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. Conodonts, early vertebrates, are thought to have evolved complex tooth tissue as an adaptation for feeding. Here, the authors use Electron Backscatter Diffraction to show increasing dental crystallographic order through conodont evolution, in parallel with dietary adaptations.

Two Lotagnostus-dominated faunas from the Windfall Formation at Ninemile Canyon in the Antelope Range of Nevada, USA, are described: an older Lotagnostus nolani Fauna and younger L. rushtoni Fauna. The former is dominated by two morphs of Lotagnostus, one strongly scrobiculate and the other smooth to weakly scrobiculate. Both morphs fall within the broad concept advocated for L. americanus by Peng et al. (2015). The numerous (>1400 sclerites) specimens of Lotaganostus in collections of the L. nolani Fauna confirm that the two morphs do not intergrade and remain distinct throughout ontogeny. Both display multiple traits that distinguish them from the type material of L. americanus, justifying treatment as separate species. Similarly unique, diagnostic features were identified to restore the Asian species L. punctatus and L. asiaticus to full species status, whereas deficiencies in the type material for L. americanus warrant restriction of the name to the holotype. New species described from the Windfall include five agnostoids (Lotagnostus nolani, L. clarki, L. morrisoni, L. rushtoni, and Neoagnostus parki) and one trilobite (Bienvillia eurekensis). Plicatolina nyensis Taylor is reassigned to Mendoparabolina on the form of its pygidium. Conodonts from the Catlin Member of the Windfall Formation and overlying informal Caryocaris shale member of the Goodwin Formation at Ninemile Canyon provide a late Sunwaptan (Eoconodontus Zone) age for the Lotagnostus rushtoni Fauna and assign the entire Caryocaris shale to the early Ordovician Rossodus manitouensis Zone. Combined with published data on trilobite faunas, the conodont faunas confirm strong diachroneity for the top of the Catlin, and a lack of overlap in age between the Caryocaris shale and Bullwhacker Member of the Windfall in ranges to the north and east. Co-occurrence of Lotagnostus nolani and Mendoparabolina nyensis establishes age equivalence of the L. nolani Fauna with the Hedinaspis-Charchaqia (HC) Fauna at the base of the Hales Limestone in the Hot Creek Range, and earlier correlations of the latter with the L. punctatus Zone in Asia are supported. However, isolation of the HC Fauna in starved-basin deposits above a major sequence boundary at the base of the Hales, and ecologic restriction of Lotagnostus to lower slope and basinal environments that prevented association with endemic shallow marine taxa, renders correlation into the biostratigraphy of Laurentian upper slope and platform imprecise on the order of 10s, if not 100s of meters.

A plethora of names has been applied to upper Cambrian and Lower Ordovician lithostratigraphic units distributed from western Utah to southeastern and central Nevada. We report comprehensive stratigraphic analysis utilizing lithologic, conodont, brachiopod, sequence stratigraphic, and carbon isotope data from several ranges in southeastern Nevada. Those data demonstrate that upper Cambrian to Lower Ordovician strata in that area belong to a variety of depositional systems that can be integrated into a comprehensive and functional depositional model that span carbonate tidal flat to shallow marine carbonate ramp to shelf to deep marine settings. Most of these strata should be placed within a single lithostratigraphic nomenclature based on the well-known Notch Peak Formation and House Limestone of western Utah. Strata of the Whipple Cave Formation in the South Egan Range, Nevada are reassigned to the three members of the Notch Peak Formation. Strata assigned to the Nopah Formation and Pogonip Group by geologic mappers who worked in the Delamar Mountains, Meadow Valley Mountains, Sheep Range, and Arrow Canyon Range in Nevada are reassigned to the Notch Peak Formation and overlying House Limestone. Coeval strata farther west record a deeper marine depositional setting and are appropriately assigned to the Windfall Formation and Goodwin Limestone. Conodonts and sequence stratigraphic packages identified from slope deposits of the Hales Limestone at Tybo Canyon in the Hot Creek Range allow correlation to the Notch Peak Formation and House Limestone in western Utah.

