Conodont Evolution Research Articles

Increasing control over biomineralization in conodont evolution

Vertebrates use the phosphate mineral apatite in their skeletons, which allowed them to develop tissues such as enamel, characterized by an outstanding combination of hardness and elasticity. It has been hypothesized that the evolution of the earliest vertebrate skeletal tissues, found in the teeth of the extinct group of conodonts, was driven by adaptation to dental function. We test this hypothesis quantitatively and demonstrate that the crystallographic order increased throughout the early evolution of conodont teeth in parallel with morphological adaptation to food processing. With the c-axes of apatite crystals oriented perpendicular to the functional feeding surfaces, the strongest resistance to uniaxial compressional stress is conferred along the long axes of denticles. Our results support increasing control over biomineralization in the first skeletonized vertebrates and allow us to test models of functional morphology and material properties across conodont dental diversity.

Biodiversity and evolutionary phases of Lochkovian (Lower Devonian) conodonts in the Pyrenees: A comparative study

This paper aims to evaluate the zone-by-zone changes in Lochkovian conodont biodiversity in the Pyrenees region and compare the results with previous studies. Additionally, the paper seeks to identify evolutionary phases within the Lochkovian. We analyse the stratigraphic range data from eight classical Pyrenean Lochkovian sections. A total of 48 taxa at the species level, primarily confined to the Lochkovian, are included in the analysis. We employ both qualitative and quantitative approaches, including Clark's method for the conodont evolution index and Foote's parameters for measuring taxonomic diversity and rates. The zonal scheme employed in this study follows the global three-fold subdivision of the Lochkovian stage, with additional subdivisions based on local records. The zone-by-zone analysis of stratigraphically well-controlled successions contributes to our understanding of the conodont diversity dynamics in this region. The results are consistent with previous studies, but also highlight the unique aspects of the Pyrenean conodont record. Their highest diversity occurs in the middle Lochkovian within the kutscheri-pandora beta Zone, succeeded by an extinction event towards the end of this interval. Following a brief proliferation of species at the onset of the upper Lochkovian, another extinction event concludes this Stage. Results from all different rate measurements applied to Pyrenean Lochkovian conodonts are in disagreement with the prevailing perspective suggesting an escalation in the proportion of singletons and a concomitant decline in per-taxon rates with an increase in interval length. Comparative analysis of conodont records across various regions (Carnic Alps, Prague Synform, Central Nevada, and the Pyrenees) during the Lochkovian reveals significant differences in biodiversity, taxonomic composition, and zonal distribution.

Upper Triassic (middle Norian) conodont biostratigraphy succession from Qamdo, eastern Tibet

The Late Triassic is a critical period that witnessed major biological and environmental events. The geographic range and taxonomic diversity of conodonts were significantly changed during the Late Triassic, with the geographic range contracting prior to complete extinction of the group near the end of the Triassic. In the present study, we recognize for the first time a continuous middle Norian (Upper Triassic) conodont succession from the Qamdo (Changdu) area, eastern Tibet (Xizang), which was part of the North Qiangtang and Qamdo-Simao Block (NQ-QSB) located in the northeastern Tethys Ocean during the Late Triassic. Four conodont zones are established from the middle Norian (Alaunian) of the Chaiwei section in Qamdo, and in ascending order these are: the Epigondolella spiculata Zone, the Orchardella elongata Zone, the Mockina postera Zone, and the E. serrulata Zone; the neighboring Tuoba section also records these four zones, in addition to the upper lower Norian (upper Lacian) Ancyrogondolella uniformis Zone. All of these zones (except for the M. postera Zone) have been recognized for the first time in eastern Tibet. The Lacian-Alaunian boundary is tentatively placed at the level of sample CW-3 at the Chaiwei section and at the level of sample TBL-36 at the Tuoba section by the first occurrence (FO) of E. spiculata in each section. The position of the Alaunian-Sevatian boundary (ASB) is uncertain since the conodont assemblage from the top of the Bolila Formation at the study sections lacks age-diagnostic elements. The conodonts recovered from the Qamdo area have not only dated the Bolila Formation but also refined the conodont biostratigraphic zonation of the Alaunian in the study area. This allows improved correlation between the faunas of Qamdo and their counterparts elsewhere in Tibet and Europe, although the conodont zonations from these regions display lower precision than those established from North America. The Alaunian conodont faunas at Chaiwei and Tuoba appear to be dominated by juvenile specimens; this often appears to be the case in the Alaunian of the Tethyan Realm, but seems not occur in North America. This may suggest that the conodonts living in these two realms may have inhabited different ecological environments. The faunal turnover around the Lacian-Alaunian transition, with the evolution of Epigondolella, Orchardella, and Mockina from Ancyrogondolella, can be recognized in both study sections, although it is more remarkable in the Tuoba section. Although the lack of previous detailed studies of Norian conodont biostratigraphy from Tibet hampers correlation in this region and beyond, this study demonstrates the possibility of establishing high-resolution conodont biostratigraphic successions from Tibet in the future, since the conodont faunas recognized from Tibet and adjacent areas (e.g., Baoshan) suggest that relatively complete Norian strata exist in these regions. Overall, this study also provides new data to improve our understanding of conodont evolution during the Alaunian, and is significant in providing palaeontological data for studying the palaeogeographic evolution of eastern Tethyan ocean basins in the Late Triassic.

