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Journal of Paleontology 91(4):685–714
second principal component (30.2% of the total variance), focusing on the maximum width of the laterals negatively cor- related with the maximum width of both basal and infralaterals. The thecal geometry of Rhopalocystis varies continuously
from a conical shape associated with a tenuous or large aboral region (lower left and lower right quadrants, respectively) to an inflated claviform geometry associated with a narrow basis and an elongate aboral region (upper left quadrant) via a moderate obconical morphology associated with a long adoral region (upper right quadrant). The cladistically defined morphotypes R. fraga, R. grandis,and R. havliceki are located in the periphery of the scatter plot (Fig. 6.2). The morphotype R. fraga is distinguished by a conical theca with both basal and infralaterals as wide as the laterals, and a narrow and elongate adoral region. The large morphological variability shown by the two other morphotypes (R. grandis, R. havliceki)ismoredifficult to interpret because of the reduced number of individuals. The last two morphotypes, R. destombesi and R. zagoraensis, are largely overlapping in the center of the PCA plot, thus suggesting a similar but variable thecal geometry (Fig. 6.2). A MANOVA associated to a linear discriminant analysis
(LDA) was performed to test the validity of the morphotypes identified by the cladistic analysis and further recognized pro parte by the PCA. The species R. grandis could not be included in these analyses because measurements could be made only on two complete specimens (1725a, b; the third available specimen of R. grandis, 1725c, corresponds to a fragment of the aboral part of a theca; see Systematic Paleontology). The MANOVA evidences a highly significant multivariate differ- ence between the four remaining species: Wilk’s λ =0.087, d.f. = 24, 179.1, Rao’sF = 7.56, p = 5.4 ×10−17. The post hoc contrast analysis (pairwise comparisons, using Hotelling’s T² tests coupled with a sequential Bonferroni’s correction for multiple testing) shows highly significant differences for four of the six species couples, a marginally to nonsignificant difference between R. fraga and R. havliceki, and a nonsignificant difference between R. destombesi and R. zagoraensis, indicating that these two species cannot be distinguished geometrically on the basis of these six linear descriptors (Table 2). The LDA correctly assigns 75% of the specimens to their predefined morphotypes, with all misclassifications occurring between R. destombesi and R. zagoraensis, as expected from the contrast analysis (Fig. 6.3).
Discussion.—The cladistic and morphometric analyses together
indicate that the genus Rhopalocystis may be constituted of five distinct morphological species. Both analyses show that the three morphological species R. fraga, R. grandis, and R. havliceki can be readily distinguished on their dimensional geometry and on the organization and ornamentation of
Table 2. Results of the contrast analysis (pairwise comparisons, using Hotell- ing’sT² tests coupled with a sequential Bonferroni’s correction for multiple testing) associated with the MANOVA.
R. fraga
R. destombesi R. zagoraensis R. havliceki
0.00055292 0.00013658 0.066057
R. destombesi 0.30292 0.00013673 1.75E-06 R. zagoraensis
the theca. R. fraga has a small, strawberry-shaped theca, com- posed of five circlets of plates and a wider than high basal plate. R. grandis is a large-sized species. Its radial plates are almost hemispherical, and most of its thecal plates are ornamented with small punctiform granulations. R. havliceki also has a large- sized theca; its radials and some of its laterals are spine-shaped, and its infralaterals are ornamented with one to three elongated protuberances. The morphometric analysis shows that the two morpho-
logical species R. destombesi and R. zagoraensis share comparable thecal geometries, mostly based on similar thecal length-width proportions. However, the specimens belonging to R. destombesi could reach a greater size: the theca of the longest specimen measures 50mm, while the longest specimen observed for R. zagoraensis reaches only 21mm. Moreover, the cladistic analysis illustrates that these two species can be easily distinguished by the organization of the theca, its ornamentation, the number of radial circlets, and the shape of radial plates. In R. zagoraensis, the theca is usually composed of six primary plate circlets (including three radials circlets) instead of seven primary plate circlets (comprising four radial circlets) in R.
destombesi.In R. zagoraensis, radials are globular (almost hemispheric, while they can also be convex), but they are more frequently conical with a blunt summit in R. destombesi. The thecal plates of R. destombesi are usually smooth, whereas those of R. zagoraensis are covered with vermiculated radiating ridges. Moreover, the examined specimens of R. destombesi never showed more than one circlet of secondary plates between the infralaterals and the laterals. By contrast, the theca of R. zagoraensis exhibits a high number of additional secondary plates, with up to three intercalary circlets between infralaterals and laterals. Finally, the basal plate in R. zagoraensis can be split to two elements. R. destombesi, R. zagoraensis,and R. havliceki show a
relatively large polymorphism. The variability of R. destombesi mainly results from the complexity of the thecal plating, ranging from none to two additional complete intercalary circlets (one between infralaterals and laterals, and another between laterals and radials). The thecal plates are usually smooth, but they sometimes showa nipple-shaped central umbo. In R. zagoraensis, the polymorphism is more pronounced. The thecal plating varies strongly because of the varying size and number of secondary plates, either isolated or organized in complete circlets: one to three circlets intercalated between infralaterals and laterals and another complete one between laterals and
radials.Moreover, the particular ornamentation of R. zagoraensis varies strongly: it can range frombeing restricted to small vermicular ridges on the basal plate to very extensive and consisting of continuous and elongated folds all over the theca. The morphological variability in R. havliceki concerns the
ornamentation. Its infralaterals and laterals bear one, two, or three rounded to spine-shaped umbos. Some differences in the ornamentation can be observed between the populations coming from the localities Z-F1 and Z-F12c. The Z-F1 specimens exhibit only one spine-shaped protuberance, whereas those from Z-F12c show one, two, or three rounded protuber- ances on their laterals. This variation might reflect either environmental differences between their habitats or evolution- ary adaptations.
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