Decline in diversity of early Palaeozoic loosely coiled gastropod protoconchs

Quantitative data on molluscan larval conch fossil assemblages of ages ranging from the Ordovician (Argentina and the Baltic region), through Silurian (Austria), Devonian (Poland) to Carboniferous (Texas) supplement knowledge of early planktonic gastropods communities transformations. They show that larval shells of the bilaterally symmetrical bellerophontids and dextrally coiled gastropods with a hook-like straight apical portion of the first whorl initially dominated. Their relative frequency, as well as that of the sinistrally coiled ‘paragastropods’, diminished during the Ordovician and Silurian to virtually disappear in the Late Devonian and Early Carboniferous. Already during the Ordovician, diversity of larvae with gently loosely coiled first whorl increased, to be replaced then with more and more tightly coiled forms. Both the aperture constrictions and mortality peaks, probably connected with hatching and metamorphosis, indicate that the Ordovician protoconchs with hook-like first coil represent both the stage of an embryo developing within the egg envelope and a planktonic larva. The similarity of the straight apex to larval conchs of hyoliths and advanced thecosome pteropods is superficial, as these were not homologous stages in early development.     

Dictyodora and associated trace fossils from the Palaeozoic of Thuringia

Dictyodora occurs in the Hauptquarzit (Late Ordovician; D. zimmermanni) and Bordenschiefer (Early Carboniferous; D. liebeana) of Thuringia, East Germany. It is absent in the Early Devonian Nereitenquarzit, and analysis of the trace fossil assemblages points to environmental partitioning within the ‘deep-sea’Nereites Association. The Carboniferous Dictyodora was much larger than the Early Palaeozoic forms and had a long respiratory (?) wall organ. This may have been an adaptation to feeding deeper in anoxic sediments, and the animal developed large ‘parapodia’ to effect its progression through the sediment.     

Population dynamics of the Late Devonian conodont Alternognathus calibrated in days

Abstract

Alternognathus is a cavusgnathid conodont believed to be a relative and possible ancestor of the Siphonodella lineage, which is of crucial importance to the biostratigraphy of the Devonian–Carboniferous transition, as well as the Early Carboniferous Clydagnathus, with the most completely known soft tissue anatomy among conodonts. Specimens of Alternognathus from the Kowala quarry in central Poland have their basal cavities lacking any mineralised basal body tissue, exposing rhythmic growth increments of probably daily nature. This enables calibration of ontogeny and population dynamics of Alternognathus in absolute time units and to estimate the correspondence between data derived from isolated oral apparatus elements and the animal body size. The peak of mortality, probably resulting from predation, occurred at 18–28 days of the Alternognathus oral apparatus element secretion and the inferred whole animal length of about 1.6–2.9 cm. Based on analogy with present-day fish, the actual beginning of individual life presumably preceded the initiation of the mineral tissue secretion for about 8 days. This makes the dominant life cycle close to the lunar month length and suggests analogy to cyclic mortality of modern tropical organisms due to full moon light influence on their daily vertical migration.     

Devonian conodont biogeography: Quantitative analysis of provinciality

Cluster analysis of conodont faunas from each of 17 Lower‐lower Upper Devonian zones and subzones (data as reported by Klapper and Johnson, 1980) reveal changing patterns of provinciality.

Provinciality, expressed by a differentiation into western Laurussian and proto‐Tethyan biogeographic regions, is moderate in the lower Lochkovian but is low or absent in the upper Lochkovian‐lower Pragian. Provincialism returns in the Pragian and reaches its maximum development during the Emsian. Most Australian faunas are distinct from those of western Laurussia and the proto‐Tethys. Conodont faunas from suspect terranes of western North America display no unusual biogeographic affinities. Provincialism declines during the Eifelian and is only weakly developed in Givetian‐lower Frasnian faunas.

Changing global sea level during the Devonian may explain the development of Devonian conodont provinciality. As proposed by Klapper and Johnson (1980), low provinciality is associated with low stands of sea level. Endemic faunas develop in isolated epeiric seas during intermediate stages of sea level rise. High stands of sea level ultimately drown barriers to faunal exchange and prompt a return to low provinciality conditions.     