Temperature-driven heterochrony as a main evolutionary response to climate changes in conodonts.

Can we predict the evolutionary response of organisms to climate changes? The direction of greatest intraspecific phenotypic variance is thought to correspond to an 'evolutionary line of least resistance', i.e. a taxon's phenotype is expected to evolve along that general direction, if not constrained otherwise. In particular, heterochrony, whereby the timing or rate of developmental processes are modified, has often been invoked to describe evolutionary trajectories and it may be advantageous to organisms when rapid adaptation is critical. Yet, to date, little is known empirically as to which covariation patterns, whether static allometry, as measured in adult forms only, or ontogenetic allometry, the basis for heterochrony, may be prevalent in what circumstances. Here, we quantify the morphology of segminiplanate conodont elements during two distinct time intervals separated by more than 130 Myr: the Devonian-Carboniferous boundary and the Carnian-Norian boundary (Late Triassic). We evidence that the corresponding species share similar patterns of intraspecific static allometry. Yet, during both crises, conodont evolution was decoupled from this common evolutionary line of least resistance. Instead, it followed heterochrony-like trajectories that furthermore appear as driven by ocean temperature. This may have implications for our interpretation of conodonts' and past marine ecosystems' response to environmental perturbations.

General regularities in the development Gzhelian-Asselian conodonts

Subject of study. The features of the evolutionary changing of Gzhelian-Asselian conodonts are examined. Materials. The data on Ural and North American conodonts are used. Results. The cyclic type of change of the Pa-element morphology in the process of the evolutionary development of the representatives of the genus Streptognathodus is established. Morphological evolutionary trends of gradual development alternate with the periods of the rapid appearance of a group of the forms of original constitution. The species of this group are characterized by wide distribution and short lifetime. Such species are used as the markers of the boundaries of stratigraphic subdivisions. Lower boundary of Gzhelian is determined by the appearance of species of the group simulator; the species of group isolatus mark lower boundary of Asselian. Model of the ensemble evolution of the related species is used for explaining the directed change in the morphology of conodonts. The saltational appearance of the determined indication is explained by the phenomenon of evolutionary oscillations. Conclusion. We can make conclusion about the sexual multiplication of this group of the organisms according the established alternation of the periods of the slow and rapid morphological evolution of conodonts.

The last phase of conodont evolution during the Late Triassic: Integrating biostratigraphic and phylogenetic approaches

For the Upper Triassic, conodonts are the primary tools utilized in biostratigraphic investigations. For an effective biostratigraphic zonation, the species should be constrained by clear phylogenetic relationships, in which the stratigraphic ranges and taxonomy are reliable. Unfortunately, a phylogenetic framework for the Late Triassic pectiniform conodonts is almost missing, except for particular intervals, such as the Carnian/Norian boundary. The purpose of this study is to examine the latest Norian and Rhaetian pectiniform conodonts in detail in an attempt to determine their phylogenetic relationships, by applying novel phylogenetic methodologies that incorporate both morphological and stratigraphic data. This work is based on the conodont assemblages from the Upper Triassic strata of the Lagonegro Basin (southern Apennines, southern Italy) and the Csővár area (north-central Hungary), complemented with data from the literature. The calibrated phylogenetic analysis of the latest Norian and Rhaetian conodonts supports a two-step evolutionary history: a first radiation (~211–210 Ma) of the Parvigondolella species and the first representative of the genus Misikella, followed by a second phase (~206.5–205 Ma) leading to the final radiation of the Misikella species. Furthermore, the systematic revision of uppermost Triassic conodonts is provided along with the description of Misikella kolarae n. sp.

