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Conodont elements have high rates of morphological evolution, but the drivers of this disparity are debated. Positive allometric relationships between dimensions of food-processing surfaces and entire P1 elements have been used to argue that these elements performed mechanical digestion. If involved in food processing, the surface of the element should grow at a rate proportional to the increase in energy requirements of the animal. This inference of function relies on the assumption that the energy requirements of the animal grew faster (≅ mass0.75) than the tooth area (≅ mass0.67). We reevaluate this assumption based on metabolic rates across animals and calculate the allometry in platform-bearing P1 elements of Late Triassic co-occurring taxa, Metapolygnathus communisti and Epigondolella rigoi , using 3D models of ontogenetic series. Positive allometry is found in platform and element dimensions in both species, supporting a grasping-tooth hypothesis, based on the assumption that metabolic rate in conodonts scaled with body mass similarly to that in fish and ectotherms. We also calculate the curvature of the P1 platform surface using the Dirichlet normal energy (DNE) as a proxy for diet. DNE values increase with body mass, supporting the assumption that conodont metabolic rates increased faster than mass0.67. We finally find that adults in both taxa differ in their food bases, which supports trophic diversification as an important driver of the remarkable disparity of conodont elements. [ABSTRACT FROM AUTHOR]

The early Palaeozoic biodiversification is the most significant radiation of marine ecosystems of Earth’s history, starting with the appearance of invertebrate organisms near the Precambrian–Cambrian boundary and followed by a significant diversification during the Great Ordovician Biodiversification Event (GOBE). The apparently sudden appearance of major phyla of metazoans during the earliest Cambrian (i.e., the ‘Cambrian Explosion’, c.a. 540 Ma) has been considered by many as corresponding to an ‘explosive’ process that took place during a very short time interval. Similarly, the GOBE has been considered as a short spectacular global event triggering a massive biodiversification during the early Middle Ordovician (c.a. 470 Ma). However, it appears that both ‘events’ have been more intensively studied in a few locations, creating multiple gaps, and thus a bias, in the biodiversity datasets. For example, the ‘Furongian gap’ (late Cambrian) is clearly an artefact in the Paleobiology Database (PBDB), which includes mostly data from North America and Western Europe. These geographic areas were more intensively sampled and recorded in the PBDB than others (e.g., China), separating the ‘Cambrian Explosion’ and the GOBE artificially, whereas the Geobiology Database (GBDB), which is focused on data from eastern Asia, records a more gradual increase of the global diversity during the early Palaeozoic. These diversity curves are indeed not truly global but reflect patchy data from different palaeocontinental margins. Moreover, the evolution of global biodiversity is mostly estimated only in two dimensions (taxonomic richness versus time) and spatial distribution is rarely assessed. The organisms might have occupied the Earth’s surface heterogeneously because of constraints on their ecological niches, generating ‘diversity hotspots’ that were recorded in some databases and not in others. We want to test whether global ‘explosions’ of diversity ever occurred, or instead a single, but very complex, long-term evolutionary process took place over space and time, starting in the late Precambrian and lasting throughout most of the early Palaeozoic, with changing ‘diversity hotspots’ at different palaeogeographical locations. To do so, we use echinoderms as a model and we propose a protocol to (1) assess the validity of diversity curves based on data currently available online, and (2) analyse the spatio-temporal evolution of their diversity (i.e., generic richness) in the Cambrian and the Ordovician. We first compare echinoderms diversity curves between the PBDB, the GBDB and an original database built from a comprehensive synthesis of the literature, with a temporal resolution at the scale of the stratigraphic stage. Then, we gather the three datasets to build a synthetic database that includes a revised taxonomy. To avoid fake spatio-temporal diversity peaks and hotspots, we define comparable stratigraphic units in terms of temporal range and gather sampled sections that refer to the same locality (e.g., the Montagne Noire). We will present the comparison of the diversity curves between the three databases and the details of the whole methodological protocol. [ABSTRACT FROM AUTHOR]

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.