Pascal Neige

University of Burgundy | UB · Unité Mixte de Recherche Biogéosciences

A comprehensive phylogenetic hypothesis for Devonian phacopid trilobites of the genus Austerops has not previously been proposed. We carried out a cladistic analysis of the 13 species and subspecies assigned to Austerops, based on a data matrix of 63 characters. Two species of the morphologically very similar genus Chotecops, C. auspex and C. hoseri, and seven other close relatives (Reedops cephalotes hamlagdadianus, Boeckops stelcki, Morocops granulops, Paciphacops logani, Phacops latifrons, Phacops araw and Pedinopariops (Hypsipariops) vagabundus) were also included in the analysis in order to test their relationship with species of Austerops. Parsimony analyses using a heuristic method, with Calyptaulax callirachis and C. glabella as outgroup taxa, produced two most parsimonious trees of 341 steps. These trees are partly consistent with trees obtained from additional analyses performed with modified data sets (deletion of homoplastic characters, multistate characters, continuous characters carved into 5% increments, thoracic and pygidial characters, or taxa with numerous unknown characters). Results suggest that Austerops sp. B and A.? sp. D are close to Chotecops hoseri and C. auspex, and that these species constitute a monophyletic group. Austerops Austerops menchikoffi, A. speculator and A. punctatus are also a monophyletic group and reasonably constitute a sister group of that formed by the rest of Austerops and Chotecops sensu lato, while A. hottonensis seems phylogenetically distant from other representatives of Austerops. Chotecops including C. hoseri and C. auspex together with Austerops sp. B and A.? sp. D seem derived from A. legrandi. The relationship between Austerops and Chotecops remains partly unresolved but it seems likely that their recognition as separate taxa results in paraphyletic groups. The phylogenetic analysis suggests that the currently poorly known Austerops sp. B and A.? sp. D should be reassigned to Chotecops.

[This corrects the article DOI: 10.1371/journal.pone.0194575.].

Evolutionary radiations are fascinating phenomena corresponding to a dramatic diversification of taxa and a burst of cladogenesis over short periods of time. Most evolutionary radiations have long been regarded as adaptive but this has seldom been demonstrated with large-scale comparative datasets including fossil data. Originating in the Early Jurassic, irregular echinoids are emblematic of the spectacular diversification of mobile marine faunas during the Mesozoic Marine Revolution. They diversified as they colonized various habitats, and now constitute the main component of echinoid fauna in modern seas. The evolutionary radiation of irregular echinoids has long been considered as adaptive but this hypothesis has never been tested. In the present work we analyze the evolution of echinoid species richness and morphological disparity over 37 million years based on an extensive fossil dataset. Our results demonstrate that morphological and functional diversifications in certain clades of irregular echinoids were exceptionally high compared to other clades and that they were associated with the evolution of new modes of life and so can be defined as adaptive radiations. The role played by ecological opportunities in the diversification of these clades was critical, with the evolution of the infaunal mode of life promoting the adaptive radiation of irregular echinoids.

Dataset of echinoid occurrence records. Occurrence records of the 664 fossil species of echinoids recorded worldwide for the eight geological stages of the studied time period based on the literature [72, 73, 74, 75]. Type species names are in bold. First Appearance Datum (FAD) and Last Appearance Datum (LAD) given in million of years Before Present (after Gradstein et al. [71]). References are the source data used for morphometric analyses. (XLSX)

Dataset of landmark and semi-landmark coordinates. Coordinates of landmarks (LM) and semi-landmarks (SLM) used to depict ambitus and peristome outlines of each species. (XLSX)

Morphological space detailed for each echinoid clade. All specimens of echinoid are plotted in light grey along the first two components of the PCA (see Fig 4). The respective specimens of each clade are highlighted in dark (regular clades) or in color (irregular clades). (EPS)

Compared total diversity and disparity values for each clade. Plot of morphological disparity expressed as the Mean Pairwise Distance (MPD) against taxonomic diversity in number of species for the studied time interval. Poly: Polycidaridae, Cid: Cidaridae, Aulo: Aulodonts, Hemi: Hemicidaridae, Ps: Pseudodiadematidae, Cal: Calycina, Ech: Echinacea, Orth: Orthopsidae, Eo: Eognathostomata, Deso: Desorellidae, Neo: Neognathostomata, Atelo: Atelostomata. (EPS)

Morphological space of echinoid disparity plotted for each geological stage. For each stage, only species occurring at that time period are plotted in the PCA. (EPS)

Testing for the significance of disparity differences. To test for the significance of differences in disparity between clades null distribution models were computed for each clade and each time interval following the method developed by Losos and Miles [21] and Neige et al. [18]. The measured disparity values expressed as Mean Pairewise Distances (MPD) were compared to the range of null distribution values (grey bars) to test whether they can be considered unusually high (grey circles) or low (open circles). No test was performed for clades with less than five species per time period. Poly: Polycidaridae, Cid: Cidaridae, Aulo: Aulodonts, Hemi: Hemicidaridae, Ps: Pseudodiadematidae, Cal: Calycina, Ech: Echinacea, Orth: Orthopsidae, Eo: Eognathostomata, Deso: Desorellidae, Neo: Neognathostomata, Atelo: Atelostomata. (EPS)

Echinoid disparity and diversity detailed for each clade and each geological stage. Grey shaded bars of histograms show diversity values expressed as species richness for each geological stage (left axis, in number of species). Red curves show disparity values expressed as Mean Pairwise Distance for each geological stage (right axis). Error bars correspond to 95% confidence intervals computed by bootstrapping (500 replicates). Ages in million of years Before Present (after Gradstein et al. [71]). (EPS)

http://sciencepress.mnhn.fr/sites/default/files/articles/pdf/g2018v40a4.pdf. The present paper deals with the systematic description of the belemnite assemblages from the Lower Jurassic, collected at the Roche Blain quarry, Fresney-le-Puceux. In spite of the reduced thickness of the succession at Fresney-le-Puceux, 13 successive ammonite chronozones could be documented in this rather unique outcrop situation in mainland Europe. Twelve genera and 26 species of belemnites belonging to the Passaloteuthididae, Hastitidae, Megateuthididae, Salpingoteuthididae, and family incertae sedis are described and illustrated herein. The stratigraphical range of the belemnites is correlated with the standard ammonite zonation, using the chronozone concept: the described specimens range from the lower Pliensbachian (Davoei Chronozone) to the uppermost Toarcian (Aalensis Chronozone) while ammonites indicate the Aalenian (Murchisonae Chronozone) to be present too, but these beds delivered no identifiable belemnites so far. The belemnite diversity from Normandy is compared to data from coeval outcrops in Western and Central Europe.

Des abysses aux sommets, embarquez pour un voyage extraordinaire à la rencontre des merveilles de la Nature! Depuis 4 milliards d'années, l'évolution ne cesse d'inventer des formes et des modes de vie qui surprennent et qui font la biodiversité actuelle. Ce livre vous fait découvrir 101 espèces animales et végétales, parfois disparues, parmi les plus insolites que la Nature ait conçues. Chaque espèce est présentée en double page, associant une spectaculaire image et un texte explicatif. Plongez dans ce livre et laissez-vous guider à la rencontre de ces 101 merveilles de l'évolution qu'il faut avoir vues dans sa vie!

New coleoid cephalopods are described from statolith remains from the Middle Eocene (Middle Lutetian) of the Paris Basin. Fifteen fossil statoliths are identified and assigned to the Sepiidae (Sepia boletzkyi sp. nov.,? Sepia pira sp. nov.), Loliginidae (Loligo clarkei sp. nov.), and Ommastrephidae (genus indet.) families. The sediments containing these fossils indicate permanent aquatic settings in the infralittoral domain. These sediments range in age from 46 Mya to 43 Mya. Analysis of the fossil record of statoliths (from findings described here, together with a review of previously published data) indicates marked biases in our knowledge. Fossil statoliths are known from as far back as the Early Jurassic (199.3 to 190.8 Mya) but surprisingly, to the best of our knowledge, no record occurs in the Cretaceous. This is a “knowledge bias” and clearly calls for further studies. Finally, we attempt to compare findings described here with fossils previously used to constrain divergence and/or diversification ages of some coleoid subclades in molecular phylogenies. This comparison clearly indicates that the new records detailed here will challenge some estimated divergence times of coleoid cephalopod subclades.