Conodont association of the Bashkirian-Moscovian boundary interval of the Donets Basin, Ukraine

Ten sections spanning the Bashkirian-Moscovian boundary interval were studied in the Donets Basin. Six of them contain most representative conodont and foraminifer associations. In this paper we focused on three the most complete sections that include stratigraphically important conodont species, which belong to the Declinognathodus, Idiognathoides, Idiognathodus, Neognathodus, “Streptognathodus”, Mesogondolella and Diplognathodus genera. The majority of those species are widely distributed, which makes the correlation to other areas reliable. Two biotic events in conodont evolution were discovered in these sections. Two conodont lineages established here are considered as potential markers for the definition of the lower boundary of the Global Moscovian Stage: D. marginodosus – D. donetzianus and Id. sulcatus sulcatus – Id. postsulcatus. The conodonts D. donetzianus and Id. postsulcatus, both proposed before as potential markers for the de? nition of the GSSP at the Bashkirian-Moscovian boundary, are described and compared to those from the other areas. The entry of D. donetzianus is updated and con? rmed to the top of the limestone K1 in both sections, the Zolota Valley and the Malo-Mykolaivka sections. The other proposals for the de???? nition of the lower Moscovian boundary by conodonts are discussed. Three conodont zones characterize the Bashkirian-Moscovian boundary interval. These are, in ascending order: the Id. tuberculatus – Id. fossatus Zone and D. marginodosus Zone from the upper Bashkirian, and D. donetzianus Zone from the lower Moscovian. They were recently described and shortly given in this paper.

Middle Triassic conodont assemblages from the Germanic Basin: implications for multi-element taxonomy and biogeography

Conodonts have been a key tool for biostratigraphical, evolutionary and palaeobiogeographical studies, and the Germanic Basin has been one of the most important regions for these studies. However, few modern studies provide systematic data on the mainly endemic conodonts of the Middle Triassic Germanic Basin. Here we document conodonts from two sections in Germany, one Bithynian in age and the other late Anisian to early Ladinian in age. The two sections captured two episodes of marine fauna invasion in the Germanic epicontinental basin during the Middle Triassic. The conodont Neogondolella mombergensis, elsewhere reported as appearing globally, is reviewed and revised, confirming previous suggestions that this species only occurs in the Germanic Basin. Apparatuses of Neogondolella haslachensis and Nicoraella germanica from the Germanic Basin are proposed. It was generally expected that S and M elements within clades have a very high morphological stability compared to P elements. However, the apparatus of Nicoraella germanica differs significantly from that of south China, indicating that the morphology of S elements within a genus can be unstable, and thus promotes our understanding of conodont evolution. The rarely documented genus Gondolatus, which was suggested as representing pathological specimens, is confirmed as a valid genus in the Germanic Basin. Our data suggest that endemic conodonts evolved twice, not only in the Upper Muschelkalk Subgroup, but also in the Lower Muschelkalk Subgroup.

Translating taxonomy into the evolution of conodont feeding ecology

Conodont research has long been divided between utilitarian applications to solve geological problems versus analysis of their paleobiology. However, recent advances in conodont functional analysis allow these independent stands of research to be unified, decoding the functional implications of their morphological variation. We demonstrate this using synchrotron tomography and finite element analysis, informed by occlusal and microwear analyses, to analyze functionally the classic evolutionary sequence of the genus Polygnathus. Our study shows that the evolution of the platform in Polygnathus occurred to accommodate and dissipate the stress accumulation derived from the tooth-like function that the P 1 elements performed, suggesting that this recurrent motif of conodont evolution represents an adaptive response to recurrent functional selective pressures. Our study establishes a framework in which the functional ecology of conodonts can be read from their rich taxonomy and phylogeny, representing an important attempt to understand the role of this abundant and diverse clade in the Phanerozoic marine ecosystems.

