial growth stages and the growing tip, described here for the first time. We demonstrate that Oligophylloides shows a unique colony development not known in any group of anthozoans possessing a septate-like architecture and suggest that the previously postulated homology between true septa in hexa- and rugose corals on one hand, and Oligophylloides on the other, must be rejected. Based on the skeleton structure and branching patterns, we postulate, contrary to former ideas, that the stem and branches of heterocorals represent the skeleton of a multi-polyp colonial coral, similar to many extant octocorals. We found numerous potential homologies with octocoral skeletons (notably the Keratoisidinae within the Isididae) and, as a result, we propose the inclusion of the order Heterocorallia within the subclass Octocorallia. This suggestion requires, however, further research on the other taxa of heterocorals. We also propose some changes to the morphological terminology for the Heterocorallia.

First report of Devonian corals from the Bitlis-Pötürge Massif (SE Turkey): a rare occurrence of corals on the northern margin of Gondwana

The Bitlis-Pötürge Massif of SE Turkey is a metamorphic belt separating the Arabian Plate from the Taurides. It includes a non-metamorphic Palaeozoic sequence that contains locally fossiliferous strata. Here is reported for the first time an assemblage of Upper Devonian rugose and tabulate corals from the Meydan Formation, composed of the rugose Frechastraea schafferi (PENECKE), Peneckiella cf. teicherti HILL, Pseudopexiphyllum supradevonicum (PENECKE), and Macgeea desioi VON SCHOUPPÉ, and the tabulate Thamnopora reticulata (DE BLAINVILLE), Alveolites ex. gr. suborbicularis and Scoliopora sp. The rugose corals suggest a Late Frasnian age. The palaeobiogeographic affinities of corals are discussed. The species F. schafferi and the genus Pseudopexiphyllum –so far only reported from Turkey, Iran and Afghanistan– are probably limited to the northern margin of Gondwana and therefore diagnostic for this palaeogeographic area. Until now, the northern margin of Gondwana yielded very few Upper Devonian corals so this occurrence in SE Turkey is particularly important to estimate the relationship between these corals and the ones from the northern margin of the Palaeotethys Ocean.

Labechia carbonaria Smith 1932 in the Early Carboniferous of England; affinity, palaeogeographic position and implications for the geological history of stromatoporoid-type sponges

Stromatoporoid sponges were very abundant during the middle Palaeozoic Era and are thought to disappear at the end of the Devonian Period in the Hangenberg Crisis. However, there are records of organisms with stromatoporoid-type structure in Carboniferous strata, the subject of this study. The Viséan fossil Labechia carbonaria Smith 1932 has been discussed previously in literature and its affinity has not been confirmed. In this study, the type material of L. carbonaria collected from the middle part of the Frizington Limestone Formation (previously called Seventh Limestone), Holkerian Substage, stored in the Natural History Museum (London, UK) and British Geological Survey (Keyworth, UK) was re-examined. The Holkerian Substage, in which L. carbonaria was found, lies between ca 335–339 Ma, and the Frizington Limestone Formation ranges from topmost Arundian to upper Holkerian, so middle Frizington Limestone Formation is likely approximately 337 Ma. L. carbonaria comprises thick long pillars connected by thin curved cyst plates consistent with the structure of the stromatoporoid genus Labechia. However, a common opinion is that L. carbonaria fossils may be mistaken for fragments of rugose corals, but there are problems with assigning it to the Rugosa. In vertical section (VS) L. carbonaria could be mistaken for a transverse section (TS) of a Carboniferous rugose coral. However, in TS L. carbonaria shows the rounded cross sections of stromatoporoid pillars. If it was a coral, septal sheets of the VS of a coral should be seen. For a rugose affinity to still apply, a coral structure would have to be composed of free trabeculae, but these are not known after the middle of the Devonian Period; there are no corals of Early Carboniferous age with the structure of L. carbonaria. Another interpretation, that L. carbonaria is a chaetetid, is discounted because it lacks calicles and is very different in structure from chaetetids. We conclude that L. carbonaria is a stromatoporoid. Because the beginning of the Carboniferous Period was ca 359 Ma, stromatoporoids thus occur approximately 22 million years after their purported disappearance at the end-Devonian Hangenberg Crisis. L. carbonaria, together with other rare occurrences in Carboniferous strata of stromatoporoid-form sponges Newellia mira (Newell) in USA, and uncertain taxa Komia Korde and Palaeoaplysina Krottow that have been attributed to stromatoporoids by some authors, supports some published views that end-Devonian stromatoporoid extinction may not have been as final as is traditionally interpreted. Thus Mesozoic stromatoporoids may represent resurgence of sponge lineages that survived the late Palaeozoic, perhaps in uncalcified form. Palaeogeographically, during the Early Carboniferous, the UK was positioned in low latitudes and in a central location of global distribution of reefal buildups during the late Palaeozoic continental assembly towards Pangaea. Thus it is curious that L. carbonaria is found in only one place; future search may determine its true palaeographic distribution, with potential reconsideration of the extinction of stromatoporoids at the end of the Devonian Period.

SYMBIOSIS OF RUGOSE CORALS WITH THE CYSTOPORATE BRYOZOAN FISTULIPORA PRZHIDOLENSIS IN THE PRIDOLI (LATEST SILURIAN) OF SAAREMAA, ESTONIA

ABSTRACT In the Silurian, the most common hosts of endobiotic rugose corals were stromatoporoids followed by tabulate corals. Here we describe the relationship between rugose corals and a bryozoan. Solitary rugosans and the cystoporate bryozoan Fistulipora przhidolensis Kopajevich, 1990 formed a symbiotic association in the late Silurian (Pridoli) of Saaremaa, Estonia. The syn vivo nature of the association is indicated by complete intergrowth of both organisms and the perpendicular orientation of the rugosans to the bryozoan growth surface. There are one to seven endobiotic rugosans per bryozoan colony. This is the first detailed study of coral-bryozoan symbiosis from the Silurian; all previous reports describe Late Ordovician, Devonian, or Cenozoic material. The lack of malformations and decrease in the size of bryozoan zooids near the rugosans suggest there were no strong negative effects of the rugosans on the bryozoan. The rugosans likely benefited from their association with the bryozoan, which served as an anchor to stabilize them in hydrodynamically active waters, and the bryozoan may have benefited by protection against some types of predators. The associations described here were most likely mutualistic.