Early Cretaceous record of microboring organisms in skeletons of growing corals

Ko?odziej, B., Golubic, S., Bucur, I.I., Radtke, G. & Tribollet, A. 2011: Early Cretaceous record of microboring organisms in skeletons of growing corals. Lethaia, Vol. 45, pp. 34–45. A spectacularly preserved assemblage of microbial euendoliths, penetrating into skeletons of growing scleractinian corals, has been recognized in Early Aptian (Early Cretaceous) reef limestone of the Rar?u Mountains (East Carpathians, NE Romania). Microboring euendolithic filaments were found in five coral colonies of the suborder Microsolenina. They remained in part well‐preserved, often impregnated with iron oxides, which made them visible even in strongly recrystallized parts of coral skeletons. Filaments of a wide range of sizes (2–40 μm in diameter) were concentrated within medium parts of coral septa, oriented along the septa in the direction of the coral growth. The larger filaments were tubular, occurring in bundles and branched into finer, often tapering branches. Their behaviour and organization were quite similar to the modern euendolithic siphonalean chlorophyte Ostreobium. Filament diameters exceeded those reported for the modern species, but covered a similarly wide size range. Narrower frequently branching filaments, 4–8 μm in diameter, resemble distal branching patterns of modern Ostreobium quekettii. Some very thin filaments (ca. 1–2 μm) observed within skeleton or inside the large tubular filaments, sometimes associated with globular swellings, may represent euendolithic fungi. The recrystallization of coral skeleton had limited effect on preservation of euendoliths due to their impregnation with iron oxides; microbial euendoliths were subjected to different taphonomic changes. □Chlorophytes, Early Cretaceous, fungi, microbial euendoliths, Romania, scleractinian corals.     

Revised conodont stratigraphy of the Cellon section (Silurian,Carnic Alps)

The Cellon section, located in the Carnic Alps, is a reference section for the Silurian of the world. The conodont association of the section is revised according to the most recent taxonomy and the biostratigraphy updated in the basis of the recently published zonation schemes. Seventy taxa (species and sub‐species) belonging to 23 genera have been identified, allowing the discrimination of 15 biozones from the upper Llandovery to the end of the P?ídolí . However, some of the uppermost Llandovery and Wenlock biozones, corresponding to black shale intervals, have not been documented.     

Predation on bellerophontiform molluscs in the Palaeozoic

Shell repair assumed to result from failed predation is documented in 66 specimens of Ordovician-Carboniferous bellerophontiform tergomyan and gastropod molluscs to examine the relationship between the distribution and appearance of injuries, shell morphology and the internal anatomy of the molluscs, as well as the attack strategies of the presumed predators. Furthermore, the distribution of repaired injuries from failed attacks along the apertural margin as a reflection of the nature of the margin and emarginations is investigated. Bellerophontiform molluscs are ideal for this study because of their distinctive isostrophic morphology and the possibility to directly compare broad and narrow conchs with either deep or shallow medial emarginations. The results show that taxa with a deep medial emargination in the form of a slit have significantly more medial injuries than lateral ones. Near-equal frequencies of lateral and medial injuries in specimens with a shallow emargination (slit or sinus) suggest random distribution. Shell form (narrow or broad) does not exert overall control on the distribution of injuries except, perhaps, in some broad explanate shells with an insignificant medial emargination. While this suggests that it is the type of medial emargination that governs distribution of injuries in these forms, it is not clear if this is a result of passive selection due to structural geometry or preferential targeting by predators (i.e. site-specific mode of attack). Predation strategies on bellerophontiform molluscs thus seem to be dependent on the morphological features of the shells rather than their interpretation as tergomyan or gastropod.     

