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959 results for “GeoMetre”
Taxonomic identification using virtual palaeontology and geometric morphometrics: a case study of Jurassic nerineoidean gastropods
<p><span>Taxonomic identification of fossils is fundamental to a wide range of geological and biological disciplines. Many fossil groups are identified based on expert judgment, which requires extensive experience and is not always available for the specific taxonomic group at hand. Nerineoideans, a group of extinct gastropods that formed a major component of Mesozoic shallow marine environments, have distinctive internal spiral folds that form the basis for their classification at the genus level. However, their identification is often inconsistent because it is based on a set of selected characters reliant upon individual interpretation. </span></p> <p><span>This study shows a non-destructive and quantitative method for their identification using micro-CT and geometric morphometrics. We examined and micro-CT-scanned nerineoidean specimens from five main families that dominated Europe, Arabia and Africa during the Middle-Late Jurassic. Optimal longitudinal slices were selected from the tomographic reconstructions or from images of polished cross-sections compiled from fossil collections, published work and online databases. Internal whorl outlines were represented by thirty evenly distributed sliding semilandmarks and shape variations were studied using the Procrustes-based geometric morphometrics method. Multivariate analysis shows that Ceritellidae and Ptygmatididae are distinct families, whereas Nerinellidae, Eunerineidae and Nerineidae fall within the same shape variance and cannot be distinguished based on internal whorl outlines. The suggested method can be applied to images from various sources as well as to poorly preserved specimens. Our case study demonstrates the importance of quantitatively re-evaluating taxonomy in the fossil record, promoting the future utility of large datasets. </span></p>
FIGURE 1 in Use of scalation landmarks in geometric morphometrics of squamate reptiles: a comment on homology
FIGURE 1. Diagrams of specimens of the Crotalus viridis complex with 14 (A) and 16 (B) supralabial scales, respectively (supralabial scale rows are shaded in grey). For (A), the red dot marks a fixed landmark at the center of the series, seven scales from the first and seven scales from the last supralabial scale. Placing a corresponding fixed landmark on specimen B requires that one choose between seven scales from the first supralabial, seven scales from the last supralabial, or the suture at the center of the series, providing three mutually exclusive options (red dots). Selecting any of these options changes the topological position of the landmark relative to the first, the last, or both of these scales in the series. Fixed landmarks applied to scale rows variable in count renders secondary homology intractable, regardless of whether scales are counted from a consistent anchor point.
Data from: Geometric morphometric analysis applied to theropod tracks from the lower Cretaceous (Berriasian) of Spain
Geometric morphometric methods applied to theropod tracks from the Huérteles Formation (Berriasian, Spain) are here shown to be invaluable for drawing comparisons between theropod tracks with different preservation modes (true tracks, shallow undertracks and natural casts) or differing in the preservation of anatomical features (e.g. digital pads). Principal components analysis and thin-plate spline methods can quantitatively distinguish between the broad groups of tracks in a sample and establish the main differences between them. These methods offer a promising approach for estimating ichnodiversity, achieved by evaluating just the morphology of the tracks independent of other factors such as size. The theropod tracks of the Huérteles Formation can be classified into two broad groups: minute-to-medium-sized gracile theropod tracks (Kalohipus bretunensis) and medium-to-large-sized robust theropod tracks (Iberosauripus). The presence of a third group of more gracile medium-to-large-sized theropod tracks (Megalosauripus) cannot be proven with certainty on the basis of the current data. These results indicate that the theropod ichnodiversity of the Huérteles Formation is probably lower than that estimated by means of conventional methods alone (e.g. qualitative description of the tracks) and that many of the described theropod morphotypes may represent extramorphological or ontogenetic variations of other morphotypes.