Dating of Cambrian-Ordovician boundary strata in northernmost Vietnam and methodological aspects of evolutionary biostratigraphic inference

Unrepeatability of evolution and the correspondence of the fossil record to ancestor-descendant successions of species are the unavoidable, although usually hidden, assumptions in any reliable age determination based on fossils. We expose these assumptions while dating early Paleozoic carbonate rock deposits in the Lung Cu section at the Vietnamese/Chinese border. The best-preserved and most abundant fossils in this section are shumardiid trilobites. The succession of shumardiid species, based on data from elsewhere, provides an evolutionary reference standard. The shumardiid record is not sufficiently complete to verify hypotheses of ancestor-descendant relationships but enables estimation of the "degree of evolutionary advancement" of the Vietnamese species. This suggests an age close to the Cambrian/Ordovician boundary. Although considered non-scientific by cladists, such inferences are testable. Support for a late Furongian or early Tremadocian age is provided by the occurrence of Cordylodus conodonts in strata above the trilobite-bearing bed. The conodont evolution has a good fossil record interpreted in population terms in the Baltic region and Australia, including the lineage represented in Vietnam. Age determination based on such evolutionary reasoning is reliable but of a relatively low resolution, because the rate of morphological evolution is generally low. Generally, more precise dating is offered by distribution of fossils controlled by ecological factors, which are repeatable and mostly diachronous over large geographic distances, but they may have happened relatively rapidly. The appearance of the Iapetognathus-Chosonodina-bearing conodont assemblage in the Lung Cu area, as suggested by its occurrences elsewhere, was probably due to abrupt faunal migration into the region.

Changhsingian conodont succession and the end-Permian mass extinction event at the Daijiagou section in Chongqing, Southwest China

Previous studies suggested rapid evolution of conodonts across the Permian–Triassic boundary (PTB), and the end-Permian mass extinction pattern varies in different sections in South China. Here we document a high-resolution conodont succession from a carbonate facies of the Changhsingian Stage and across the PTB at the Daijiagou section, about 35km north to Chongqing City, Southwest China. Two genera and twelve species are identified. Seven conodont zones are recognized from the uppermost part of the Lungtan Formation to the lowest Feixianguan Formation. They are the Clarkina liangshanensis, C. wangi, C. subcarinata, C. changxingensis, C. yini, C. meishanensis, and Hindeodus parvus zones in ascending order. Based on the high-resolution biostratigraphical framework at Daijiagou, the end-Permian mass extinction was rapid and it began in the base of the Clarkina meishanensis Zone. Associated with the extinction, a negative excursion of δ13Ccarb started in the middle part of Clarkina yini Zone with a progressive shift of 1.6‰ to the middle part of the Clarkina meishanensis, followed by a sharp shift of 3.51‰ from the Clarkina meishanensis Zone to the Hindeodus parvus Zone. Our study also suggests that the Triassic index species Hindeodus parvus co-occurred with Hindeodus changxingensis and Clarkina zhejiangensis and directly overlies the Clarkina meishanensis Zone at the Daijiagou section. All these data from the Daijiagou section and some previous studies of other sections in Sichuan, Guizhou provinces and Chongqing City suggest that the first occurrences of Hindeodus parvus are slightly earlier than the sharp negative excursion of δ13Ccarb and the FAD at the Meishan GSSP section. We consider that the slight difference of the end-Permian mass extinction, chemostratigraphy and conodont biostratigraphy at Daijiagou and its adjacent areas is most likely subject to different lithofacies, fossil preservation, and the constraint on the stratigraphic resolution rather than a different tempo of the end-Permian mass extinction in a global sense. The whole Changhsingian conodont succession at Daijiagou provides a high-resolution correlation with other equivalent sections in the Palaeotethys. The controversial results of biostratigraphy and chemostratigraphy between the sections investigated in this paper and the Meishan GSSP section also provide some important implications that accurate chronocorrelation requires the evaluation of multiple, varied stratigraphcal signals rather than relying solely on the FAD of the Triassic index species Hindeodus parvus for recognizing the Permian–Triassic boundary (PTB). Growth series of abundant specimens for each species are figured. The taxonomy of some Hindeodus species in the PTB interval is updated.