In this chapter, we shall explore a variety of cases of evolutionary radiations in the fossil record. The case studies are chosen for their exemplary value. The Cambrian explosion over 500 million years ago is striking because of the emergence of a particularly diversified abundance of life. The ammonites – a clade that lived for over 350 million years – are a good example of the degree of biodiversity that can be achieved in terms of successive diversifications. The radiation of flowering plants, at the start of the Cretaceous a little over 120 million years ago, is an essential example of delayed anatomical invention in terms of geological time, followed by a major diversification in the plant kingdom. Finally, non-rounded sea urchins show us that the loss of a feature may prove beneficial. This took place at the start of the Jurassic, around -190 million years ago.

Amellago, Morocco, January 2001. After 3 days trekking through the mountains of the Moroccan high atlas, a French/Moroccan team of paleontologists and geologists, of which I was a member, reached a rich outcrop of fossils. Amongst the fossils we found seven specimens of ammonites. These marine cephalopod mollusks are easily identifiable by their spiral, chambered shell. They date from the lower Jurassic – a period of Earth’s history ranging between 201 and 145 million years ago. The ammonite shells collected are recognizable by the morphological features. In the present case, some of them were particularly striking: the lack of a keel, the presence of significant constrictions and thin ribs, a very round-shaped cross-section, or a particularly sinuous suture line (the line at the meeting point of the shell and the internal walls). Although the individuals were not all absolutely identical (exhibiting a few minor morphological variations), I considered them all to belong to the same fossil species: a species of the genus Alocolytoceras (the genus is the level in the biological nomenclature just below the species; thus a genus covers several species), known at the end of the lower Jurassic and the start of the mid Jurassic. In scientific language, this species is known as Alocolytoceras coarctatum.

An evolutionary radiation is a rapid increase in the diversity of a clade. The diversity of the clade is generally measured by a taxonomic value (the number of species, genera, etc.). This diversification indicates a very positive balance between the number of apparitions and the number of extinctions of taxa within the clade. At a time t + 1, there will be more taxa than at time t. During the course of an evolutionary radiation, this balance very rapidly becomes highly positive, in comparison to the evolutionary patterns that we usually observe.

The history of biodiversity on the planet Earth could be compared to a work of theater. Biodiversity is a word which has been on the lips of many, often with a note of concern in the speaker’s voice. Yet what is biodiversity? The word simply denotes the variety of biological organisms. When you walk through a forest, when you dive into the sea, when you roam through a wheat field, relax on the beach or trek through a desert, you can see this biodiversity all around you. Almost by definition, it is not identical everywhere: sometimes ubiquitous, sometimes more discrete, but always present on (or near) the surface of our planet and in the oceans. It has been this way for a long time. For billions of years, even. Thus, biodiversity has a history – a very long one. In order to correctly and accurately analyze this biodiversity, it is necessary to look at its historical aspect, in context. With over 270,000 recorded species, flowering plants are, indubitably, a major part of the biodiversity present in the world today – all the more so when one considers that practically all vegetable material that we use in human foodstuffs comes from flowering plants. How come they are so diverse? When did this situation arise? Without understanding their diversification over the eons through geological records, we have no hope of accurately grasping the extent, nature and significance of their diversity today.

An evolutionary trend is a pattern of traits shifting in a given direction over a sufficiently long period of time to be detected. In this study, we examine trends among Jurassic ammonoids. First, a compilation of selected literature on evolutionary patterns and trends leads to the conclusion that such trends have rarely been studied among Jurassic ammonoids and even more rarely are they formally studied using statistical tests. Second, a preliminary survey of trends for the entire Jurassic at the family level (based on four published articles) suggests two sustained trends occurred each lasting nearly 10 myr: the Early Jurassic and Middle Jurassic radiations, which were related to the first-order End-Triassic Extinction and to the second-order Early Toarcian Crisis, respectively. Finally, we discuss factors that may be responsible for the scarcity of proven trends among Jurassic ammonoids.

The fossil record offers a surprising image: that of evolutionary radiations characterized by intense increases in cash or by the sudden diversification of a single species group, while others stagnate or die out. In a modern world, science carries an often pessimistic message, surrounded by studies of global warming and its effects, extinction crisis, emerging diseases and invasive species. This book fuels frequent "optimism" of the sudden increase in biodiversity by exploring this natural phenomenon. Events of Increased Biodiversity: Evolutionary Radiations in the Fossil Record explores this natural phenomenon of adaptive radiation including its effect on the increase in biodiversity events, their contribution to the changes and limitations in the fossil record, and examines the links between ecology and paleontology's study of radiation.

A gastropod fauna has been studied from upper Pliensbachian – upper Toarcian deposits of two sections of the Causses Basin (southern France) in order to investigate the mode of recovery after the early Toarcian anoxic event. The fauna consists of 15 species, one of which is new (Bathrotomaria kronzwilmesorum sp. nov.). Their stratigraphical distribution shows two peaks of diversity – in the Bifrons Zone (Bifrons Subzone) and in the Aalensis Zone (Mactra Subzone) – which reflect brief times during which the oxygen content and bottom consistency favoured the settlement of a relatively diversified fauna. In the Variabilis–Pseudoradiosa zones, gastropods are only represented by two species. This probably indicates more severe and unstable environmental conditions, only allowing the survival of gastropod taxa with wide adaptive capacities. The very low species diversity and the discontinuous and slow faunal recovery were probably determined by physiographic factors. The Causses area was a small basin confined by exposed lands and open towards the central part of western Tethys. Gastropods described here occur exclusively in the Toarcian – early Aalenian communities of the European epicontinental seas, whereas species from the central region of western Tethys are absent. Geographic isolation and marginal location of the Causses Basin restricted faunal exchange with the western European epicontinental seas, preventing fast recovery after the anoxic event. Gastropods of the central region of the western Tethys were probably unable to settle and colonize that area due to the strongly different environment.

Belemnites (Belemnitida) played a major role in marine ecosystems at Jurassic and Cretaceous times. Their fossil record suggests a successful diversification already during the Early Jurassic, with a peak during the Toarcian. The aim of this study is to explore the radiation of belemnites at the scale of the western Tethys, and adjacent areas, from the Hettangian to the Aalenian. A comprehensive bibliographic research and original material study allowed obtaining a signal of species diversity and exploring, using statistics and rarefaction techniques, the potential relation between belemnites diversity and the biogeography trough the studied time interval. However, our research reveals that data for Early Jurassic belemnites are largely concentrated in Toarcian and on north-western Europe (Germany, Great Britain, Luxembourg, etc.) whereas little is known from the rest of the Europe (Causses and Quercy Basins, Provence Platform, northern Spain, etc.), and from the Mediterranean areas (Italy, Austria, Southern Spain, North Africa, etc.). In these latter areas and especially for the beginning of the Early Jurassic, data are still dramatically low, and what is known about belemnites is whether old and without any figuration or sparse. This state of facts blurs our perception of the real radiation of belemnites during the Early Jurassic. In order to increase the knowledge in these areas and periods it is necessary to acquire new data. Thus, belemnites appear to us as a rewarding group for future field research, each field campaign being able to significantly improve our knowledge of the belemnites radiation and palaeobiogeography.

Jurassic belemnites represent promising proxies especially for palaeoecological and also paleobiogeographical reconstructions. However, basic knowledge on taxonomic composition, biostratigraphy and diversity of Lower Jurassic belemnites is still dramatically low, especially for France. The present study provides new data on belemnites from the southern part of the Northwest European Province. More than 700 specimens have been collected along the Tournadous section in the Causses Basin (Southern France); they represent ten genera and 30 species belonging to Hastitidae, Megateuthididae, Passaloteuthididae and Salpingoteuthididae. Furthermore, numerous ammonites have been collected, allowing to establish a standard chronostratigraphical scheme and thus to assign, for the first time, a precise stratigraphical distribution to the Lower Jurassic belemnites of Southern France. The analysis of belemnites diversity and its variations along the section, compared to the well-known fauna of the northern part of the Northwest European province (Germany and England), opens interesting prospective for belemnite palaeobiogeography.

