Monti and Confalonieri—Comparing the use of phylogenetics and morphometrics in systematics Results
Morphometric analysis.—The first axis of the PCA performed with the log-transformed raw data accounts for 90.58% of the total variability. Because all the variables are negatively correlated with this axis, it explains the variation related to size (Fig. 3.1). Both genera are distributed evenly over the axis, meaning that the two groups do not show differences in size, although Bienvillia has a smaller range of size variation (Fig. 3.1). The PC2 explains 7.08% of the total variability. Both genera appear separated by this axis, Bienvillia is located in the positive values of this axis while Parabolinella, including the type specimens of P.? triarthroides, is in the negative values (Fig. 3.1). Although no variable significantly correlates with PC2, LPA and LPF are those that most contribute to this axis (Table 3). Because LPA and LPF have negative values of the eigenvectors, specimens of Para- bolinella, which lie in the negative region of the PC2, have a more-developed preglabellar field and preglabellar area (Fig. 3.1). Finally the third axis, which explains 0.835% of the total variability, describes variation within each genus. The PCA performed with GMD clearly differentiates both
Figure 2. Parabolinella triarthroides (Harrington, 1938) from the Quebrada Coquena, Purmamarca, Jujuy: (1) dorsal view of the cranidium holotype (CPBA 5); (2) dorsal view of the cranidium paratype (CPBA 54). Scale bars represent 1mm.
Holotype.—Cranidium (CPBA 5, Fig. 2.1) from the late Tremadocian from the Quebrada Coquena, Purmamarca, Jujuy (Harrington, 1938, pl. 7, fig. 10).
Remarks.—Harrington (1938) mentioned a simple preoccipital furrow (S1) in the type specimens of P.
thriarthroides.Later, based on that description, Harrington and Leanza (1957) pro- posed that this species was an intermediate form between the genera Parabolinella and Bienvillia. The generic assignment of P. triarthroides has been questioned by a phylogenetic analysis, which resolved this species as the sister group of Bienvillia Clark, 1924. This analysis recovered a bifurcate preoccipital furrow as the only nonhomoplasic sinapomorphy of the Parabolinella genus (excluded P.? triarthroides) (Monti and Confalonieri, 2013). The holotype of P. triarthroides is poorly preserved and the nature (simple or bifurcate) of the preoccipital furrow (S1) cannot be determinate on this specimen (Fig. 2.1). Nevertheless, the paratype has a bifurcate preoccipital,which is suggested on its left side (Fig. 2.2). Moreover other specimens assigned to this species also have a conspicuous bifurcate preoccipital furrow (Waisfeld and Vaccari, 2003). Additionally, P. tirarthroides has a developed preglabellar area (sag.) and preglabellar field (sag.), a wide posterior fixigenae (tr.), a large glabella and cranidium, and a higher ratio between the width of the interocular genae and the width of glabella (at the eye line) (tr.). All these characters justify the inclusion this species in Parabolinella.
genera, and the type specimens of P.? triarthroides are located within the range of variation of Parabolinella (Fig. 3.2). The PC1 positively correlates with WPF, LPA, and LPF, and negatively correlates with the LOR, LC, Lgl, WOR, and Wgl.B (Table 4). The positive values of the first axis include specimens with a smaller glabella and occipital ring, wider posterior fixigenae (tr.), and a more developed pregla- bellar area and preglabellar field (sag.). The negative values of the first axis include specimens with a more-developed axis of the cephalon (bigger glabella and occipital ring), narrower posterior fixigenae (tr.), and shorter preglabellar area and preglabellar field (sag.). Both genera can be distinguished by the first axis, while they are evenly distributed over the second one (Fig. 3.2). Species of Parabolinella are located on the positive values of the first axis. This genus is characterized by a wider posterior fixigenae and more-developed preglabellar area and preglabellar field (Fig. 4.1). On the contrary, species of Bienvillia are located completely on the negative values of the first axis. This genus has a bigger axis of the cephalon (larger and wider glabella and occipital ring), narrower posterior fixigenae (tr.), and shorter preglabellar area (sag.) and preglabellar field (sag.) (Fig. 4.2). The specimens of P.? triarthroides are included within the range of variation of Parabolinella (Fig. 3.2). Therefore, P.? triarthroides and Parabolinella share a similar cranidium morphology. When RD was used, similar results to GMD analysis were
obtained. The specimens of Bienvillia are located on the negative values of the PC1, while those of the Parabolinella genus are mostly found on the positives values. Even if an over- lapping zone can be recognized, the types of P.? triarthroides are located on the most-positive values of the PC1 (Fig. 3.3). Some differences on the variables that contribute to the PC1 axis are observed, compared to the GMD analysis. In addition, confidence intervals for the loadings of these variables were bigger than those obtained with GMD (Tables 4, 5). The PC1
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