The Durness Group of NW Scotland records deposition on the Laurentian margin from the basal Miaolingian (Cambrian, 509 Ma) to the Dapingian-Darriwilian boundary interval (Middle Ordovician, 470.3-468.9 Ma). The 930 m thick succession of peritidal and subtidal carbonates was deposited on the Scottish promontory, a nearly 120 degrees deflection in the Palaeozoic continental margin between the Appalachian and Greenland sectors. These sediments were deposited as part of the Great American Carbonate Bank, a non-uniformitarian, continent-scale carbonate platform developed on the peneplaned craton. Measurement and description of a bed-by-bed composite section through the Durness Group provide a high-resolution reference framework that integrates conodont biostratigraphy, chemostratigraphy and sequence stratigraphy, including correlation with the Sauk megasequence and its subdivisions. The Sauk II-Sauk III sequence boundary marks the base of the group. The top of the group is faulted against rocks of the Moine thrust zone, generated by the Scandian orogeny, but sedimentation was probably terminated by the earlier Grampian arc-continent collision at 470-469 Ma. The highly mature quartz arenites of the underlying Ardvreck Group (Cambrian Series 2) indicate that there was no source-to-sink depositional continuity from the Hebridean foreland to the Dalradian Supergroup, which has coeval clastic sedimentary rocks of contrasting composition.

Influences of depositional setting and tectonics on recording Milankovitch (orbital) signals within evolving Ordovician foreland successions during arc-continent collision are poorly documented. To address this, we analyzed downhole gamma ray vs depth time series from three wells on the Central Appalachian foreland, eastern USA for evidence of Milankovitch forcing during the 25 Myr duration Middle and Upper Ordovician Darriwilian to Katian interval. Relatively slowly accumulating Darriwillian sabkha anhydritic dolomites (up to 450 m thick), are dominated by eccentricity and obliquity forcing whereas Darriwillian to Sandbian restricted inner ramp carbonates (350 m thick) show eccentricity forcing only as do the overlying basal Katian (80 m thick) mid-ramp units. Rapidly accumulating lower Katian deeper ramp, shale-prone sediments (400 to 500 m thick) and upper Katian peritidal siliciclastic units (similar to 300-550 m thick) show a full suite of short eccentricity, obliquity and precession forcing. Best recording of the astronomical signal occurred during Katian rapid tectonic subsi-dence whereas a much poorer record was preserved during the Darriwilian-Sandbian. Milankovitch forcing of climate influenced input of siliciclastics as well as controlling sea-level fluctuations and position of storm wave-base. Initially sea level changes may have been driven by greenhouse aquifer eustasy but following later Dar-riwilian cooling, glacio-eustasy was dominant.

Abstract Ordovician rocks, found in northern, east-central, interior and southern Alaska, formed in a variety of depositional and palaeogeographic settings. Shallow- and deep-water strata deposited along the northwestern Laurentian margin occur in east-central Alaska (Yukon River area) and probably correlative rocks crop out to the north in the Porcupine River area. Ordovician strata elsewhere in Alaska are parts of continental or island arc fragments that, as indicated by faunal and detrital zircon data, have been variously displaced. In northern Alaska, Ordovician rocks are included in the Arctic Alaska–Chukotka Microplate (AACM), a composite tectonic entity with a complex history. Some Ordovician strata in the AACM (parts of the North Slope subterrane) represent displaced fragments of the northern Laurentian margin. Coeval strata in southwestern parts of the AACM (York and Seward terranes, Hammond subterrane) share distinctive lithologic and biotic features with Ordovician rocks in interior Alaska (Farewell and related terranes). Ordovician strata in southeastern Alaska (Alexander terrane) also likely compose a composite crustal fragment that accumulated in a complex arc system. Shared features between many of these units suggest similar origins as part of one or more crustal fragments situated in the palaeo-Arctic between Laurentia, Baltica and Siberia during early Paleozoic time.