Evolutionary radiations have been extensively studied especially in the fossil record and in the context of postcrisis recoveries. The concept of adaptive radiation that emerges from this very broad topic explicitly involves the effect of adaptation driven by ecological opportunity and is considered to be of the foremost importance. It is essential to be able to detect adaptive radiation because it points up factors that predispose a clade to radiate. Adaptive radiation has received much attention in recent decades based mostly on studies dealing with recent clades, but data from the fossil record are still scarce. This study begins to fill this gap with the example of Lower Jurassic ammonoids (through c. 8 Myr of history). A survey of several clades, using both taxonomic and disparity-based approaches, shows that they diversified successively through time, but not systematically, in terms of species numbers and morphological variety. Some clades seem to have exhibited adaptive radiation and to have become rapidly extinct. One clade (which engendered nearly all post–Lower Jurassic ammonoids) has a fossil record that begins with low diversity and disparity but is superseded by a sustained radiation pattern. The results are discussed in the light of the Modern Synthesis and its continuation into an Extended Evolutionary Synthesis.

We devised a simple model for assessing the role of development in shaping the evolution of morphological disparity. Disparity of a clade at any given time is expressed in terms of the developmental dynamics that lead to the variety of adult morphotypes observed. We use assumed phenotypic manifestations of developmental processes, as they could be detected from allometric characterizations, to distinguish a few, nonexclusive types of evolutionary changes in ontogeny. On the basis of this formalization, we describe the diversification of hypothetical clades, using the standard curve of adult morphological disparity, the curve of juvenile disparity, and the curve of allometric disparity, the latter quantifying the diversification of clades in allometric space. Contrasts of these curves reflect the underlying developmental scheme that drives temporal changes in disparity. We then vary the parameters of the model to assess the expected signature of each metric under specific conditions: changes in the relative frequencies of the types of evolutionary developmental changes, changes in the transition magnitude attached to each of them, and effects of temporal variation in average adult size on disparity curves and patterns of morphospace occupation. Results emphasize the potential contribution of these proxies for developmental dynamics—juvenile morphological disparity, allometric disparity, and average adult size—in enriching the interpretation of standard disparity curves and the description of clade histories, with possible process-oriented inferences.

The explosive ammonoid rediversification after the Permian–Triassic mass extinction is now well understood in terms of taxonomic richness and biogeography. using an updated dataset of Early Triassic ammonoids, we compare morphological disparity and taxonomic richness patterns at the regional and global scales. Disparity evolved similarly at both scales, suggesting a global influence of abiotic factors. Morphological diversification occurred early in the Smithian and a marked contraction of the morphospace took place during the end-Smithian extinction. We confirm that trends in disparity and richness were decoupled during the Griesbachian and Dienerian. Three macroevolutionary processes may be involved: (1) a nonselective extinction at the Permian–Triassic boundary; (2) a Dienerian constrained radiation with several homeomorphic genera; (3) a potential deterministic extinction during the end-Smithian crisis. We also demonstrate a superfamily imprint upon disparity for the Spathian when most superfamilies occupied a restricted part of the morphospace. Sphaerocones were the most affected by the Dienerian and end-Smithian extinction, but explanations remain elusive. On the one hand, this may be linked to widespread harsh conditions at those times. On the other hand, as the sphaerocones occurred episodically during the Early Triassic, this might be explained by a relaxing of ecological constraints or simply by convergent evolution.

This paper illustrates the potentialities of a home-made portable LIBS (laser-induced breakdown spectroscopy) instrument in Earth sciences, more particularly in geochemically recognizing (i) tephra layers in lacustrine sed-iments and (ii) fossilization processes in ammonites. Abundances for selected lines of Al, Ca, Fe, Ti, Ba and Na were determined in lacustrine chalk sediments of the Jura, where the Laacher See Tephra (LST) layer is recorded. A statistical treatment of elemental maps produced from the section of a sedimentary column containing the LST event allows instrumental conditions to be optimized. Accumulating spectra from close shot positions gives better results than multiplying shots at the same location. A depth profile method was applied to study ammo-nite fossilization (pyritization, phosphatization) processes. Depth variations of Fe, Ca, Al intensities, and Fe/Ca and Al/Ca ratios provide indications about pyritization, but phosphatization processes cannot be determined with our device.

Conservation biologists and palaeontologists are increasingly investigating the phylogenetic distribution of extinctions and its evolutionary consequences. However, the dearth of palaeontological studies on that subject and the lack of methodological consensus hamper our understanding of that major evolutionary phenomenon. Here we address this issue by (i) reviewing the approaches used to quantify the phylogenetic selectivity of extinctions and extinction risks; (ii) investigating with a high-resolution dataset whether extinctions and survivals were phylogenetically clustered among early Pliensbachian (Early Jurassic) ammonites; (iii) exploring the phylogenetic and temporal maintenance of this signal. We found that ammonite extinctions were significantly clumped phylogenetically, a pattern that prevailed throughout the 6.6 Myr-long early Pliensbachian interval. Such a phylogenetic conservatism did not alter--or may even have promoted--the evolutionary success of this major cephalopod clade. However, the comparison of phylogenetic autocorrelation among studies remains problematic because the notion of phylogenetic conservatism is scale-dependent and the intensity of the signal is sensitive to temporal resolution. We recommend a combined use of Moran's I, Pearson's ϕ and Fritz and Purvis' D statistics because they highlight different facets of the phylogenetic pattern of extinctions and/or survivals.

Ammonite phylogenetic trees for the 3 chronozones and 10 subchronozones of the early Pliensbachian. Species in red are those becoming extinct during the interval. (PDF)

Moran's I and Pearson's ϕ correlograms for the 10 subchronozones of early Pliensbachian. In each graph the grey line corresponds to the upper 95% limit of the null model. (PDF)

Application of Moran's I to extinction and survival patterns. A: Simple theoretical phylogenetic hypothesis for five species (A–E), among which species A and B become extinct in a same time interval (daggers); B: Vector corresponding to the coding of either extinctions or survivals as used by the Moran's I. Note that only this vector differs between extinctions and survivals, the W matrix is the same; C: Moran's I will take the same value for both survivals and extinctions due to the mathematical properties of this index. Similarly, Moran's I could not distinguish this pattern of extinction from one in which species C, D and E would become extinct although the phylogenetic distance between extinct species differ. (PDF)

The Pliensbachian–Toarcian crisis (Early Jurassic) is one of the major Mesozoic paleoecological disturbances when ca. 20% of marine and continental families went extinct. Contemporaneously, profound paleobiogeo-graphical changes occurred in most oceanic domains including a disruption of ammonite provincialism during the Early Toarcian. Here, we quantitatively reappraise the structure and evolution of paleobiogeographical patterns displayed by ammonite faunas before, during, and after the biological crisis, over a time-interval including 13 biochronozones. The high-resolution study presented here involves the use of hierarchical Cluster Analyses, non-metric Multi-Dimensional Scaling methods, and Bootstrap Spanning Network approaches that we apply to a large database including 772 ammonite species from 16 northwestern Tethyan and Arctic basins. Our results confirm a robust faunal dichotomy between Euro-Boreal and Mediterranean areas throughout the Pliensbachian, with the first emergence of an Arctic biome during the cooling regressive event of the Spinatum Zone. Whatever its complexity, Pliensbachian provincialism could be directly linked to paleogeographical barriers and to latitudinal paleoclimatic and paleoecological contrasts. During the Early Toarcian, this pattern was progressively lost, with northward expansions of Mediterranean ammonites during the Tenuicostatum Zone, followed by a strong interprovincial mixing during the Falciferum Zone. This faunal homogenization results from the combination of several parameters including a major sea-level rise facilitating basinal connections, a global warming event stretching the spatial range limits of southern taxa, and a mass extinction preferentially removing endemic species. Ammonite provincialism, although slightly different, was progressively re-established during the cooling regressive trend of the Middle Toarcian. These results therefore suggest a paramount influence of paleoclimatic, eustatic, and extinction constraints on the paleobiogeography of Early Jurassic ammonites, even if some threshold effects or independent biological factors may sporadically complicate the patterns.