Data from: Geometric morphometric analyses of worn cheek teeth help identify extant and extinct gophers (Rodentia: Geomyidae)
Studies of the biostratigraphy and palaeoecology of fossil vertebrate assemblages require large samples of accurately identified specimens. Such analyses can be hampered by the inability to assign isolated and worn remains to specific taxa. Entoptychine gophers are a diverse group of burrowing rodents found in Oligo-Miocene deposits of the western United States. In both entoptychines and their extant relatives the geomyines, diagnostic characters of the occlusal surface of the teeth are modified with wear, making difficult the identification of many isolated fossil teeth. We use geometric morphometrics to test the hypothesis that tooth shape informs taxonomic affinities and expected levels of morphological variation across gopher taxa. We also incorporate data from microcomputer tomography to investigate changes in occlusal surface shape through wear within individuals. Our analyses demonstrate the usefulness of our approach in identifying extant geomyines to the genus, subgenus and species levels, and fossil entoptychines to the genus and, in some cases, the species level. Our results cast doubt on the validity of some species within Entoptychus and suggest future revisions to entoptychine taxonomy. The amounts of morphological divergence observed among fossil and extant genera are similar. Fossil species do not differ greatly from extant ones in that regard either. Further work evaluating the morphological variation within and across entoptychine species, including unworn teeth and osteological material, will allow revised analyses of the biostratigraphy and palaeoecology of important Oligo-Miocene mammalian assemblages of the western United States and help to infer the phylogenetic relationships and evolution of gophers.
Data from: Taxonomic revision of genus Ablattaria Reitter (Coleoptera, Silphidae) employing geometric morphometrics
The genus Ablattaria Reitter, 1884 (Coleoptera: Silphidae: Silphinae) is revised. Four taxa are recognized as valid species: Ablattaria arenaria (Kraatz, 1876), A. cribrata (Ménétries, 1832), A. laevigata (Fabricius, 1775) and A. subtriangula Reitter, 1905. Ablattaria laevigata var. meridionalis Ganglbauer, 1899 is newly treated as a junior subjective synonym of A. laevigata. Lectotypes are designated for Phosphuga arenaria Kraatz, 1876, Ablattaria arenaria var. punctigera Reitter, 1884, Ablattaria arenaria var. alleoni Portevin, 1926, Silpha cribrata Ménétries, 1832, Silpha laevigata Fabricius, 1775, Silpha gibba Brullé, 1832, Ablattaria gibba var. costulata Portevin, 1926, Ablattaria gibba var. distinguenda Portevin, 1926, Ablattaria gibba var. punctata Portevin, 1926 and Ablattaria subtriangula Reitter, 1905. The distribution of all taxa is mapped, based on material examined. Geometric morphometric methods were used to evaluate shape variability in Ablattaria. Results indicated sexual dimorphism in all species. Shape inconsistency was found between the sexes of all taxa when tested independently. The first two relative warp axes indicated 65.17% shape variation in males and 65.72% in females. Canonical variate analysis separated the taxa studied. There was minimal overlap between some groups in both sexes. Differences in body shape between populations of A. laevigata from Central Europe, Italy and Greece + Turkey were also examined. Relative warps implied 58.01% shape variability on both axes in males and 64.78% in females. CVA revealed noticeable overlaps between the groups, although the Italian population demonstrated a higher separation in both sexes.
Data from: Untangling phylogenetical, geometrical and ornamental imprints on Early Triassic ammonoid biogeography: a similarity-distance decay study.
Ammonoids are diverse and widespread fossil shelly cephalopods that flourished in the world ocean during more than 300 million years before their total extinction, 65 million years ago. In spite of two centuries of intensive scientific studies, their mode(s) of life, and most particularly long-distance dispersal abilities remain poorly known. Here we address this question by looking at the latitudinal distribution of Early Triassic (~250 Myr) ammonoids through similarity-distance decay analyses. We examine and compare how rates of similarity-distance decay differ between various systematic, shell geometry and ornamentation groups, during the same ~3.5 myr Early Triassic time interval, in order to untangle phylogenetical, geometrical and ornamental imprints on the observed biogeographical pattern. Our data do not support any phylogenetical and shell ornamentation control on the similarity-distance decay, but rather evidence a significant effect of (sub-)adult shell geometry: most evolute morphs tend to have been more endemic than most involute ones. This result contrasts with the classical hypothesis that long-distance ammonoid dispersal mainly occurred during the earliest planktonic young stages, and thus that (sub-)adult morphological characteristics should not constrain large-scale biogeographical patterns of ammonoids. While a direct control by Sea Surface Temperature can be discarded, this result may indicate that at least some adult Triassic ammonoid morphs were good active swimmers able to achieve long-distance migrations, as observed for some present-day coleoid cephalopods.