Conodonts were the first vertebrates to develop mineralized dental tools, known as elements. Recent research suggests that conodonts were macrophagous predators and/or scavengers but we do not know how this feeding habit emerged in the earliest coniform conodonts, since most studies focus on the derived, ‘complex’ conodonts. Previous modelling of element position and mechanical properties indicate they were capable of food processing. A direct test would be provided through evidence of in vivo element crown tissue damage or through in vivo incorporated chemical proxies for a shift in their trophic position during ontogeny. Here we focus on coniform elements from two conodont taxa, the phylogenetically primitive Proconodontus muelleri Miller, 1969 from the late Cambrian and the more derived Panderodus equicostatus Rhodes, 1954 from the Silurian. Proposing that this extremely small sample is, however, representative for these taxa, we aim to describe in detail the growth of an element from each of these taxa in order to the test the following hypotheses: (1) Panderodus and Proconodontus processed hard food, which led to damage of their elements consistent with prey capture function; and (2) both genera shifted towards higher trophic levels during ontogeny. We employed backscatter electron (BSE) imaging, energy-dispersive X-ray spectroscopy (EDX) and synchrotron radiation X-ray tomographic microscopy (SRXTM) to identify growth increments, wear and damage surfaces, and the Sr/Ca ratio in bioapatite as a proxy for the trophic position. Using these data, we can identify whether they exhibit determinate or indeterminate growth and whether both species followed linear or allometric growth dynamics. Growth increments (27 in Pa. equicostatus and 58 in Pr. muelleri ) were formed in bundles of 4–7 increments in Pa. equicostatus and 7–9 in Pr. muelleri . We interpret the bundles as analogous to Retzius periodicity in vertebrate teeth. Based on applied optimal resource allocation models, internal periodicity might explain indeterminate growth in both species. They also allow us to interpret the almost linear growth of both individuals as an indicator that there was no size-dependent increase in mortality in the ecosystems where they lived e.g ., as would be the case in the presence of larger predators. Our findings show that periodic growth was present in early conodonts and preceded tissue repair in response to wear and damage. We found no microwear and the Sr/Ca ratio, and therefore the trophic position, did not change substantially during the lifetimes of either individual. Trophic ecology of coniform conodonts differed from the predatory and/or scavenger lifestyle documented for “complex” conodonts. We propose that conodonts adapted their life histories to top-down controlled ecosystems during the Nekton Revolution.

Reconstructing the tectonic evolution of the southern Appalachian metamorphic internides is hampered by the relative paucity of accurate geochronologic constraints and the apparent rarity or absence of Paleozoic cover sequences. At the orogen’s greatest width, near the junction of Georgia, North Carolina, and Tennessee, the western Blue Ridge is a composite metamorphic allochthon of three major thrust sheets: (A) a basal sheet above the Great Smoky fault overlying rocks of the foreland thrust belt composed of the Lower Cambrian Chilhowee Group and underlying Sandsuck Formation of the Neoproterozoic Walden Creek Group; (B) an intermediate sheet above the Maggies Mill–Citico fault composed of the middle Paleozoic Maggies Mill Formation; and (C) the main mass of the western Blue Ridge above the Alaculsy Valley–Miller Cove fault composed of the Neoproterozoic Ocoee Supergroup, and younger overlying sequences in the Epperson and Murphy synclinoria. The age of peak deformation and metamorphism in all of these sequences has historically been assigned to the Ordovician Taconic orogeny, but recent paleontologic discoveries suggest these events are significantly younger. In addition to the middle Paleozoic fauna recently reported from the Maggies Mill Formation in the intermediate thrust sheet, Silurian-Devonian conodonts have been found in units formerly correlated with the Walden Creek Group in the Epperson synclinorium. These discoveries suggest that widespread middle Paleozoic successor basin sequences unconformably overlie the Neoproterozoic-Cambrian drift-facies of the Chilhowee Group (and equivalents) and underlying rift-facies of the Ocoee Supergroup, and require modifications to existing models for the timing of the region’s stratigraphic framework and tectono-metamorphic evolution.

With a record that spans approximately 300 million years (late Cambrian through the Triassic/Jurassic transition, i.e., the "Conodontozoic"), conodonts witnessed all principal events in the evolution of life on Earth, from the invasion of the land to the exploration of the air, from the explosion of biomineralization in the oceans to the rise of dinosaurs and mammals, including three of the major extinction events that occurred in the Phanerozoic. Mainly used for biostratigraphic or geochemical studies, the potential of conodonts to help unravel changes perceived to be of global extent rarely has been explored. While specialists have identified rapid changes in conodont element morphology throughout their history, the conodont animal has often been perceived to have been a static entity in a constantly evolving world, when biological equilibrium in the oceans was undergoing profound alteration and faunal recoveries took place in phases that seem to have had recurrent patterns. It is now essential that we begin to further investigate how conodonts, as biologic entities, responded to or were impacted by palaeogeographic changes, eustatic and climatic fluctuations, shifting redox conditions, and major faunal turnovers and reorganizations that took place during the "Conodontozoic".