Appearance and evolution of marine benthic communities in the Early Palaeozoic

The development of marine benthic communities in the Early Palaeozoic occurred mainly in the shallow water epicontinental seas. It included those stages of the Cambrian and Ordovician evolutionary radiations that were dominated by a high rate of morphogenesis, when new food and territory resources were not limited. This provided many opportunities for coadaptation of emerging organisms. At the time of the Cambrian radiation, the body plans of all animals were formed, while in the Ordovician, the maximum rank of emerging taxa did not exceed the level of class. The beginning of each radiation was explosive. Vendian benthic communities developed in cold seas and in the shallowest areas of warm seas, where organic matter from the surface layers was available at the bottom because of the absence of a thermocline. The Cambrian radiation began with the appearance of pelagic suspension feeders, because of which much of the primary production could penetrate the thermocline and settle at the bottom. This allowed the occupation of warmer seas and greater depths. At the same time, the productivity of the pelagic region sharply increased because of the emergence of positive feedback between the producers and consumers in the water, leading to increased water transparency and elongation of trophic chains. Arthropods, the first suspension feeders, were the launch group of the Cambrian radiation. Cambrian benthic suspension feeders could seize only the smallest particles, mostly bacteria, and dissolved organic matter. This food resource was contained in the thin bottom water layer. Therefore, the food grasping structures of all the Cambrian suspension feeders were near the bottom, without forming tiers. The Ordovician evolutionary radiation began with the launch of the Pelmatozoan echinoderms, which were the first benthic suspension feeders to begin feeding on plankton. The exploitation of this resource led to the creation of a 1-m tier above the bottom and an increase in their calcite productivity. Positive feedback emerged between the grounds and the community of its inhabitants and considerably changed the composition and diversity of grounds, which sharply increased the diversity of benthos. The appearance of positive feedback between different components of ecosystems resulted in explosive evolution in both the Cambrian and Ordovician.     

New conodont species from the Kasimovian Stage (Upper Carboniferous) of Moscow and Moscow Basin

Three new conodont species, Streptognathodus neverovensis, S. isakovae, and Idiognathodus mestsherensis, which are widespread in the Kasimovian Stage of central Russia, are described.     

Typostrophism in Palaeozoic Ammonoids?

The anti-Darwinian “Typostrophe Theory” of O.H.Schindewolf can be put to the test by revisiting the ammonoid examples on which this macroevolutionary model was founded. It is shown that none of the three theoretical elements saltationism, internalism, and cyclism can be supported by empirical data obtained from ammonoid research. Putative saltations (“Typogenesis”) were feigned because of the lack of knowledge of intermediate forms. Internalistic and orthogenetic development (“Typostasis”) can only be favoured by neglecting possible functions of morphological characters. Preprogrammed extinction of “degenerated” clades (“Typolysis”) is unlikely when ruling out anthropocentric views regarding ammonoid morphology. In terms of evolution of Palaeozoic ammonoids, there is no basis for the preference of the “Typostrophe Theory” or some of its composing elements, including the “Type Concept” and “Proterogenesis”, over the Darwinian evolutionary model and the Modern Synthesis.      

Disentangling allometry and response to Kellwasser anoxic events in the Late Devonian conodont genus Ancyrodella

Is the ability to respond to minor perturbations a key to survival to major crisis? This idea was supported by previous studies on Late Devonian conodonts. Genera surviving the Frasnian/Famennian (F/F) crisis, at the end of the Upper Kellwasser anoxic event, had shown a response to a similar but minor event, the Lower Kellwasser (LKW). In contrast, the genus Ancyrodella went extinct at the F/F crisis. This study aims to assess whether this extinction was associated with the absence of response to the minor LKW event. For this purpose, the shape of the P1 platform elements of the conodont Ancyrodella curvata was quantified based on their 2‐D outlines. Conodonts were extracted from two outcrops documenting the Late Devonian Kellwasser events, Coumiac (France) and Mrirt (Morocco). Ancyrodella curvata is characterized by a marked allometric growth that may blur any other source of shape difference, like response to the LKW. Hence, a multivariate method was developed to disentangle size‐free from size‐related shape variations. No coherent temporal size variations emerged from the analysis, but allometry occurring along the growth of the element indeed appeared as the prevailing source of shape variation. By isolating size‐free variations, however, we were able to evidence a morphometric response of A. curvata to the LKW independent from the allometric pattern. Hence, the extinction of A. curvata at the F/F crisis cannot be attributed to an absence of response to minor events. The amount of shape change involved in the LKW shift is, however, of minor importance in comparison with the shape variation due to allometric growth. Alternate hypotheses have been further investigated. Ancyrodella curvata appears as a rare species in the assemblages, and its distribution worldwide suggests a rather specialist taxon. Considering survivorship curves (i.e. frequency distribution of the conodont as a function of its size) A. curvata was characterized by low and constant mortality rate. This may be a clue for a long growth and progressive investment in the reproduction. These arguments support the view that A. curvata was a rather specialist, rare and ‘K‐selected’ taxon. All these factors may not be exclusive and their unfavourable conjunction might have been the key to the extinction of A. curvata.     