Data from: Taxonomic and evolutionary pattern revisions resulting from geometric morphometric analysis of Pennsylvanian Neognathodus conodonts, Illinois Basin
Conodont fossils are highly valuable for Paleozoic biostratigraphy and for interpreting evolutionary change, but identifying and describing conodont morphologies, and characterizing gradual shape variation remain challenging. We used geometric morphometrics (GM) to conduct the first landmark-based morphometric analysis of the biostratigraphically useful conodont genus Neognathodus. Our objective is to assess whether previously defined morphotype groups are reliably distinct from one another. As such, we reevaluate patterns of morphologic change in Neognathodus P1elements, perform maximum likelihood tests of evolutionary modes, and construct novel, GM-based biozonations through a Desmoinesian (Middle Pennsylvanian) section in the Illinois Basin. Our GM results record the entire spectrum of shape variability among Neognathodus morphotypes thus alleviating the problem of documenting and classifying gradual morphologic transitions between morphotypes. Statistically distinct GM groups support previously established classifications of N. bassleri, N. bothrops, and N. roundyi. Statistically indistinct pairs of GM groups do not support literature designations of N. medadultimus and N. medexultimus, and N. dilatus and N. metanodosus, and we synonymize each pair. Maximum likelihood tests of evolutionary modes provide the first statistical assessment of Neognathodus evolutionary models in the Desmoinesian. The most likely evolutionary models are an unbiased random walk or a general random walk. We name four distinct biozones through the Desmoinesian using GM results and these align with previous biozonation structure based on the Neognathodus Index (NI) illustrating that Neognathodus-based biostratigraphic correlations would not change between GM or NI methods. The structural similarity between both biozonations showcases that determining GM-based biozones is not redundant, as this comparison validates using landmark-based GM work to construct viable biozonations for subsequent stratigraphic correlations. Although this study is limited to the Illinois Basin, our quantitative methodology can be broadly applied to additional genera to test taxonomic designations, interpret statistically-robust evolutionary patterns, and construct valid biozones for this significant chordate group.
Data from: Dealing with allometry in linear and geometric morphometrics: a taxonomic case study in the Leporinus cylindriformis group (Characiformes: Anostomidae) with description of a new species from Suriname
To achieve maximum efficacy, taxonomic studies that seek to distinguish amongst species must first account for allometric shape variation within species. Two recently developed software packages (SMATR and MorphoJ) offer regression-based allometric approaches that are notable for their statistical power and ease of use and that may prove highly useful to taxonomists working with linear or geometric morphometric data. We investigate species delimitation of the slender-bodied fishes in the Leporinus cylindriformis group using these programs and demonstrate the utility of the allometric corrections that they provide. Without allometric correction, many pairs of species are difficult to distinguish on the basis of morphometrics, but once regressions are used to account for marked allometric variation within species, most of the recognized species in this group can be readily distinguished with linear or geometric morphometrics, particularly using variation in the depth of the body. Both approaches returned congruent patterns of separation amongst putative species, but the geometric approach in MorphoJ distinguished amongst four more pairs of species than did the linear approach in SMATR and appears to provide slightly more statistical power. Based on distinctive morphometrics, meristics, and coloration, a highly elongate species of Leporinus from the Suriname, Corantijn, and Coppename rivers of Suriname is described herein as a new species, Leporinus apollo sp. nov. The unique L. cylindriformis holotype from Porto de Moz, Brazil differs in morphology, meristics, and pigmentation from specimens commonly referred to that species from the main basin of the Amazon; the latter specimens may represent an additional undescribed species. The L. cylindriformis holotype itself may represent a rare species or a specimen collected at the edge of its native range. Measurements of the holotype and paratype of Leporinus niceforoi, which were collected in the Amazonian slope of Colombia, differ substantially from similarly pigmented and putatively conspecific specimens from Amazonian portions of Ecuador and Peru. Recently collected specimens from Colombia are needed to determine whether the observed morphometric variation encompassed by the current concept of L. niceforoi indicates a morphocline within a single species, suggests the presence of multiple cryptic species, or results from shrinkage of the types. In all these cases, linear or geometric morphometric data can reliably differentiate amongst species, but only after one accounts for allometric shape variation. The new SMATR and MorphoJ software packages both offer easy and effective approaches to such allometrically informed taxonomy, and may prove useful to any systematist working on taxa that change shape as they grow.
