0000000000009809
AUTHOR
Bernard Laurin
Succession et remplacements de communautés à brachiopodes en régime de sédimentation discontinue (Jurassique Moyen, Bourgogne, France)
Abstract Sequence stratigraphy throws a new and seminal light on the fossil record and helps in determining the respective role played by external control (community replacement) and internal control (paleoecological succession) in the temporal “train” of marine benthic paleocommunities. Five brachiopod-dominated communities (C1–C5) are recognized and their temporal “train” described, during the uppermost Bathonian-lower Callovian interval in Burgundy. The first series (C1–C3) exhibits a trend interpreted as a paleoecological succession and the next two (C3–C4, C4–C5) as community replacements. Within the scope of sequence stratigraphy, the paleoecological succession comes at the end of a t…
Evolution of ammonoid morphospace during the Early Jurassic radiation
The morphologic radiation of Early Jurassic ammonites following the near extinction at the end of the Triassic is analyzed from 436 species of 156 genera that form a representative sample of morphs occurring worldwide in the first three stages of the Jurassic (Hettangian, Sinemurian, Pliensbachian: 36 subzones, 24 m.y.). Morphologic diversity is analyzed independently of taxonomy by processing 18 shape parameters using multivariate analysis and clustering techniques. The morphospace thus defined indicates that morphs fall readily into two groups made up of four and five adjacent morpho-subsets. The temporal pattern of morphospace occupation in the 36 Lower Jurassic subzones displays diversi…
La zonation du Jurassique Français par les Brachiopodes: Limites de résolution
Resume Deux successions de brachiopodes, calees sur la zonation standard d'ammonites, sont proposees, l'une pour ledomaine nord-tethysien, l'autre pour le domaine situe au sein des plates-formes de l'Europe moyenne. Cette distinction est rendue necessaire par les differences dans l'evolution paleogeographique et tectono-sedimentaire determinant les differents environnements. L'etablissement de ces echelles s'est heurte a un certain nombre de problemes, constituant des limites de resolution. Il s'agit de l'etat d'avancement inegal des etudes taxonomiques, de l'acception des especes et des genres, du choix des especes-indices de zone, des differences (meme a l'interieur d'un domaine paleogeog…
Hétérochronies, variabilité morphologiqueet tendances évolutives chez les brachiopodes jurassiques
Resume La lasticite morphologique d'un grand nombre d'especes de brachiopodes mesozoiques, notamment chez les rhynchonellides, est liee a la grande souplesse de leurs processus ontogenetiques. Elle s'exprime particulierement au niveau de la biconvexite des coquilles, par le jeu de trajectoires ontogenetiques multiples. Celles-ci peuvent se deduire les unes des autres en faisant intervenir des processus de type heterochronique. A l'echelle des tendances evolutives les modifications morphologiques sont en partie issues de processus similaires, associant etroitement paedo-et peramorphose. Leurs mecanismes ne peuvent etre correctement compris qu'a partir des donnees relatives aux modalites de l…
Heterochronic differentiation of sexual dimorphs among Jurassic ammonite species
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…
La notion d'espace morphologique,outil d'analyse de la morphodiversité des organismes
Resume L'analyse de la morphologie des organismes est une base essentielle dans la mise en evidence des changementsevolutifs. La morphologie est maintenant frequemment abordee par des procedures quantitatives, dont certaines permettent de construire de veritables cartes morphologiques ou les dissemblances et ressemblances de formes entre les organismes sont directement lisibles et quantifiees. La notion d'espace morphologique, illustree ici par differents exemples, se revele particulierement feconde pour comprendre comment la diversite morphologique d'un ensemble d'organismes (stades ontogenetiques, populations, clades) se structure, et par consequent pour interpreter en termes evolutifs ou…
Environmental and ontogenetic constraints on developmental stability in the spatangoid sea urchin Echinocardium (Echinoidea)
Biogeosciences, UMR-CNRS 5561, Universite de Bourgogne, 6 bd Gabriel, 21000 Dijon, FranceReceived 25 June 2004; accepted for publication 25 July 2005Spatangoid irregular sea urchins are detritivorous benthic organisms particularly prone to variations of environ-ment, and their mode of growth and plate morphology make them an appropriate model to assess the effects of envi-ronmental variations. Two populations of Echinocardium flavescens were sampled in two sites of the Norwegiancoast characterized by contrasted environmental conditions. Different morphological descriptors (plate areas, inter-landmarks distances, overall size, and shape of the posterior ambulacra) were used to appraise interi…
The recovery and radiation of Early Jurassic ammonoids: morphologic versus palaeobiogeographical patterns