The apparatus composition and architecture of prioniodinin conodonts is poorly understood, largely because few prioniodinin taxa are represented by articulated oral feeding apparatuses (natural assemblages) in the fossil record, but also due to the highly variable gradational morphology of their constituent elements that makes apparatus reconstruction problematic. We describe here a natural assemblage of Erismodus quadridactylus (Stauffer), a prioniodinin, from the Sandbian (Late Ordovician) of North Dakota, USA. The assemblage demonstrates that the apparatus architecture of Erismodus is similar to those of late Palaeozoic prioniodinins namely, Kladognathus Rexroad and Hibbardella Bassler, but also has similarities with ozarkodinin apparatuses. In addition, there is evidence to suggest that E. quadridactylus shares topological similarities to balognathid architecture, with respect to the position of its inferred P elements. The apparatus composition and architecture presented here indicate that, at least with respect to the M–S array, an ‘ozarkodinin‐type’ bauplan is probably more widely representative across prioniodontids. The assemblage demonstrates that element morphotypes traditionally considered to lie within the S array are M elements, whereas others traditionally interpreted as P elements are found in the S array. These observations are used as a basis for refining concepts of element homology among prioniodinin conodonts and their closest relatives.

The Fincastle Conglomerate is an Ordovician polymictic, poorly sorted, matrix-and clast-supported cobble to boulder-rich conglomerate located just north of Fincastle, Botetourt County, VA. At least nine other cobble and boulder conglomerates are located in a similar stratigraphic position from Virginia to Georgia west of the Blue Ridge structural front. All except the Fincastle are dominated (similar to 80%) by carbonate clasts; Fincastle clasts are much more varied and siliceous and it is this clast diversity that provides increased value for provenance and related studies. We have used a multidisciplinary approach that involves conodont analysis, sandstone petrography, in-situ outcrop clast characterization, optical petrography, electron-beam petrography and chemical analysis, and X-ray diffraction to provide data on lithologies, ages, and provenance. The size, roundness, and lithology of 1,656 clasts (> 1 cm) were measured in the field. Although, the clast lithology varies among the studied localities, the average lithology is sandstone and siltstone 12 %, vein quartz 17 %, limestone 31 %, low-grade quartzite/metasandstone 31 %, chert 6 %, and others 3 %. Dolomite, igneous, or high-grade metamorphic rock clasts were not identified in field study or in detailed laboratory analysis. Dolomite rhombs and authigenic albite feldspar were observed in some limestone clasts. Quantitative petrographic data for the Fincastle sandstone clasts indicate tectonic environments from passive margin to transitional continental uplift, but the conglomerate matrix modes have considerably less feldspar and plot in the foreland basin tectonic environment region. Proto-, para-, and euconodonts were identified from clast and matrix, but are long-ranging fauna indicating middle Cambrian to Middle or Late Ordovician ages; color alteration index (CAI) for euconodonts varied from 3 to 3.5. The occurrence of well-rounded clasts including limestone suggests a nearby, high-energy environment, and that transport was rapid enough to preserve limestone before deposition into a foreland basin. The lack of igneous or high-grade metamorphic rocks clasts suggests that the erosional level sampled by the Fincastle Conglomerate did not include the underlying Grenville basement of igneous or high-grade metamorphic rocks.

An integrated synthesis of existing datasets (detailed geologic mapping, geochronologic, paleontologic, geophysical) with new paleontologic and geochemical investigations of rocks previously interpreted as part of the Neoproterozoic Walden Creek Group in southeastern Tennessee suggest a necessary reevaluation of the kinematics and structural architecture of the Blue Ridge Foothills. The western Blue Ridge of Tennessee, North Carolina, and Georgia is composed of numerous northwest-directed early and late Paleozoic thrust sheets, which record pronounced variation in stratigraphic/structural architecture and timing of metamorphism. The detailed spatial, temporal, and kinematic relationships of these rocks have remained controversial. Two fault blocks that are structurally isolated between the Great Smoky and Miller Cove-Greenbrier thrust sheets, here designated the Maggies Mill and Citico thrust sheets, contain Late Ordovician-Devonian conodonts and stable isotope chemostratigraphic signatures consistent with a mid-Paleozoic age. Geochemical and paleontological analyses of Walden Creek Group rocks northwest and southeast of these two thrust sheets, however, are more consistent with a Late Neoproterozoic (550-545 Ma) depositional age. Consequently, the structural juxtaposition of mid-Paleozoic rocks within a demonstrably Neoproterozoic-Cambrian succession between the Great Smoky and Miller Cove-Greenbrier thrust sheets suggests that a simple foreland-propagating thrust sequence model is not applicable in the Blue Ridge Foothills. We propose that these younger rocks were deposited landward of the Ocoee Supergroup, and were subsequently plucked from the Great Smoky fault footwall as a horse, and breached through the Great Smoky thrust sheet during Alleghanian emplacement of that structure.