Evolutionary roots of the conodonts with increased number of elements in the apparatus

ABSTRACTFour kinds of robust elements have been recognised inAmorphognathus quinquiradiatusMoskalenko, 1977 (inKanyginet al. 1977) from the early Late Ordovician of Siberia, indicating that at least 17 elements were present in the apparatus, one of them similar to the P1element of the Early SilurianDistomodus. The new generic nameMoskalenkodusis proposed for these conodonts with a pterospathodontid-like S series element morphology. This implies that the relatedDistomodus,PterospathodusandGamachignathuslineages had a long cryptic evolutionary history, probably ranging back to the early Ordovician, when they split from the lineage ofIcriodella, having a duplicated M location in common. The balognathidPromissum, with a 19-element apparatus, may have shared ancestry withIcriodellain Ordovician high latitudes, withSagittodontina,Lenodus,TrapezognathusandPhragmodusas possible connecting links. The pattern of the unbalanced contribution ofBaltonioduselement types to samples suggests that duplication of M and P2series elements may have been an early event in the evolution of balognathids. The proposed scenario implies a profound transformation of the mouth region in the evolution of conodonts. The probable original state was a chaetognath-like arrangement of coniform elements; all paired and of relatively uniform morphology. This was modified at the origin of protopanderodontids by the introduction of a medial S0element, which resulted in the separation of the exposed unit of M and S series elements from the P series elements hidden in the throat. A rotation of the S series elements to an almost horizontal position in early prioniodontids may have promoted duplication of the M element pair. InGamachignathus,IcriodellaandPterospathoduslineages, these elements are differentiated morphologically. Subsequent anteriorward bending of the P element series caused duplication of the balognathid P2element pair, but they remained undifferentiated, even in the otherwise elaboratePromissum. The whole clade of conodonts with supernumerary element pairs in the apparatus has its roots in high latitudes of the Ordovician.

Parafurnishius, an Induan (Lower Triassic) conodont new genus from northeastern Sichuan Province, southwest China and its evolutionary implications

A fundamental aspect of taxonomy at the generic level, critical to understand Early Triassic conodont evolution, is the composition of the multielement apparatus. In this paper, we document a platform-bearing new conodont genus, Parafurnishius n. gen., as well as its multielement apparatus from the Griesbachian Feixianguan Formation (Lower Triassic) in Xuanhan County, northeastern Sichuan Province, southwest China. The new conodont genus is characterized by numerous robust and irregularly distributed conical denticles with variable platform morphology that has a possible affinity with the P1 elements of Furnishius. These genera have apparatuses similar to those of Ellisonia and are classified with the family Ellisoniidae. The strong intraspecific variation of P1 elements and the growth series within the entire sample population suggest that Parafurnishius may have evolved from the Griesbachian Isarcicella by developing random denticle positioning away from the platform centre, and then possibly evolved into younger Triassic Furnishius by developing a stable blade configuration. This preferred interpretation implies an ellisonid apparatus for Isarcicella. Alternatively, Parafurnishius may have evolved from Ellisonia and developed a homeomorphic P1 element with Isarcicella. This new taxon has strong intraspecific variation of denticle growth orientation during the Early Triassic.

Revised conodont zonation and conodont evolution across the Permian–Triassic boundary at the Shangsi section, Guangyuan, Sichuan, South China

Large conodont samples (20 kg at most) have been collected from the uppermost Permian and the lowermost Triassic (beds 26–33) at Shangsi, northern Sichuan. These have enabled us to establish parallel hindeodid and gondolellid conodont zones through the section similar to previously recognized in the Meishan section. In ascending order, three newly established gondolellid zones at the Shangsi section are: Neogondolella yini Zone (bed 26), Neogondolella meishanensis Zone (beds 27a–27c), Neogondolella taylorae Zone (beds 28a–29 d). Also in ascending order, four revised or newly established hindeodid zones are: Hindeodus changxingensis Zone (beds 28a–29b) Hindeodus parvus Zone (beds 29c–30a), Isarcicella lobata Zone (beds 30b–31a), Isarcicella isarcica Zone (bed 31b and above). According to the new data, the first occurrence of H. parvus is about 2 m lower than the previously reported horizon. On the basis of both hindeodid and gondolellid taxa, the PTB is placed 22 cm above the base of bed 28a. This conodont zonation of the Shangsi section will help improve correlations of global Permian–Triassic boundary sections.

Generic turnovers of Carnian/Norian conodonts: Climatic control or competition?

