The shell matrix and microstructure of the Ram's Horn squid: Molecular and structural characterization.

Molluscs are one of the most diversified phyla among metazoans. Most of them produce an external calcified shell, resulting from the secretory activity of a specialized epithelium of the calcifying mantle. This biomineralization process is controlled by a set of extracellular macromolecules, the organic matrix. In spite of several studies, these components are mainly known for bivalves and gastropods. In the present study, we investigated the physical and biochemical properties of the internal planispiral shell of the Ram's Horn squid Spirula spirula. Scanning Electron Microscope investigations of the shell reveal a complex microstructural organization. The saccharides constitute a quantitatively important moiety of the matrix, as shown by Fourier-transform infrared and solid-state nuclear magnetic resonance spectroscopies. NMR identified ß-chitin and additional polysaccharides for a total amount of 80% of the insoluble fraction. Proteomics was applied to both soluble and insoluble matrices and in silico searches were performed, first on heterologous metazoans models, and secondly on an unpublished transcriptome of Spirula spirula. In the first case, several peptides were identified, some of them matching with tyrosinase, chitinase 2, protease inhibitor, or immunoglobulin. In the second case, 39 hits were obtained, including transferrin, a serine protease inhibitor, matrilin, or different histones. The very few similarities with known molluscan shell matrix proteins suggest that Spirula spirula uses a unique set of shell matrix proteins for constructing its internal shell. The absence of similarity with closely related cephalopods demonstrates that there is no obvious phylogenetic signal in the cephalopod skeletal matrix.

Correction: Diversification rates indicate an early role of adaptive radiations at the origin of modern echinoid fauna.

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

Diversification rates indicate an early role of adaptive radiations at the origin of modern echinoid fauna.

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.

New Eocene Coleoid (Cephalopoda) Diversity from Statolith Remains: Taxonomic Assignation, Fossil Record Analysis, and New Data for Calibrating Molecular Phylogenies.

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.

Deep-time phylogenetic clustering of extinctions in an evolutionarily dynamic clade (Early Jurassic ammonites).

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.

Allometric space and allometric disparity: a developmental perspective in the macroevolutionary analysis of morphological disparity.

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.

Combining ontogenetic and evolutionary scales of morphological disparity: a study of early Jurassic ammonites.

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.