Assesses the macroevolutionary turnover of paleotropical planktic graptolites during the Late Ordovician Mass Extinction (LOME) via automated sequencing and capture-mark-recapture modeling. Graptolites exhibited a succession of turnover pulses (sensu Elizabeth Vrba) that were coincident with the main phases of the Hirnantian glaciation and during which the Diplograptina experienced declining metapopulation size, elevated extinction, zero species originations, and ultimately, complete extermination. Concurrently, the Neograptina (latest Katian temperate zone immigrants) exhibit pulses of both extinction and adaptive radiation. Thus, the LOME involved intense species selection and the wholesale alteration of the clade diversity structure of a major element of the zooplankton. The LOME is unlikely to have been a direct effect of ocean anoxia or sampling bias but rather resulted from Hirnantian climate change, which altered nutrient supplies and plankton community compositions along with ecological displacement and loss of habitat that together drove the succession of turnover pulses. This title is also available as open access on Cambridge Core.

Received 25 March 2023 Accepted 30 March 2023 Available online 16 June 2023

Newly identified relay ramps and rhombochasms in the northern Appalachian Basin (NAB) require significant revision to the structural style, structural timing, and hydrocarbon migration components of the basin evolution model for the NAB. Relay ramps demonstrate that Neoacadian (Devonian) extensional tectonics affected the Devonian Marcellus Formation, earlier than the accepted Alleghanian (Carboniferous-Permian) tectonics. Relay ramps also confirm Ordovician Taconic extension affected the Ordovician Utica Group. Rhombochasms and possible Riedel shears in the Utica Group suggest a component of orogenparallel, strike-slip motion during the Taconic Orogeny. In western Pennsylvania, a three-dimensional (3-D) seismic survey reveals that relay ramps terminate straight segments of faults and kink bands along the southeast borders of asymmetric, Salina Group "salt" pillows. The relay ramps are consistent with a local extensional environment associated with evaporite and mud or mudstone withdrawal and transport. Devonian sediments infill the grabens linked with the salt pillows, indicating that the grabens and associated faults initiated during the Devonian Neoacadian orogeny. Since the faults predate hydrocarbon generation, they were potentially migration pathways for hydrocarbons. In New York State, Ordovician (Taconic) rhombochasms in the NAB are inferred from (1) grabens observed in 3-D seismic surveys that occur at right stepovers of northeast-striking faults south of the New York promontory on the Taconic Laurentian

Upper Ordovician planktic and benthic graptolites are generally rare in North Africa. Four localities in southern Morocco have yielded graptolitic material from the top of the First Bani Group and the Lower Ktaoua, Upper Tiouririne and Upper Ktaoua formations, the lithostratigraphic units that contain the Tafilalt Biota. Three species of planktic graptolite (in the genera Climacograptus, Diplograptus? and Neodiplograptus), six species of benthic graptolite (in the genera Dendrograptus, Callograptus, Ptilograptus and '`Dictyonema') and one probable hydroid (Webbyites? sp.) are described from these sites. Two species are new: `Dictyonema' khadijae sp. nov. and 'Dictyonema' villasi sp. nov. Another probable hydroid, a Plumalina-like form from the Lower Ordovician Fezouata Formation, is also illustrated. Some of the Tafilalt graptolites are similar to Bohemian species, indicating faunal links between the regions during the Late Ordovician. The graptolite dating of some isolated localities helps to evaluate the chronostratigraphic and lithostratigraphic assignment of those outcrops, implying an earlier appearance of the 'Dendrocystites fauna' (echinoderm-dominated: c. Sandbian 2-Katian 1) and a late placement for the 'Declivolithus fauna' (trilobite-dominated: c. Katian 2).

The Upper Ordovician Sandbian to Katian strata from the East Qilianshan (northeastern Tibet Plateau) bear a graptolite fauna of moderately high diversity. Graptolites from the Amplexograptus maxwelli beds to the Appendispinograptus longispinus Biozone (Sa2-Ka4 intervals) proposed herein include 27 species of 13 genera. This important graptolite fauna is first described herein although it was initially reported in 1963. Most of them occur in the A. longispinus Biozone corresponding to the Dicellograptus complexus to Paraorthograptus pacificus biozones of the Wufeng Formation in the Yangtze region. Alulagraptus newgenus is established based on the materials from the East Qiqiaogou section. The endemic species, e.g., Alulagraptus ensiformis (Mu and Zhang in Mu et al., 1963), Dicellograptus sinicus Mu and Zhang in Mu et al., 1963, and Climacograptus? papilio Mu and Zhang in Mu et al., 1963, could indicate that East Qilianshan block was separated from South China.