Pizzo Mondello section (western Sicily, Italy) yields a very rich conodont record, ranging from Late Carnian to Rhaetian in age, shedding new light into the evolution of conodonts across the Carnian/Norian boundary. Conodont biostratigraphy around the Carnian/Norian boundary is still problematic due to an inferred provincialism that affects most of the conodont species and to the occurrence of a great number of transitional forms, linked to the fast recovery of conodonts after the Middle Carnian crisis. The lower 144 m of the succession, Tuvalian to Lacian in age, were sampled in detail for a biostratigraphic and ecological study of five Upper Triassic conodont genera: Paragondolella, Carnepigondolella, Metapolygnathus, Epigondolella, and Norigondolella. After a taxonomic revision of the genera studied, meant to define the most significant morphological features for their classification, a statistical approach was applied to the study of conodont populations. Quantitative curves of the absolute abundances for each genus show potential ecological competition between Paragondolella– Carnepigondolella and later between Metapolygnathus– Epigondolella (and partially between Epigondolella– Norigondolella). Recognition of morphoclines among species, integrated by a similar ecological behaviour, supports the phylogenetic derivation of Norigondolella and Metapolygnathus from Paragondolella and that of Epigondolella from Carnepigondolella. Furthermore, cross checks of the quantitative curves evidenced the presence of three major assemblage changes: at metre 64.76 (named event T1) Carnepigondolella is replaced by its descendant Epigondolella in an evolutionary step; at metre 80 (event T2) Epigondolella is substituted by the mass occurrence of Metapolygnathus and at metre 95 (event T3) Metapolygnathus is succeeded by advanced Epigondolellae species and by Norigondolella. In looking for environmental explanations to these biological events, the conodont assemblages are compared to coeval δ 18O and δ 13C isotopic curves, based on new data from Pizzo Mondello. From the comparison, a correspondence appears between higher 13C/ 12C ratios and the interval between events T2–T3, but not with event T1. This is in accordance with the interpretation of event T1 as an evolutionary turnover. In more detail, we observe the possible influence of environmental conditions on the absolute abundances of all the studied genera: while Epigondolella proliferate when seawater δ 13C ranges between 2.1‰ and 2.5‰ , Carnepigondolella proliferate in the range between 1.6‰ and 2.1‰; Metapolygnathus instead appears to be limited to environmental conditions related to higher δ 13C values in the seawater. We explain this behaviour by interpreting the genus Metapolygnathus as an opportunist taxon, exactly as its forerunner, the genus Paragondolella.

Conodont diversity and evolution through the latest Permian and Early Triassic upheavals

A study of latest Permian and Early Triassic multielement conodonts identifies eight steps in their evolutionary history during an interval when Earth's biosphere was highly stressed. These steps are: 1) gradual decline of families and genera through the Changhsingian (up to the late Griesbachian); 2) conodont biofacies change and extinction of Tethyan endemic species close to the Permian–Triassic Boundary (PTB); 3) faunal turnover with extinction and origination in the late Griesbachian; 4) initial radiation in gondolellids and diversification in apparatuses during the Dienerian; 5) explosive radiation in the early–middle Smithian; 6) major extinction in the late Smithian; 7) major radiation early in the Spathian; 8) gradual turnover and decline in the late Spathian through early Anisian. Conodontophorids were reduced from five families at the beginning of the Changhsingian to three by the PTB, and to two late in the Griesbachian. From the Changhsingian to the late Griesbachian, there was a single multielement apparatus represented in the Gondolellidae, whereas by the Olenekian there were at least twelve. Given absolute age constraints, the conodont recovery in the aftermath of the PTB was extraordinary. Conodont evolution during the Dienerian remains obscure but was very significant in terms of changes in multielement apparatuses. In spite of Induan extinctions, generic diversity generally increased from the PTB up to the late Smithian. In terms of species, genera, and multielement apparatuses, the acme of Triassic conodonts was in the middle Smithian, and the biggest extinction was in the late Smithian. After this extinction, generic and apparatus diversity quickly returned to high levels, marking a significant Spathian recovery. Gradual decline characterized the late Spathian and persisted into the early Anisian. A synthetic summary of the temporal distribution and proposed relationships amongst all known Lower Triassic conodonts provide an improved foundation for biostratigraphic and biochronologic studies. Extinction and radiation trends correlate well with sea-level changes and sequence boundaries: faunal turnovers correspond to lowstands in the late Griesbachian, late Smithian, and late Spathian, and radiations correspond to transgressions in the early Griesbachian, early Smithian, and early Spathian. The trends also correlate with perturbations in the carbon cycle, with Lower Triassic δ 13C minima corresponding to extinction and faunal turnover, and positive values generally occurring during radiations. However, Middle Triassic recovery of marine benthos follows a positive maxima and an overall decline in conodont diversity. New taxa Borinella chowadensis, B. megacuspa, Neogondolella griesbachensis, and N. mongeri are described.