Systematic distribution of bioluminescence in living organisms

A list of the genera of living organisms known or believed to contain luminous species is provided in the Appendix, in a systematic context. The constraints on the accuracy of such a list and some aspects of the apparent distribution of bioluminescence are discussed.     

Cranial anatomy of ophiderpetontid aïstopods: Palaeozoic limbless amphibians

Oestocephalus , an ophiderpetontid from the Middle Pennsylvanian of both Europe and North America provides the best known basis for evaluating the relationships of the aïstopods. All aïstopods are united by the unique manner of attachment of the skull and the first cervical in which the articulating surface of the occiput is formed by the narrow circular rim of a notochordal pit. As in other aïstopods (but in contrast with all other early tetrapods), the otic-occipital portion of the braincase is ossified as a single element. The palatoquadrate ossification extends from the orbit to the back of the area of jaw articulation. These two characters may be retained from the osteolepiform sarcopterygians. Few, if any, unique derived characters unite aïstopods with other early tetrapods. Their phylogenetic position remains enigmatic.     

Controls on migration of conodont fauna in peripheral oceanic areas. An example from the Middle Triassic of the Northern Peri-Tethys

Middle Triassic conodont assemblages in the semi-closed Peri-Tethyan Germanic Basin comprise endemic forms, which evolved within the basin, and immigrants from the Tethys Ocean. Migration from the Tethys proceeded diachronously through three tectonically predisposed pathways (gates) and was controlled by relative sealevel changes recorded in depositional sequences of the Muschelkalk. In the Early and Middle Anisian predominant were the forms that originated in the Eastern Tethys and in southern basins of the Western Tethys. They migrated through the East Carpathian Gate and Silesian-Moravian Gate. In the late Anisian and early Ladinian forms from the Western Tethyan basins prevailed; their migration pathway led through the Western and East Carpathian Gates. The latter gate was active only at the turn of Illyrian and Fassanian. Episodes of migration of the Tethyan forms and dispersal of conodont fauna throughout the German Basin coincide with the transgressive or highstand phases of a particular depositional sequence (as defined by Szulc, 1999). The most significant proportion of the Tethyan species appears to correlate with the maximum flooding surface of the A₃ sequence, (Lower Muschelkalk) later they decrease in diversity. In the Upper Muschelkalk the most numerous Tethyan species correspond to the transgressive phase of the L₁ sequence. Above the mfs of the L₁ sequence only the Germanic forms remain.     

The Pragian-Emsian conodont successions of the Barrandian area: search of an alternative to the GSSP polygnathid-based correlation concept

Six Pragian-Emsian boundary sections in the Barrandian area, western of Prague, provided evidence of well detectable entries of Latericriodus fauna probably at the earliest Emsian beds (particularly Latericriodus bilatericrescens gracilis Bultynck). The chance to find icriodontid conodonts increases with latest part of Praha Fm., which is apparently of Emsian age, whereas polygnathids are sparsely preserved to absent. The high icriodontid/polygnathid ratio links together all these Barrandian sections, although their open-sea depositional environments range widely from deep troughs with rapid calciturbidite accumulation (Pod Barrandovem section) to relatively starving slope environments on elevations (Na Po?árech sections). The reports on polygnathid occurrences around the Pragian-Emsian boundary beds of the Barrandian area are much biased by poor reproducibility of the results (the conodonts cannot be found again) as well as by different levels where they were randomly found and/or by major taxonomic problems with the “kitabicus” and “dehiscens” definitions and their stratigraphic use. Apart from the GSSP in the Zinzilban Gorge (Uzbekistan) and its “kitabicus” boundary, the newly introduced “gracilis” biostratigraphic-marker concept preserves the major volume of the Pragian and respects also approximately the base of the traditional Emsian. These “gracilis” entries are clustered around the dark-colored “graptolite-bearing interval” beds, which largely form a prominent lithological marker within the latest, light gray-colored Dvorce-Prokop Limestone of the Barrandian area. This “gracilis” biostratigraphic marker has a promising correlation potential relative to Spanish and Moroccan sections.     