Although extinction risk has been found to have a consistent negative relationship with geographic range across wide temporal and taxonomic scales, the effect has been difficult to disentangle from factors such as sampling, ecological niche, or clade. In addition, studies of extinction risk have focused on benthic invertebrates with less work on planktic taxa. We employed a global set of 1114 planktic graptolite species from the Ordovician to lower Devonian to analyze the predictive power of species' traits and abiotic factors on extinction risk, combining general linear models (GLMs), partial least-squares regression (PLSR), and permutation tests. Factors included measures of geographic range, sampling, and graptolite-specific factors such as clade, biofacies affiliation, shallow water tolerance, and age cohorts split at the base of the Katian and Rhuddanian stages.The percent variance in durations explained varied substantially between taxon subsets from 12% to 45%. Overall commonness, the correlated effects of geographic range and sampling, was the strongest, most consistent factor (12-30% variance explained), with clade and age cohort adding up to 18% and other factors <10%. Surprisingly, geographic range alone contributed little explanatory power (<5%). It is likely that this is a consequence of a nonlinear relationship between geographic range and extinction risk, wherein the largest reductions in extinction risk are gained from moderate expansion of small geographic ranges. Thus, even large differences in range size between graptolite species did not lead to a proportionate difference in extinction risk because of the large average ranges of these species. Finally, we emphasize that the common practice of determining the geographic range of taxa from the union of all occurrences over their duration poses a substantial risk of overestimating the geographic scope of the realized ecological niche and, thus, of further conflating sampling effects on observed duration with the biological effects of range size on extinction risk.

Horizon annealing (HA) provides a method to order all horizons in a chronostratigraphic data set, including marker beds and isotopic excursions, as well as horizons that lack exact local markers (such as taxon first appearances) and are, thus, constrained only by local stratigraphical order. Global stratotype section and point (GSSP) levels placed within an HA composite succession can be precisely correlated with levels in all other sections in the composite that span the same interval. We present two approaches to the quantitative assessment of the uncertainty or error in the placement of horizons within the composite section: a permutation method (jackknife analysis) and a sensitivity analysis (the relaxed fit curve). From jackknife analysis, we calculate a standard deviation (sigma) of the variation in horizon placements and estimate the 95% confidence interval of the variation in horizon placement within the composite. We also directly assess the relative stability of event positions using the results of the jackknife. These approaches provide an objective method for assessing the relative strengths of GSSP candidates, in which we prefer those sections and horizons that are the most precisely controlled in the HA composite. Integration of biostratigraphical, chemostratigraphical and lithostratigraphical marker horizons into the HA process markedly improves levels of constraint within the composite compared to biostratigraphical data alone. In a temporally scaled composite, the 95% confidence intervals on horizon placements could be used to estimate temporal resolution. In our study, we estimate that the average temporal resolution is approximately 319 kyr, which approaches the range of that needed to test hypotheses of orbitally driven cyclicity.

The olenid trilobite Triarthrus commonly occurs in nearly monospecific assemblages within otherwise relatively barren black shales. As such, it has been proposed that these trilobites preferred dysoxic or even anoxic habitats and suggested feeding habits range from predation and particle feeding to chemoautotrophism. A unique bedding-plane assemblage of aligned traces that grade from Rusophycus to Cruziana, with associated Triarthrus beckii carcasses, are described from three localities in the Indian Castle Formation (upper Utica Shale) just below a K-bentonite bed. Although few body fossils are preserved, it is clear that the 15-cm-thick, laterally extensive Thruway K-bentonite created a unique taphonomic window that preserved the activities of numerous olenid trilobites. Rusophycus and Cruziana, consistently observed in densities above 100 trackways/m2, were excavated by the trilobites into the upper surface of a micro-graded bed, likely a distal turbidite deposit. Sedimentological and trace metal data (Mo, Mn, V and U) support dysoxic but not persistently anoxic conditions through this interval. Measurements from over 500 individual trackways have mean orientations of 259.1° (WSW) at the Myers Rd. locality and 224.59° (SW) at the Dolgeville Dam locality. These orientations are closely similar to independent sedimentological indicators of current transport direction at these sites, which indicates that the trilobites preferentially faced into the prevailing current. The trackways provide compelling evidence that Triarthrus beckii individuals were engaged in feeding, probably assisted by current transport of particles. These results do not support previous suggestions that Triarthrus may have relied upon a chemoautotrophic life habit, but are consistent with suggestions of predation or scavenging from the sediment.