Environmental and biotic changes across the Permian–Triassic boundary in western Tethys: The Bulla parastratotype, Italy

The sedimentary and biotic evolution of a 190 m interval of shallow marine and lagoonal facies in the Bellerophon and Werfen formations in the Southern Alps has allowed comparison of western with eastern Tethys: Meishan D section (southern China), Salt Range (Pakistan) and Abadeh (Iran). Results are as follows: (1) The upper part of the Bellerophon Fm. (Changhsingian changxingensis–deflecta Zone) shows only modest biotic variation connected with tectonically driven local variation and perhaps to more general climatic variation. The δ 13C decrease starting in the uppermost 30 m of the Bellerophon Fm. is correlated with decrease in global organic productivity starting about 1 m below the PTB in Chinese sequences and 20 m below in the Abadeh section. This interval culminated in a regression truncated by an unconformity–paraconformity (Unconformity 1). (2) The uppermost Bellerophon Fm. is a ca. 1 m transgressive-regressive sedimentary cycle, the informally named Bulla Mbr (Changhsingian: Early praeparvus Zone). The maximum flooding interval of this unit possibly had a slight increase in biodiversity, mainly in foraminifers, algae and brachiopods. The high increase in biodiversity previously reported may, in part, reflect abundance of biota and organic matter reworked into transgressive and regressive intervals. We suggest partial correlation of the basal unconformity of the Bulla Mbr (Unconformity 1) with the regressive uppermost Bed 24e of the Meishan D section marking the disappearance of foraminifers and algae in the eastern Tethys. We also suggest diachronous disappearance of benthic taxa in Tethys, with the Southern Alps acting like a refugium. (3) The main extinction (first extinction phase, mainly regarding foraminifers) in the Southern Alps occurred in a thin ca. 25 cm interval including the uppermost regressive Bulla Mbr, Unconformity 2, and possibly, the basal transgressive bed of the Tesero Mbr of the Werfen Fm. This interval is correlated in part with regressive Bed 26 of Meishan D section. The main decrease in abundance and biodiversity in the Southern Alps coincides with appearance of small oolites with crystalline outer cortex near the basal transgressive tract of the lower Tesero Mbr, a ca. 220 cm sedimentary cycle, that is followed by extension of microbialitic layers alternating with veritable biostromes with brachiopods and byssate bivalves as salient components among the algae. Vacated niches favored evolution of conodonts. Hindeodid conodont biodiversity increased with species developing characteristics of Isarcicella. This interval has been referred to the Changhsingian Late praeparvus Zone and correlated with Bed 27a–b of Meishan D section. The PTB has been identified in the Bulla section at 1.30 m from the base of the Werfen Fm. – with the first appearance of Hindeodus parvus defining the base of the parvus Zone – in a microbialitic layer correlated with Bed 27c of Meishan D section. Around the PTB the major part of the remaining Permian biota disappeared. Gymnocodiacean algae were the last group to undergo extinction within the Triassic layers. (4) Biodiversity dropped severely in the succeeding bioturbated microbialitic interval from which conodonts are absent. More humid climate is reflected in a more sandy marine substrate inhabited by Lingula, Unionites and Claraia. Conodonts recurred in the schizohaline upper part. The succeeding entry of the biozonal markers Isarcicella lobata, Isarcicella staeschei and Isarcicella isarcica allow discrimination of three conodont biozones. The layer with entry of I. staeschei has been aligned with Bed 28 of Meishan D section. The main extinction phase in the western Tethys seems to correspond to a gradual but swift transition from acid-bath to alkaline-bath according to the Deev Jahi model of Heydari and Hassanzadeh [Heydari, E. and Hassanzadeh, J., 2003. Deev Jahi model of the Permian–Triassic boundary mass extinction: a case for gas hydrates as the main cause of biological crisis on Earth. Sed. Geol., 163, 147–163.]. The Bulla section with abundant data on biotic and depositional variation is here considered as the PTB parastratotype for the shallow marine western Tethys.