Evidence of photosymbiosis in Palaeozoic tabulate corals

Coral reefs form the most diverse of all marine ecosystems on the Earth. Corals are among their main components and owe their bioconstructing abilities to a symbiosis with algae (Symbiodinium). The coral–algae symbiosis had been traced back to the Triassic (ca 240 Ma). Modern reef-building corals (Scleractinia) appeared after the Permian–Triassic crisis; in the Palaeozoic, some of the main reef constructors were extinct tabulate corals. The calcium carbonate secreted by extant photosymbiotic corals bears characteristic isotope (C and O) signatures. The analysis of tabulate corals belonging to four orders (Favositida, Heliolitida, Syringoporida and Auloporida) from Silurian to Permian strata of Europe and Africa shows these characteristic carbon and oxygen stable isotope signatures. The δ¹⁸O to δ¹³C ratios in recent photosymbiotic scleractinians are very similar to those of Palaeozoic tabulates, thus providing strong evidence of such symbioses as early as the Middle Silurian (ca 430 Ma). Corals in Palaeozoic reefs used the same cellular mechanisms for carbonate secretion as recent reefs, and thus contributed to reef formation.     

Ichnostratigraphic correlation of Lower Palaeozoic clastics in the Kufra Basin (SE Libya)

The Lower Palaeozoic deposits in North Africa are dominated by sandstones and shales which often lack biostratigraphically useful body fossils. Trilobite burrows ( Cruziana ) partly fill this gap and provide the basis for medium-resolution stratigraphic interpretations. Several Ordovician-Silurian ichnostratigraphically significant Cruziana forms have been found and studied in the Kufra Basin (SE Libya), including C. goldfussi and C. furcifera from the Lower Ordovician Hawaz Fm. and a new ichnospecies, C. kufraensis , occurring in transgressive sandstones at the base of the Lower Silurian Tanezzuft Fm. The upper Tanezzuft Fm. and Akakus Fm. typically contain C. acacensis , a form that is characteristic of the Lower Silurian of Northern Gondwana.     

AnOistodus venustus-like conodont species from the Middle Ordovician of Baltoscandia

Ordovician conodont specimens resemblingOistodus venustus Stauffer, 1935 have been reported from many areas. There is increasing evidence, however, that several lineages with homeomorphic conodont elements have erroneously been referred to one and the same species. I have investigated Baltoscandian conodont elements of this kind in order to find out about their origins and phylogenetic relationships with morphologically comparable elements from other areas. A natural grouping of finds from the Middle and lower Upper Ordovician of Baltoscandia is here described as belonging to a new species of a new genus,Venoistodus balticus n. gen., n. sp. The new species probably evolved paedomorphically fromDrepanoistodus forceps (Lindström, 1955) in the Early Ordovician.     

An Evaluation of the Recently Proposed Palaeozoic Gastropod Subclass Euomphalomorpha

The recently proposed subclass Euomphalomorpha Bandel and Frýda, 1998 was primarily based on an openly coiled, planispiral initial whorl. Here, the protoconch of Carboniferous euomphalids is described and figured in detail previously unknown. This protoconch comprises distinctly less than one planispiral whorl with an abrupt transition to the telecoconch. It is umbilicate or openly coiled. Umbilicate or bilaterally symmetrical protoconchs are still present in Recent species of the Cocculiniformia, the Neomphalidae and the Docoglossa. A previously suggested close phylogenetic relationship between the euomphalids and primitive gastropod limpets is therefore corroborated by the protoconch morphology. The fact that several Palaeozoic gastropods, unlike most modern gastropods, have an openly coiled initial whorl is highly remarkable, but the meaning of this feature for the phylogeny and the systematics of the Gastropoda is not yet clear.