The Pliensbachian–Toarcian interval was marked by major environmental disturbances and by a second-order mass extinction. Here, we reappraise the taxonomic, spatiotemporal and selective dynamics of extinctions over the whole interval, by analysing a high-resolution dataset of 772 ammonite species from NW Tethyan and Arctic domains. On average, 40–65% of ammonite species disappeared during each subchronozone, but higher extinction pulses (reaching 70–90%) prevailed from the Margaritatus to the Dispansum Chronozone. The main extinctions, corresponding to the Gibbosus, Pliensbachian–Toarcian boundary, Semicelatum, Bifrons–Variabilis, and Dispansum events, differed in their dynamics, suggesting episodes of ecological stress related to climate change, regression, disturbance in the carbon cycle or anoxia. The multi-pulsed volcanic activity in the Karoo–Ferrar province could well have triggered these ecological changes. In addition, ammonites experienced a morphological bottleneck during the Gibbosus event, 1 Ma before the Early Toarcian diversity collapse. Typically, drops in richness were related both to high extinctions and to declines in origination rates. This feature could result from strengthened ecological stresses related to the temporal overlap of environmental disturbances. After the Early Toarcian crisis, the recovery of ammonites was rapid (2 Ma) and probably influenced by a coeval marine transgression.

We compare 110 Spirula shells from five geographical areas. Morphometry provides a criterion for determining when shell growth ends (decrease in whorl height). Characteristics of adult shells apparently vary with geographical origin: specimens from Madagascar, New Zealand and Brazil are larger than those from North-West Africa and Australia. These findings challenge the monospecific status of the genus Spirula but fall short of proving the occurrence of more than one species. Supplementary molecular investigations are called for.

Résumé Les ammonoïdes qui perdurent 335 Ma constituent un modèle de choix dans l'analyse du fait évolutif. Cet article de synthèse se propose d'aborder (1) : leur place phylogénétique au sein des céphalopodes et le choix d'un modèle actuel de référence ; (2) : la construction d'espaces phénotypiques qui offrent un angle d'étude pertinent de l'évolution biologique ; (3) : les concordances et discordances entre reconstruction phylogénétique et registre fossile et (4) : les reconquêtes postcrises, modèles d'étude de l'évolution à grande échelle. Il ressort que les ammonoïdes peuvent servir d'appui à de nombreuses thématiques paléontologiques (dynamique de la biodiversité, analyse phylogénétique, analyse du registre fossile) qui permettent et qui permettront encore de mieux cerner l'évolution biologique, notamment dans un contexte d'étude à grande échelle. Pour citer cet article : P. Neige et al., C. R. Palevol 8 (2009). © 2008 Académie des sciences. Publié par Elsevier Masson SAS. Tous droits réservés.

A set of published, unpublished, and new clay mineral data from 60 European and Mediterranean localities allows us to test the reliability of clay minerals as palaeoclimatic proxies for the Pliensbachian–Toarcian period (Early Jurassic) by reconstructing spatial and temporal variations of detrital fluxes at the ammonite biochronozone resolution. In order to discuss their palaeoclimatic meaning, a compilation of low-latitude belemnite δ18O, δ13C, Mg/Ca, and 87Sr/86Sr values is presented for the first time for the whole Pliensbachian–Toarcian period. Once diagenetic and authigenic biases have been identified and ruled out, kaolinite content variation is considered as a reliable palaeoclimatic proxy for the Early Jurassic. Major kaolinite enrichments occur during times of low δ18O, high Mg/Ca, and increasing 87Sr/86Sr, implying warm climates and efficient runoffs during the Davoei, Falciferum and Bifrons Zones. Conversely, cooler and drier times such as the Late Pliensbachian or the Late Toarcian are characterized by low hydrolysis of landmasses, and correspond to kaolinite depleted intervals. Secondary factors as modifications of sources or hydrothermalism may sporadically disturb the palaeoclimatic signal (e.g., in the Bakony area during the Late Pliensbachian). In addition, a spatial comparison of clay assemblages displays significant kaolinite enrichments towards northern parts of the Peritethyan Realm, probably related to the latitudinal zonation of hydrolyzing conditions. This implies enhanced runoffs on northern continental landmasses that reworked kaolinite-rich sediments from subtropical soils and/or Palaeozoic substrata.

For decades, theoretical morphological studies of different groups of organisms have been successfully pursued in biological, paleontological, and computational contexts, often with distinct modeling approaches and research questions. A regular influx of new perspectives and varied expertise has contributed to the emergence of a veritable multidisciplinary outlook for the-oretical morphology. The broadening of this discipline is reflected in a substantial increase in the number of models, leading to a bewildering diversity that has yet to be scrutinized. In this work, we tackle this issue in a synthetic fashion, with a quantitative meta-analysis that allows an objective comparison of theoretical morphological models treated as entities. By analogy with empirical morphospace analyses of actual organisms, we performed a multivariate ordination of a represen-tative sample of models, producing a metaspace of models in which patterns of similarity and dif-ference are visualized. A phenetic tree was used to characterize the relationships between models. Four major groups have been identified, and their disparity analyzed. We suggest this typology as a useful starting point to identify a core set of fundamental principles and protocols for better interpretation of the plethora of current models and for more efficient construction of models in the future. This in turn can help in diversifying the scope of macroevolutionary, developmental, and bioenvironmental questions in theoretical morphology.

Here, we advance novel uses of allometric spaces--multidimensional spaces specifically defined by allometric coefficients--with the goal of investigating the focal role of development in shaping the evolution of morphological disparity. From their examination, operational measures of allometric disparity can be derived, complementing standard signals of morphological disparity through an intuitive and process-oriented refinement of established analytical protocols used in disparity studies. Allometric spaces thereby become a promising context to reveal different patterns of evolutionary developmental changes and to assess their relative prevalence and importance. Such spaces offer a novel domain of investigation of phenotypic variation and should help in detecting large-scale trends, thus placing various macroevolutionary phenomena in an explicitly developmental context. Ammonoidea (Cephalopoda) at the Lower-Middle Jurassic transition were chosen as a case study to illustrate this methodological approach. We constructed two phenotypic spaces: a static, adult one (adult morphospace) and a dynamic, developmental one (allometric space). Comparative disparity analyses show a strikingly stable occupation in both spaces, despite extensive change in taxonomic composition. In contrast, disparity analyses of subclades reveal clearly distinct morphological and allometric disparity dynamics. Allometric approaches allow developmental insights into morphological diversification otherwise intractable from the analysis of adult morphospace alone.

The ammonite genus Alocolytoceras Hyatt, 1900 is an uncommon lytoceratid with distinctive shell ornament. A set of 58 specimens, recently collected at Amellago in the central High Atlas (Morocco), has enabled us to trace a succession of three species over eight biozones from the Toarcian to the Aalenian. Two specimens from the Lusitanian Basin are added for comparison. Following a review of the genus, based on original specimens and data from the literature, seven species are considered valid. A palaeobiogeographical synthesis of 13 regions demonstrates irregular distribution patterns over time, with a constant presence in the south-west Tethys and an instance of rapid diversification of an endemic fauna in north-west Europe. Our data challenge the conventional view that lytoceratid ammonite evolution was ‘conservative'.