Geometric model
Source: Objaverse 1.0 / Sketchfab
Geometric model
*(метка 1)* Source: Objaverse 1.0 / Sketchfab
Geometric model
* *(метка Р75)* Source: Objaverse 1.0 / Sketchfab
Geometric model
*(метка 24)* Source: Objaverse 1.0 / Sketchfab
FIGURE 5 in Sexual dimorphism in a freshwater atyid shrimp (Decapoda: Caridea) with direct development: a geometric morphometrics approach
FIGURE 5. Relative deformations grids show the variation in the mean shape of the second abdominal segment for (a) females and (b) males.
FIGURE 4 in Sexual dimorphism in a freshwater atyid shrimp (Decapoda: Caridea) with direct development: a geometric morphometrics approach
FIGURE 4. Scatter plot of first versus second principal component axes for the total variation of the second abdominal pleura shape for females and males in Neocaridina davidi.
FIGURE 1 in Sexual dimorphism in a freshwater atyid shrimp (Decapoda: Caridea) with direct development: a geometric morphometrics approach
FIGURE 1. Location of landmarks and semilandmarks on each anatomic structure in Neocaridina davidi. (a) carapace; (b) second abdominal pleura; left side, lateral view.
FIGURE 3 in Geometric morphometrics uncovers a new species of ponyfish (Teleostei: Leiognathidae: Equulites), with comments on the taxonomic status of Equula berbis Valenciennes
FIGURE 3. Landmarks (1) rostral tip of premaxilla, (2) posterior end of nuchal spine, (3) anterior insertion of dorsal fin, (4) posterior insertion of dorsal fin, (5) dorsal insertion of caudal fin, (6) midpoint of caudal border of hypural plate, (7) ventral insertion of caudal fin, (8) posterior insertion of anal fin, (9) anterior insertion of anal fin, (10) dorsal base of pelvic fin, (11) ventral end of lower jaw articulation, (12) posterior end of maxilla, (13) anterior margin through midline of eye, (14) posterior margin through midline of eye, (15) dorsal end of opercle, (16) dorsal base of pectoral fin. Base figure is modified from Nelson (2006).
FIGURE 5 in Geometric morphometrics uncovers a new species of ponyfish (Teleostei: Leiognathidae: Equulites), with comments on the taxonomic status of Equula berbis Valenciennes
FIGURE 5. Holotype of Equulites absconditus (AMNH 249306; 74.0 mm SL, adult male) showing the distinct sexspecific translucent flank patch that concentrates light on the body during photic display.
FIGURE 4 in Geometric morphometrics uncovers a new species of ponyfish (Teleostei: Leiognathidae: Equulites), with comments on the taxonomic status of Equula berbis Valenciennes
FIGURE 4. Canonical variates analysis showing two distinct shape groups along CV 1 individuals and the holotype.
FIGURE 2 in Geometric morphometrics uncovers a new species of ponyfish (Teleostei: Leiognathidae: Equulites), with comments on the taxonomic status of Equula berbis Valenciennes
FIGURE 2. Specimens of Group A morphotype (A—Western Indian Ocean) and Group B morphotype (B—Eastern Indian Ocean)
FIGURE 3 in Sexual dimorphism in a freshwater atyid shrimp (Decapoda: Caridea) with direct development: a geometric morphometrics approach
FIGURE 3. Relative deformations grids illustrating the variation in the mean shape of the carapace for (a) females and (b) males.
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Allen Brain Atlas
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