Conodont evolution and stratotype sign of carboniferous Tournaisian-Visean boundary in South China

A stratotype section, boundary point and conodont sign have been recommended for GSSP of the Tournaisian-Visean boundary, based on studies of sectional sedimentology, conodont facies and phylogeneses in South China. Two areas representing margin and inner of the Yangtzi Plate and three sections of different facies were chosen, i.e. the Longdianshan section of the platform facies in Liuzhou of Guangxi, the Yudong section of the ramp facies in Shidian of Yunnan and the Pengchong section of the basin facies in Liuzhou of Guangxi. Stratigraphic frameworks of two areas were set up by systematical studies of carbonate facies and cycles. Conodont facies-distribution and paleoecologic conditions were researched on statistics of fossil variation and richness, and a kind of planktonic conodont, gnathodids that were widespread, is chosen to select the sign-fossil from it. Seven conodont pedigrees were supplemented or erected by studies of statistics and transitional forms. Conodont evolution in the Early Carboniferous could be divided into three stages, i.e. the Siphonodella stage, the Gnathodus typicus stage and the Gnathodus bilineatus stage. The transform-surface between the later two stages could be put as the Tournaisian-Visean boundary. Finally, this paper proposes that the Pengchong section can be the stratotype candidate of the Tournaisian-Visean boundary, the boundary point be put at the bottom of bed 58 and the stratotype sign of conodont be the first occurrence of Gnathoalus praebilineatus of the Gnathodus semiglaber branch.

Strategies of survival during extreme environmental perturbations: evolution of conodonts in response to the Kellwasser crisis (Upper Devonian)

The size and shape evolution of two conodont genera surviving the Kellwasser period, Icriodus and Palmatolepis, has been quantified using a Fourier analysis of the outline of platform elements. Morphological variations of both genera in response to environmental fluctuations are comparable, although slightly shifted in time, suggesting a differential sensitivity to the environmental variations due to differences in favored habitats. The period of the crisis comprises two anoxic events of increasing importance and impact on the biosphere. For each event, the post-crisis conodont elements are smaller than those found before and exhibit extreme morphs, while the recovery period is characterized by an increase in size and inverse changes in shape; morphological trends are expressed with a lower amplitude during the first anoxic event. Strategies of morphological response are different for the two genera, implying heterochronic shifts or changes in the developmental pathway.

The importance of Hindeodus parvus (Conodonta) for the definition of the Permian-Triassic boundary and evaluation of the proposed sections for a global stratotype section and point (GSSP) for the base of the Triassic

The biostratigraphic Permian/Triassic (P/T) boundary is defined by the first appearance of H. parvus. The first appearance of H. parvus within the cline H. latidentatus-H. parvus is a globally recognizable event in the conodont evolution. The first appearance of H. parvus is not facies related and can be observed both in ammonoid-free shallow-water deposits and in ammonoid-bearing pelagic deposits. H. parvus is a common, easily determinable species known so far from the entire Tethys, Japan, western North America, Boreal realm (Greenland) and the Tethyan margin of Gondwana. H. parvus is the first species with world-wide distribution to appear after the absolute minimum in the faunal diversity indicated by the minimum in δ13C. The Meishan section (South China) contains a continuous, pelagic sedimentary record across the P/T boundary without stratigraphic gaps. It is nearly unaltered thermally (CAI = 1-1.5). Its fossil content (ammonoids, conodonts, foraminifers, bivalves, brachiopods, sporomorphs etc.) and event succession have been thoroughly studied. Absolute age and magnetostratigraphy have also been subjected to intensive studies. The section is readily accessible and under protection of the government. This section is best suitable as a global stratotype section and point (GSSP) for the base of the Triassic. No other section in the world is known to be qualified for defining the P/T boundary in a GSSP. H. parvus made its earliest appearence in the middle part of Boundary Bed 2 (Bed 27) at Meishan. It evolved within Bed 27 from H. latidentatus within a phylomorphogenetic continuum in a continuous and monofacial stratum. The biostratigraphic P/T boundary lies very close to the event boundary (15cm above the event boundary at the base of Boundary Bed 1 = Bed 25, and a few centimetres above the minimum in δ13C in the lower Boundary Bed 2).