This work is dedicated to the study of the rich ammonite faunas of the Pliensbachian and early Toarcian of the Roche Blain quarry (Calvados, France). About fifty Pliensbachian species have been collected in this fossiliferous locality. They are distributed in a dozen of distinct levels. Faunas are sometimes condensed. All the collected species are described (at least concisely) and illustrated. Some delicate traits like peristomes and/or subtle details of the shell surface are sometimes preserved. Excepted two taxa (Arieticeras cf. amalthei (OPPEL, 1853) and Dactylioceras (Eodactylites) sp.) clearly affiliated with the Tethyan (Mediterranean) faunas, all the ammonites collected in the Roche Blain quarry are obviously connected with the north-west European palaeobiogeographical province. A number of the Pliensbachian ammonite assemblages of the Roche Blain quarry are noticeably more varied than those observed in the most part of the north-west European localities. It is especially surprising to discover two obviously new ammonites species (Acanthopleuroceras gauthieri nov. sp DOMMERGUES & MEISTER et Catriceras (?) rioulti nov. sp. DOMMERGUES & MEISTER) in a single quarry. Indeed, the ammonite faunas of the Anglo-Parisian basins are extensively documented. Moreover the Pliensbachian faunas of the Roche Blain quarry include many specimens which are difficult to attribute without doubt to a genus and/or to a species previously described in the literature. These fairly numerous more or less ambiguous forms enhance to the peculiarity of the Pliensbachian faunas of the Roche Blain quarry. The diversity of these faunas is probably partly related with the unusual paleogeographical framework. During the Pliensbachian, the area corresponding with the extant "Campagnes" of Caen and of Falaise, was characterised by a intricate framework of reefs, shallows, furrows and rather small basins. Various biotopes and numerous refuges were thus available in a relatively small area. Besides, this region close to the NE coasts of the Armorican landmass was a palaeogeographic crossroads widely open towards various deeper and/or more subsiding parts of the Anglo-Parisian basins. Faunal exchanges were probably possible as well as with the basins of the western part of the English Channel (e.g., Dorset) than with the Paris basin.

Two major research themes in Evolutionary Developmental Biology and in Paleobiology, respectively, have each become central for the analysis and interpretation of morphological changes in evolution: the study of ontogeny/phylogeny connections, mainly within the widespread and controversial framework of heterochrony; and the study of morphological disparity, the morphological signal of biodiversity, describing secular changes in morphospace occupation during the history of any given clade. Although enriching in their respective fields, these two themes have remained rather isolated to date, despite the potential value of integrating them as some recent studies begin to suggest. Here, we explore the recent notion of developmental morphospace-morphospace carrying ontogenetic information-as a potential tool for bridging the gap between disparity dynamics and developmental dynamics. We elaborate this approach with a case study of Early Jurassic ammonite family Hildoceratidae (Mollusca, Cephalopoda). Morphometric analyses of the shell shape of 20 species spanning the morphological spectrum of the family are used to quantify and contrast juvenile and adult disparity levels. Adult disparity is significantly greater than juvenile disparity at the family level; yet, some subclades also display different patterns. In addition, comparisons of ontogenetic trajectories underline the prevalence of heterochrony-based evolutionary modifications within subfamilies (via ontogenetic scaling); they also point to the probable existence of pervasive developmental constraints structuring inhomogeneous morphospace occupation.

The Middle Jurassic ammonite radiation (from the late Aalenian to the end of the mid-Bathonian) is traced using combined analyses of morphological disparity and taxonomic diversity. The global signals of disparity and diversity are compared. These signals are then broken down by paleogeographical provinces to detect any heterogeneity in the radiation. An examination of the global signals reveals three biodiversity crises (discordances between signals) where morphological disparity grows while taxonomic diversity declines. The subdivision of the signals indicates the radiation was heterogeneous between provinces: the global signal is an aggregate of signals from each province. The three biological crises have different paleogeographical signatures: the first is visible in a few provinces only while the other two are visible in most provinces. First-order crises can be distinguished from second-order ones by studying the number of paleogeographical provinces affected.

Ontogenetic and then heterochronic approaches are used here to analyze sexual differentiation within two well-known Jurassic dimorphic species. This analysis compares two ways of determining the relative biological age of ammonites, one using size (diameter) and the other the number of septa as a proxy of age. The shape standard is established from factor analysis of morphological and growth parameters. Size-age-shape relationships are analyzed on the basis of a new heterochronic representation. When diameter is used as a proxy of age, microconch morphs are globally considered to be progenetic compared with macroconch morphs. When size and age are determined separately and shape is included, (1) Ebrayiceras jactatum (microconch morph) has a shorter period of growth (progenesis) with acceleration of shape compared with its macroconch morph (Morphoceras macrescens), (2)(Cardioceras cordatum (microconch morph) has a shorter period of growth (progenesis) coupled with a slower rhythm of growth (dwarfism) compared with its macroconch morph. These findings emphasize the complex relationship between supposed sexual dimorphs in ammonites when size and age standards can be separated, as well as the need for an ontogenetic approach.

One of the most popular activities among paleontologists is to attribute species names to fossil specimens and then to classify species in a hierarchical pattern: the so-called Linnaean classification. This taxonomic activity is vital, ensuring a large corpus of knowledge of past life across geological times. By-products are: the study of biodiversity through time, the discovery of some extraordinary events such as mass extinctions and major radiations, and the slicing of geological time into singular associations of fossils (known as biozones) to date sediments.

Cuttlefishes exhibit several hard structures that have been charac-terised using morphometric analysis. Most of these data come from cuttlebones, al-though statoliths and beaks are also used. It appears that morphometric techniques are mainly used for taxonomic purposes. However, some analyses have emphasised functional morphology and macroevolution. Morphological features (including the inner shell) of cuttlefishes and their availability for study (numerous specimens, culture in the laboratory) make them a first rank model for numerous studies in life sciences that require morphometrics, and especially in the field of evolutionary bi-ology.

Multivariate analysis of shell characters and quantification of morphological diversity (morphospace occupation and disparity) are used here to investigate the modes of morphological diversification of ammonites. We define five events in early cardioceratid history that connect geo-graphical changes causing emigration or immigration phases with biodiversity dynamics: (1) the initial colonization of the Arctic Basin by the Cardioceratidae at the end of the Bajocian, Middle Jurassic; (2) the first appearance of the Kosmoceratidae clade in the Boreal Realm during the Bath-onian; (3) the ensuing expansion phase of this clade in the Boreal Realm; (4) the first phase of migration of the Cardioceratidae (early Callovian) through Eastern Europe, Western Britain and the Yukon corridor; and (5) the second unrelated migration phase in the Western Interior only. Analysis of spatial occupation shows that acquisition of this field occurs essentially by replacement or subdivision of preexisting peaks of occupation. These replacements seem to follow different patterns: progressive trend, saturation, iteration, and apparent preferential extinction. We describe these patterns and suggest different factors that may have shaped them, including a morphological differentiation that has been interpreted by various authors as sexual dimorphism. Another factor that could cause disparity modification is fluctuations in the ammonites' proximal environment. The effect of immigrating faunas is a third (and preponderant) factor that is prominent in the stud-ied example: immigration phases of the Cardioceratidae lead to increased morphological diversity, whereas the spread of nonindigenous species reduces it and is contemporaneous with a morpho-logical shift in the native clade. We thus demonstrate here that geographical constraints play a significant role in the expression of innovation and may be seen as a major factor in macroevolu-tionary dynamics.

The exploration of evolutionary patterns over geological time has recently received new impetus from the development of morphological disparity as a new biodiversity metric alongside taxonomic diversity. Clade dynamics can be analyzed by comparing and contrasting these two metrics. Like any metrics based on sampling, quantification, and naming, taxonomic diversity and morphological disparity are not free from bias. The long use of taxonomic diversity has prompted many studies of bias and its effects, whereas bias affecting morphological disparity has only been summarily explored. This is particularly so for the effect of the growth of knowledge over paleontographical time (i.e., historical period of study) and its repercussions on morphological disparity and on the relative stability of disparity and diversity. Here, we analyze evolutionary patterns at a detailed scale. For a sample of Jurassic ammonites, morphological disparity increases faster than taxonomic diversity during paleontographical time. For disparity, we demonstrate two paleontological practices, based on comparison with a random numerical model: a tendency to identify and name extreme forms before intermediate ones for some morphological aspects (ornamentation), and a correlated tendency to underuse some other morphological aspects (shell geometry). However, the effects of the growth of knowledge over paleontographical time are only slightly marked on biodiversity curves through geological time, mainly because new discoveries and revalidations and/or invalidations of species are randomly distributed within the subzones during paleontographical time.