Abstract The recovery and radiation of the Early Jurassic ammonoid morphospace, as represented by nine morphologic groups identified in an earlier study, are traced through the first 36 subzones of the Hettangian to Domerian time interval. A quantitative survey of the dispersion of 436 species over 15 palaeogeographical areas reveals seven palaeobiogeographical patterns, each corresponding to an exclusive set of species exhibiting similar characteristics in terms of distribution and abundance. This study combines morphologic, chronostratigraphical, and palaeobiogeographical data in an attempt to investigate possible connections between morphologic recovery and radiation patterns and the his…
L'ontogenèse complexe du spatangue Echinocardium cordatum: Un test des standards des trajectoires hétérochroniques
The growth of the spatangoid echinoid Echinocardium cordatum is described by using the three standards (size,shape and age) that are classicaly involved in analyses of heterochronies. A population from Normandy, including all the growth stages, allows an ontogenetic reference to be established, while comparisons are performed with adult samples from other localities (Brittany, Aquitaine, and New-Zealand). The morphology of E. cordatum is characterized by 23 measured parameters and 13 calculated indexes. The ontogenetic trajectory of the species is depicted from the measurements of the size increments, from the analysis of the shape changes, and from an estimate of age. An estimate of the ag…
Morphological and genetic analyses reveal a cryptic species complex in the echinoid Echinocardium cordatum and rule out a stabilizing selection explanation.
14 pages; International audience; Preliminary analyses revealed the presence of at least five mitochondrial clades within the widespread sea urchin Echinocardium cordatum (Spatangoida). In this study, we analyzed the genetic (two mitochondrial and two nuclear sequence loci) and morphological characteristics (20 indices) from worldwide samples of this taxon to establish the species limits, morphological diversity and differentiation. Co-occurring spatangoid species were also analyzed with mitochondrial DNA. The nuclear sequences confirm that mitochondrial lineages correspond to true genetic entities and reveal that two clades (named A and B1) hybridize in their sympatry area, although a more…
Morphometrics and Cladistics: Measuring Phylogeny in the Sea Urchin Echinocardium
A phylogenetic approach to the study of evolutionary patterns is based on taxic homologies (synapomorphies). In contrast, the recognition of evolutionary processes (namely heterochronies) involves analysis of the entire morphology. Recent developments in geometric morphometry permit analysis of morphological similarities grounded in operational homologies. Such morphometric techniques are explored (1) at the level of evolutionary processes, and (2) as a complement in exploration of phylogenetic relationships. To examplify this, we perform a two-part study of the ontogeny and phylogeny of the spatangoid sea urchin Echinocardium. First, a phylogenetic analysis of ten Recent species in the gen…
Quantification of cranial convergences in arvicolids (Rodentia)
Cranial convergence in nine species of arvicolids is quantified phenetically using geometric morphometry. In a preliminary step, a hypothesis about phyletic relationships is proposed as a framework against which to examine morphological comparisons. The cranial morphology is then depicted in three series of 37, 20 and 13 landmarks characterizing the lower, upper and lateral sides of the skull respectively. Superimposition (Procrustes) methods are used to quantify shape differences and establish phenograms for the three sides of the skull. The phenogram obtained for lateral sides reveals a strong connection between skull profile and mode of life: surface dwelling forms have elongated skulls …
Modèles morphométriquesen paléontologie évolutive
Resume La mise en evidence des changements evolutifs est longtemps restee fondee sur des appreciations qualitatives des differences morphologiques. Puis la formulation du concept d'espece biologique a suscite des approches populationnelles et quantitatives. Cependant les demarches classiques font appel a des mesures lineaires qui ne donnent qu'une image approchee de la forme et de ses changements. Pour repondre aux besoins de quantification et de modelisation de la forme des organismes, deux autres types de modeles sont presentes: 1) des modeles analogiques qui s'appuient sur des parametres mathematiques generant des representations geometriques analogues aux formes des organismes; 2) des m…
Environmental and ontogenetic constraints on developmental stability in the spatangoid sea urchin Echinocardium (Echinoidea).
13 pages; International audience; Spatangoid irregular sea urchins are detritivorous benthic organisms particularly prone to variations of environment, and their mode of growth and plate morphology make them an appropriate model to assess the effects of environmental variations. Two populations of Echinocardium flavescens were sampled in two sites of the Norwegian coast characterized by contrasted environmental conditions. Different morphological descriptors (plate areas, interlandmarks distances, overall size, and shape of the posterior ambulacra) were used to appraise interindividual variations, and fluctuating asymmetry. The comparisons were carried out using classical fluctuating asymme…