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      Recognition of Truncorotalia Crassaformis As a Modern Planktonic Foraminiferal Morphospecies in the Caribbean and Equatorial Atlantic Ocean and Proposal of a Neotype

      Journal of Foraminiferal Research
      GeoScienceWorld

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          Abstract

          To clarify patterns of within-population variation in Truncorotalia crassaformis and their bearing on selection of a neotype, the shape of shells from two Caribbean sediment traps was analyzed statistically. These data were compared with those from a Holocene equatorial Atlantic core, from topotypes of Globigerina crassaformis Galloway and Wissler (Lomita Quarry, California), and from type specimens of Globorotalia oceanica. This approach was used because the holotype (now destroyed) was the only designated specimen. Morphometric analyses of shells in axial and spiral orientations use data from equally-spaced coordinates around their outlines recorded from SEM imagery. Special attention is given to the profile of the last-formed chamber and to development of a keel at its periphery. Comparison of data from 150 m and 700 m traps shows that the former population includes only small, possibly pre-adult specimens that are non-crusted. Shell shape, especially in axial orientation is much less variable than in the 700 m sample which includes many encrusted and kummerform specimens. Variation in the Holocene sample is closely similar to that in the 700 m trap. Between group comparisons show that the holotype and two paratypes of Globorotalia oceanica plot within the morphospaces of the trap and Holocene samples. All are referred to Truncorotalia crassaformis on the basis of their shape, calcification patterns, and notably the absence of a keel or carina on the final chamber. It is likely that its holotype had this attribute. The axial shape of the neotype is similar to the modelled mean shape of specimens from the sediment traps. Topotypes with a keel on all chambers of the outer whorl are identified as Truncorotalia aff. crassacarina.

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          Planktonic Foraminiferal Species in Pacific Sediments

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            A phylogeny of Cenozoic macroperforate planktonic foraminifera from fossil data.

            We present a complete phylogeny of macroperforate planktonic foraminifer species of the Cenozoic Era (∼65 million years ago to present). The phylogeny is developed from a large body of palaeontological work that details the evolutionary relationships and stratigraphic (time) distributions of species-level taxa identified from morphology ('morphospecies'). Morphospecies are assigned to morphogroups and ecogroups depending on test morphology and inferred habitat, respectively. Because gradual evolution is well documented in this clade, we have identified many instances of morphospecies intergrading over time, allowing us to eliminate 'pseudospeciation' and 'pseudoextinction' from the record and thereby permit the construction of a more natural phylogeny based on inferred biological lineages. Each cladogenetic event is determined as either budding or bifurcating depending on the pattern of morphological change at the time of branching. This lineage phylogeny provides palaeontologically calibrated ages for each divergence that are entirely independent of molecular data. The tree provides a model system for macroevolutionary studies in the fossil record addressing questions of speciation, extinction, and rates and patterns of evolution. © 2011 The Authors. Biological Reviews © 2011 Cambridge Philosophical Society.
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              A Practical Introduction to Landmark-Based Geometric Morphometrics

              Landmark-based geometric morphometrics is a powerful approach to quantifying biological shape, shape variation, and covariation of shape with other biotic or abiotic variables or factors. The resulting graphical representations of shape differences are visually appealing and intuitive. This paper serves as an introduction to common exploratory and confirmatory techniques in landmark-based geometric morphometrics. The issues most frequently faced by (paleo)biologists conducting studies of comparative morphology are covered. Acquisition of landmark and semilandmark data is discussed. There are several methods for superimposing landmark configurations, differing in how and in the degree to which among-configuration differences in location, scale, and size are removed. Partial Procrustes superimposition is the most widely used superimposition method and forms the basis for many subsequent operations in geometric morphometrics. Shape variation among superimposed configurations can be visualized as a scatter plot of landmark coordinates, as vectors of landmark displacement, as a thin-plate spline deformation grid, or through a principal components analysis of landmark coordinates or warp scores. The amount of difference in shape between two configurations can be quantified as the partial Procrustes distance; and shape variation within a sample can be quantified as the average partial Procrustes distance from the sample mean. Statistical testing of difference in mean shape between samples using warp scores as variables can be achieved through a standard Hotelling's T 2 test, MANOVA, or canonical variates analysis (CVA). A nonparametric equivalent to MANOVA or Goodall's F-test can be used in analysis of Procrustes coordinates or Procrustes distance, respectively. CVA can also be used to determine the confidence with which a priori specimen classification is supported by shape data, and to assign unclassified specimens to pre-defined groups (assuming that the specimen actually belongs in one of the pre-defined groups). Examples involving Cambrian olenelloid trilobites are used to illustrate how the various techniques work and their practical application to data. Mathematical details of the techniques are provided as supplemental online material. A guide to conducting the analyses in the free Integrated Morphometrics Package software is provided in the appendix.
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                Author and article information

                Journal
                Journal of Foraminiferal Research
                GeoScienceWorld
                0096-1191
                January 11 2019
                January 11 2019
                : 49
                : 1
                : 94-102
                Article
                10.2113/gsjfr.49.1.94
                5cb7dbcb-03ea-4bd6-bbd2-2027c70a1927
                © 2019
                History

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