Résumé. – Les paléontologues disposent de la morphologie des restes fossilisés pour proposer des hypothèses phylogé-nétiques et de la succession stratigraphique des taxons pour placer ces hypothèses dans le contexte temporel. Chez les ammonites, dont l'enregistrement fossile est réputé de haute qualité, les auteurs ont cependant eu tendance à privilégier le rôle des données stratigraphiques dans les reconstructions phylogénétiques ; la morphologie n'intervenant que pour séparer des lignées contemporaines. Cette pratique s'est largement développée au cours du temps et prévaut encore au-jourd'hui. Il n'en demeure pas moins que les méthodes employées pour proposer des hypothèses phylogénétiques sont relativement éclectiques. En effet, (1) le degré d'intégration des données morphologiques et stratigraphiques varie en fonction de l'auteur et (2) les arbres phylogénétiques proposés dépendent toujours de concepts évolutifs qui varient se-lon les écoles. Il en résulte que les relations phylogénétiques qui sont fondées sur ces méthodes éclectiques, même si el-les peuvent être jugées raisonnables, présentent des faiblesses théoriques et pratiques. Plus récemment, des auteurs ont montré que la méthode cladistique peut offrir une alternative opérationnelle pour la reconstruction de la phylogénie de ce groupe. Ammonites phylogenetic analysis: state of the art and new prospects Abstract. – Two main types of data are available to resolve phylogenies using fossils data: (1) stratigraphic ordering of taxa, and (2) morphological characters. In most phylogenetic studies dealing with ammonites, authors have given priority to the stratigraphic distribution of taxa. This practice is classically justified by the fact that the ammonite fossil record is frequently outstandingly good. In practice, the level of integration of stratigraphic and morphologic information in a single analysis depends on the confidence that authors have in the quality of data. Besides, many evolutionary concepts, which could differ over time and between authors (e.g. anagenesis, cladogenesis, iterative evolution), are added to these data to help infer phylogenetic relationships. As a result, phylogenetic hypotheses are based on eclectic methods which depend on the relative weight given to stratigraphic and morphologic information as well as on evolutionary concepts used. The vali-dity of relationships proposed by previous authors is not dealt with in this paper. Instead, our goal is to draw attention to problems that these eclectic methods may cause, that is to say: (1) ammonites systematics is poorly formalised and (2) phylogenetic hypotheses as they are classically constructed are not rigorously testable. During the last 10 years, cladistic analysis has been applied to ammonites but is still unpopular among ammonitologists. However, studies have consistently shown that cladistics is not as unsuited a tool for ammonites phylogenetic reconstruction as is widely believed. Moreover, classical works open new questions about ammonite phylogeny and in particular, help to reappraise our view on the defini-tion of morphological characters and their phylogenetic significance.

A new faunal assemblage of six ammonite species is described. It comes from the Domerian beds (Margaritatus zone, Subnodosus subzone, Gloriosus horizon) of the section of Água de Maderios (São Pedro de Muel, Portugal). This assemblage is constituted on one hand by typical NW European species belonging to the genus Tragophylloceras, Amaltheus and Amauroceras and on the other hand by two new species. These later are probably closely related and are perhaps a micro-macroconch pair. They are tentatively attributed to the sub-genus Fieldingiceras. One of these new forms is here described as Fuciniceras capilliolusitanicum nov. sp. It is characterized by an extremely thin falciradiate ribbing and by a more or less roof shaped ventral area. These Fuciniceras possibly are a new illustration of ammonite species restricted to the Lusitanian Basin.

This paper studies the very first Lusitanian ammonites. These late Sinemurian (Obtusum Zone) forms are found in two distinctly marly layers within the mainly calcareous "Coimbra Beds s.s." which crop out north of São Pedro de Muel (Portugal). These ammonites are endemic taxa belonging to the groups Ptycharietites ptychogenos (Pompeckj) and Ptycharietites muellense nov. sp. They exhibit such highly derived morphologies that they cannot be likened to any other genus of the related Asteroceratinae subfamily. Paedomorphic spreading of smooth, involute, platycone morphologies is a very unusual process within the Asteroceratinae in particular and within the Arietitidae in general. Until now the groups of P. ptychogenos (Pompeckj) and of P. muellense nov. sp. have only been reported in the northern part of the Lusitanian basin and do not seem to have any palaeogeographical affinities with the adjacent NW European or Tethyan faunas. The first appearance of the genus Ptycharietites in the Lusitanian basin was a sudden event. It could be interpreted as a punctuated evolutionary event or as a faunal ingression from some undetermined origin. In fact, as the Lusitanian basin has the only onshore outcrops for the whole Central North Atlantic area, origination in one or more undocumented neighbouring offshore basins is the more plausible hypothesis.

Two samples of ammonoids belonging to the Oppeliidae, Sublunuloceras virguloidesHecticoceras (Brightii) canaliculatum, are analyzed to estimate the intraspecific variability of embryonic shell features. The study of embryonic shell characters reveals two main shapes of protoconch, flattened and round. Prosiphons may be straight or slightly curved. New parameters for area are added to the linear parameters commonly found in the literature. Prosiphon length and caecum area vary greatly whereas protoconch and ammonitella diameter vary only slightly, and the ammonitella angle is almost constant. The protoconch-to-ammonitella size ratio behaves differently in each species, suggesting different patterns of embryonic growth. We compare our results with published data and discuss their significance for species determination and ontogenetic interpretation. The main finding is that intraspecific embryonic variation is greater than was previously believed.

Reçu le 19 mai 2003 ; accepté le 17 septembre 2003 Rédigé à l'invitation du Comité éditorial Résumé La théorie macroévolutive est abordée sous des aspects historiques, puis sous un de ses aspects plus novateurs, qui aboutit à l'élaboration d'un programme de recherche initié par différentes équipes depuis une dizaine d'années : il consiste à découpler les composantes taxinomiques (diversité) et morphologiques (disparité) de la biodiversité, lors de l'étude de ses fluctuations. Plusieurs études suggèrent des découplages temporels fréquents entre ces deux métriques au cours de l'histoire des clades. La confrontation des deux apparaît comme une démarche féconde qui a permis d'explorer en termes de patterns, mais également de processus, les fluctuations de la biodiversité à large échelle. Pour citer cet article : P. Neige, C.R. Palevol 2 (2003). © 2003 Académie des sciences. Publié par Éditions scientifiques et médicales Elsevier SAS. Tous droits réservés. Abstract The macroevolutionary debate. Several historical as well as more recent aspects of macroevolutionary theory are discussed, in connection with a research program initiated by several working groups over the last ten years: it consists in dividing the taxonomic (diversity) and morphologic (disparity) components of biodiversity when studying its fluctuations through time. Studies have frequently shown a dissociation between the two metrics through the history of clades. Comparing diversity and disparity is a productive approach, which is leading to an exploration of large-scale biodiversity fluctuations in terms of both patterns and processes. To cite this article: P. Neige, C.R. Palevol 2 (2003). © 2003 Académie des sciences. Publié par Éditions scientifiques et médicales Elsevier SAS. Tous droits réservés.

Aim Diversity and disparity metrics of all Recent cuttlefishes are studied at the macroevolutionary scale (1) to establish the geographical biodiversity patterns of these cephalopods at the species level and (2) to explore the relationships between these two metrics. Location Sampling uses what is known about these tropical, subtropical and warm temperate cephalopods of the Old World based on a literature review and on measurements of museum specimens. Some 111 species spread across seventeen biogeographical areas serve as basic units for exploring diversity and disparity metrics in space. Methods Landmarks describe the shape of the cuttlebone (the inner shell of the sepiids) and differences between shapes are quantified using relative warp analyses. Relative warps are thus used as the morphological axis for constructing morphospaces whose characteristics are described by disparity indices: total variance, range, and minimum and maximum of relative warps. These are analysed and then compared with the diversity (species richness) metric. Results Results show no significant latitudinal or longitudinal gradients either for diversity or for disparity. Around the coast of southern Africa, disparity is high regardless of whether diversity (species richness) is high or low. In the ‘East Indies’ area disparity is low despite the high diversity. Main conclusions The relationship between diversity and disparity is clearly not linear and no simple adjustment models seem to fit. The number of species in a given area does not predict its disparity level. The particular pattern of southern Africa may be the result of paleogeographical changes since the Eocene, whereas that of the ‘East Indies’ may indicate that this area could act as a centre of origin. However, the lack of any clear phylogenetical hypothesis precludes the study from providing any explanation of the observed patterns.

The genera usually considered into the Bouleiceratinae subfamily belong in fact to different lineages of the Hildoceratidae family. An approach using paleogeographical, stratigraphical and morphological arguments on one hand and a cladistic approach on the other hand have allowed to separate 3 clusters with different paleogeographical and stratigraphical localisations. These are: •the Bouleiceratinae s.s. (genera Bouleiceras, Nejdia and Kohaticeras) from lower Toarcian;•the Leukadiellinae (genera Leukadiella and Renziceras) from middle Toarcian;•and the Paroniceratinae (genera Frechiella, Paroniceras and Oxyparoniceras) from middle and upper Toarcian. These latters are mainly present and the Tethyan domain, but are also known in the NW of Europe and especially in France where new populations have been studied in the Causses, in the centre-ouest and in the Lyon area. New taxa have been erected here: Oxyparoniceras (Neoparoniceras) nov. sub. gen., O. (N.) brocardi nov. sp. and O. (N.) sciaui nov. sp.

Diversity and disparity metrics of recent cuttlefishes are studied at the macroevolutionary scale to establish the geographical biodiversity patterns of these cephalopods at species level and to explore the relationship between these two metrics. One hundred and eleven species distributed in 17 biogeographic areas serve as basic units to explore these complementary biodiversity metrics in space. Landmarks describe cuttlebones; differences between shapes are quantified using relative warp analyses. Relative warps are used as the morphological axis to construct morphospaces whose characteristics are described with total variance as a disparity index. Disparity is analysed and then compared with diversity (i.e. species richness). Results show the peculiarity of southern African coasts (high disparity level with low or high species richness) and the low disparity level of the "East Indies" area associated with high species richness. The particular pattern of southern Africa may have been caused by paleogeographical changes since the Eocene whereas that of the "East Indies" may indicate that this area could have acted as a centre of origin. The number of species in a given area does not predict the level of disparity, which suggests the need for both diversity and disparity metrics to be explored when studying biogeography.

The shell size of 1236 ammonite species representing all known Early Jurassic faunas is analyzed. Size patterns are studied for the entire period and then at the biozone scale for the first four stages of the Jurassic (28 Myr), during which ammonites recovered from the crisis at the Tri-assic/Jurassic (T/J) boundary. Our analysis reveals that (1) a size continuum (normal distribution from ''dwarfs'' to ''giants'') exists for all Early Jurassic ammonites; (2) although there are no sus-tained trends (e.g., no Cope's rule), the succession is not monotonous and patterns may differ con-spicuously from one biozone to the next; and (3) increases and decreases in size range are the most frequent evolutionary styles of size change. The only pattern that can be connected with a particular episode of Early Jurassic ammonite history is the initial increase in size disparity during the first four biozones attributable to phyletic radiation after the T/J crisis. Subsequent correlations with environmental constraints (e.g., sea-level changes), although suspected, cannot be shown.

Toarcian ammonites from Chantonnay (Vendée, France): palaeontological analysis, biostratigraphy and reflection on the Hildoceratinae. Toarcian ammonites from the Chantonnay section (Vendée, France) are analyzed (taxonomy and biostratigraphy). This section supplements a nearby one published by Gabilly (1976a, b). Shape variability and evolutionary patterns of species of the genus Hildoceras Hyatt, 1867 are discussed and compared with the faunas described here. Previously published phylogenetic reconstitutions for the Hildoceratinae are analyzed and criticized. It appears that authors use both morphological and stratigraphic arguments when attempting phylogenetic reconstitutions. We suggest that it would be preferable to base phylogenetic reconstitutions on morphological arguments alone. © Publications Scientifiques du Muséum national d'Histoire naturelle, Paris.

Morphological changes observed in ammonites at the Lias - Dogger (Toarcian - Aalenian) boundary are analyzed here. The study covers all known ammonites worldwide over some 2 m.y. (the last two biozones of the Toarcian : Pseudoradiosa and Aalensis and the first biozone of the Aalenian : Opalinum). Ammonite taxonomy at this boundary is still open to question, the main disagreements being over groupings at family or super-family level. The evolutionary schema developed by Tintant and Mouterde [1981] shows two main sets of Ammonitina for the time : (1) the dominant Hammatocerataceae (Graphoceratidae + Hammatoceratidae) and (2) the final representatives of the Hildocerataceae. Two conservative ammonite stocks coexisted alongside these Ammonitina : Phylloceratina and Lytoceratina. The ammonites under review are those that made the transition from the ≪typically Liassic stock≫ to the ≪post-Liassic stock≫ prefiguring all subsequent Jurassic ammonites. A morphometric procedure is used to quantify ammonite morphological disparity rather than taxonomic diversity. A set of 35 characters were considered, corresponding to the end of the phragmocone and to the body chamber. We selected 64 morphologies covering the entire range of shapes found at the subzone scale. Morphological disparity is expressed graphically by morphospaces (first factorial plane of correspondence analysis) and arithmetically by a space occupation index (sum of variances on the factor axes). The FAD and LAD of the selected species allow us to study morphospace changes at the subzone scale. The results clearly show changes occurring in the course of the seven subzones. The earliest subzone (Levesquei) has points weakly grouped around two poles (negative and positive F1 values) with an isolated point characterized by a very negative F2 value. Changes in this morphospace from the Pseudoradiosa subzone to the Lugdunensis subzone are marked by increased dispersion around the two poles. By contrast, an increasing number of morphologies have clearly negative F2 values. The Lias - Dogger boundary displays further dispersion of the two morphological poles, leading to them becoming indistinct. Continuation after the boundary shows a very similar pattern with shapes scattered and covering most of the morphospace. The morphospace changes analyzed previously were quantified by the sum of variances of the first 15 factorial axes, representing more than 90% of the information contained in the original matrix. For the Ammonoidea as a whole, the poorest coverage of the morphospace occurred in the Levesquei subzone, while the best coverage occurred in the Comptum and Bifidatum subzones. Between-times, morphological disparity increased at varying rates with no drastic changes at the Lias - Dogger boundary. A similar procedure was performed for the Ammonitina only. Indeed, the occurrence of two conservative sets (Lytoceratina and Phylloceratina) could be suspected of inducing - at least initially - two peculiar morphological poles and introducing a bias into the quantification. The results are similar, bringing out more clearly the increase in morphological disparity at the end of the Lias, and its stagnation thereafter. It is difficult to say why morphological disparity increased as it did. The main problem is the lack of any clearly resolved phylogeny for the ammonites under study. However, if we accept the hypothesis of Tintant and Mouterde [1981] recognizing five homogeneous clusters for ammonites of these times, it can be seen that two of them alone (Graphoceratidae first, and Hammatoceratidae later) account for the increased disparity. Within this phylogenetic assumption, it is improbable that external constraints alone, such as eustasy or physico-chemical phenomena, could have brought about the increase, for they would probably have affected all of the ammonoids, or at least the three Ammonitina groups that were initially quite similar in shape (in the Levesquei sub-zone). It is more likely then that internal factors (e.g. heterochrony) leading to two consecutives biological ≪explosions≫ (Graphoceratidae and Hammatoceratidae) were instrumental in bringing about this increased disparity. Finally, if the Lias - Dogger boundary is clearly marked by changes at any taxonomic level, our results - based on a quantification of morphological disparity and not on taxonomy - show that changes in ammonites can only be properly understood in a broader context : there was some morphological change at the Lias - Dogger boundary but it was initiated at the beginning of the Pseudoradiosa subzone. The Lias - Dogger event was thus not an unusual or major one, but more the end of a sustained event initiated two zones earlier. This period of time (final two zones of the Toarcian) witnessed progressive growth in disparity, which ceased only at the beginning of the Dogger.

This paper reports on a pilot study using, for the first time, a Procrustes type analysis of shape in exploring the morphospace of cephalopod statoliths. A total of 12 species of cuttlefish and squid (Decabrachia) from the Mediterranean were analyzed, based on 18 homologous points (landmarks) chosen on the anterior statolith surface. For two species (one cuttlefish, one loliginid squid) size ranges were sufficiently large to reveal ontogenetic trends in statolith. Comparisons between species resulted in four well-defined sets of statolith morphology corresponding, respectively, to (1) sepiid cuttlefish, (2) Rossia (a large sepiolid squid), (3) myopsid squids, (4) oegopsid squids and small sepiolids. The morphological "dissociation" of large and small sepiolids suggests a relation between statolith size and shape "distinctness," and draws attention to the possibly paedomorphic shapes at the lower end of the size scale.

In the Dijon area, the top of the Athleta zone contains rich ammonite fauna dominated quantitatively by two families: Perisphinctidae and Oppeliidae. The Oppeliidae are diversified and make up a numerically larger proportion of the ammonite fauna than in the underlying strata (up to 57 %). The exceptional state of preservation of the ammonites has permitted a precise study to be made of ontogenesis and intraspecific variability. Four sub-families are found (Oppeliinae, Hecticoceratinae, Distichoceratinae and Taramelliceratinae), within which sexual dimorphs have been recognised. One small form, characterized by lappets and a body chamber with ellipticoidal-trending coiling, is interpreted as the microconch dimorph of the Paralcidia genus which was unknown until now. One specimen of Creniceras, the oldest collected in Côte-d'Or, can be interpreted as the microconch dimorph of Taramelliceras.

The use of landmarks and geometrical morphometric techniques is illustrated with examples from the Harpoceratinae (Ammonitina). This approach is useful in analysing morphological variations of characters such as rib pattern or ventral shape on the scale of the genus or species. It can be used to map forms so that similarities and dissimilarities between organisms can be read and quantified directly.

The examination of more than 25 ammonite taxa and their biostratigraphic succession in an exceptionally complete and fossiliferous section near Rich in the Central High Atlas Mountains (Morocco) indicates there are 10 basic biochronological units (=assemblages) for a period extending from the end of the Early Sinemurian to the Late Sinemurian. These are the most precise biostratigraphical data so far collected in North Africa for the Oxynotum and Racicostatum zones. The many newly acquired data for the Early Sinemurian and Obtusum zone complete and/or confirm an initial horizon scale recently proposed for the Béni-Mellal area of the High Atlas Mountains. Some 25 per cent of the forms identified in this paper are new and one species, Asteroceras langi nov. sp., is described. The regional distinctiveness of the fauna, which is very marked throughout the period under consideration, makes correlation with other Mediterranean regions difficult and more difficult still with North Western Europe. Consequently the widely accepted subzone scale cannot be used. Quantified analysis of morphologies shows a correlation between shell coiling patterns and variations in argillaceous supply.

The examination of more than 25 ammonite taxa and their biostratigraphic succession in an exceptionally complete and fossiliferous section near Rich in the Central High Atlas Mountains (Morocco) indicates there are 10 basic biochronological units (= assemblages) for a period extending from the end of the Early Sinemurian to the Late Sinemurian. These are the most precise biostratigraphical data so far collected in North Africa for the Oxynotum and Raricostatum zones. The many newly acquired data for the Early Sinemurian and Obtusum zone complete and/or confirm an initial horizon scale recently proposed for the Béni-Mellal area of the High Atlas Mountains. Some 25 per cent of the forms identified in this paper are new and one species, Asteroceras langi nov. sp., is described. The regional distinctiveness of the fauna, which is very marked throughout the period under consideration, makes correlation with other Mediterranean regions difficult and more difficult still with North Western Europe. Consequently the widely accepted subzone scale cannot be used. Quantified analysis of morphologies shows a correlation between shell coiling patterns and variations in argillaceous supply.

Analysis of organism morphology is essential for highlighting evolutionary changes. Morphology is now frequently investigated using quantitative procedures, some of which can be used to produce morphological maps from which differences and similarities in shape between organisms can be read and quantified directly. The concept of morphological space, as illustrated here by different examples, is especially useful for understanding how the morphological diversity of a set of organisms (ontogenetic stages, populations, clades) is structured and consequently for interpreting shape changes in terms of evolution or adaptation.

The pyritized fossil-bearing marls of the Jura (Lower Oxfordian) contain an ammonite that is remarkable because of its tiny adult size (less than 16 mm) and of the scaphitoidal coiling of its body chamber, which is similar to that of certain Cretaceous Scaphitaceae. Anatomical and ontogenetic analysis demonstrates that these individuals, which are ascribed to Scaphitodites scaphitoides (Coquand, 1853), formed a single species. We argue that the genus Scaphitodites derived from Taramelliceras by a complex process of progenesis (sensu Landman et al., 1991).

The morphological diversity, considered as a biological signal, of a series of four Upper Callovian (Middle Jurassic) ammonite populations of Côte-d’Or (France) is quantified. These populations fall within two third-order sequences of a second-order transgression. A sampling method that adheres as closely as possible to the morphological characteristics of the populations is established. It is valuable in that it eliminates the subjectivity related to taxonomy to allow more objective comparisons between the biological signal (shell morphology) and the physical signal (eustasy).

The morphological diversity, considered as a biological signal, of a series of four Upper Callovian (Middle Jurassic) ammonite populations of Côte-d'Or (France) is quantified. These popula-tions fall within two third-order sequences of a second-order transgression. A sampling method that adheres as closely as possible to the morphological characteristics of the populations is established. It is valuable in that it eliminates the subjectivity related to taxonomy to allow more objective comparisons between the biological signal (shell morphology) and the physi-cal signal (eustasy).

Analysis of organism morphology is essential for highlighting evolutionary changes. Morphology is now frequently investigated using quantitative procedures, some of which can be used to produce morphological maps from which differences and similarities in shape between organisms can be read and quantified directly. The concept of morphological space, as illustrated here by different examples, is especially useful for understanding how the morphological diversity of a set of organisms (ontogenetic stages, populations, clades) is structured and consequently for interpreting shape changes in terms of evolution or adaptation.

The complete ontogenetic development (protoconch to adult) of Creniceras renggeri (Oppel) is reconstructed by morphometrical studies of its shell (protoconch, ammonitella, whorl expansion rate, whorl height, siphuncle, septal spacing, crenulation and adult size). The embryonic stage is equated with eggdevelopment. Hatching occurred at about 568 μm (end of ammonitella) where probably only two septa were secreted. No larval stage is assumed. Post-embryonic development exhibits no drastic morphological changes. This is interpreted as a constant mode of life from hatching to sexual maturity.

The rib shape of Harpoceratinae (Protogrammoceras and Fuciniceras) from Morocco are analyzed by identifying homologous points and are then compared with an equivalent fauna from Italy. Morphological similarities and differences between taxa are evaluated by LSTRA and baseline adjustment methods. Both methods reveal numerous morphological convergences while emphasizing the distinctive morphology of some Moroccan taxa. The methods prove effective for comparing fauna from different regions.

A rich ammonite fauna from Lower Oxfordian (Cordatum zone, lower part of Cordatum subzone) was collected at Zalas (Poland). This fauna yields numerous specimens of Euaspidoceras Spath and Mirosphinctes Schindewolf. Comparative analysis shows a lot of similarities in the inner whorls. From these data, they are considered in this paper as macroconch (Euaspidoceras) and microconch (Mirosphinctes) from a single palaeobiospecies. Compared ontogenesis with an heterochronic point of view, using the age, the size and the shape, shows that the microconch is dwarf and progenetic. -English summary

Two samples of ammonoids belonging to the Oppeliidae, Sublunuloceras virguloides and Hecticoceras (Brightii) canaliculatum, are analyzed to estimate the intraspecific variability of embryonic shell features. The study of embryonic shell characters reveals two main shapes of protoconch, flattened and round. Prosiphons may be straight or slightly curved. New parameters for area are added to the linear parameters commonly found in the literature. Prosiphon length and caecum area vary greatly whereas protoconch and ammonitella diameter vary only slightly, and the ammonitella angle is almost constant. The protoconch-to-ammonitella size ratio behaves differently in each species, suggesting different patterns of embryonic growth. We compare our results with published data and discuss their significance for species determination and ontogenetic interpretation. The main finding is that intraspecific embryonic variation is greater than was previously believed.