BackgroundPrevious quantitative studies on Bauruemys elegans (Suárez, 1969) shell variation, as well as the taphonomic interpretation of its type locality, have suggested that all specimens collected in this locality may have belonged to the same population. We rely on this hypothesis in a morphometric study of the skull. Also, we tentatively assessed the eating preference habits differentiation that might be explained as due to ontogenetic changes.MethodsWe carried out an ANOVA testing 29 linear measurements from 21 skulls of B. elegans taken by using a caliper and through images, using the ImageJ software. First, a Principal Components Analysis (PCA) was performed with 27 measurements (excluding total length and width characters; =raw data) in order to visualize the scatter plots based on the form variance only. Then, a second PCA was carried out using ratios of length and width of each original measurement to assess shape variation among individuals. Finally, original measurements were log-transformed to describe allometries over ontogeny.ResultsNo statistical differences were found between caliper and ImageJ measurements. The first three PCs of the PCA with raw data comprised 70.2% of the variance. PC1 was related to size variation and all others related to shape variation. Two specimens plotted outside the 95% ellipse in PC1∼PC2 axes. The first three PCs of the PCA with ratios comprised 64% of the variance. When considering PC1∼PC2, all specimens plotted inside the 95% ellipse. In allometric analysis, five measurements were positively allometric, 19 were negatively allometric and three represented enantiometric allometry. Many bones of the posterior and the lateral emarginations lengthen due to increasing size, while jugal and the quadratojugal decrease in width.DiscussionImageJ is useful in replacing caliper since there was no statistical differences. Yet iterative imputation is more appropriate to deal with missing data in PCA. Some specimens show small differences in form and shape. Form differences were interpreted as occuring due to ontogeny, whereas shape differences are related to feeding changes during growth. Moreover, all outlier specimens are crushed and/or distorted, thus the form/shape differences may be partially due to taphonomy. The allometric lengthening of the parietal, quadrate, squamosal, maxilla, associated with the narrowing of jugal and quadratojugal may be related to changes in feeding habit between different stages of development. This change in shape might represent a progressive skull stretching and enlargement of posterior and lateral emargination during ontogeny, and consequently, the increment of the feeding-apparatus musculature. Smaller individuals may have fed on softer diet, whereas larger ones probably have had a harder diet, as seen in some living species of Podocnemis. We conclude that the skull variation might be related to differences in feeding habits over ontogeny in B. elegans.
Background. Crown-Pleurodira (i.e.: Cheloides and Pelomedusoides) possess a side-necked retraction mode with specialized cervical vertebrae (CV) anatomy. Moreover, there are distinctive ecological features among its lineages, as the convergent long neck in species of Chelidae and in the extinct pelomedusoid Araripemydidae. Also, the CV5-CV6 articulation is the major point of flexure in neck retraction and reflects a key point for the evolution of Pleurodira. Here we evaluated CV5 shape variation within some Pleurodira groups with emphasis on some Brazilian fossil species. Methods. We analyzed the fifth CV of eight species and 14 specimens comprising four pleurodiran clades (Chelidae, Araripemydidae, Bothremydidae and Podocnemididae) in order to assess the shape variation via geometric morphometry. All specimens were photographed in caudal view under the same protocol, and eight landmarks (LM) were picked at the left side of each vertebrae using TPSDig2. Data were Procrustes superimposed and a Relative Warps Analysis (RWA) was performed using TPSRelw v1.49. Results. RW1 and RW2 summarized 68.63% of the shape variance. The scatter of the specimens revealed distinctiveness between Podocnemidoidea (Podocnemididae+Bothremydidae) and Araripemys+Chelidae paraphyletic group. Such variation is due to (1) a medial contraction of the surface of the postzygapophysis, (2) a taller neural spine and (3) a more rounded vertebral condile towards Podocnemidoidea. Podocnemididae showed greater variation: a Podocnemis sextuberculata specimen (MZSP3218) is more alike to Cearachelys placidoi (Procrustes Distances, PD=0.17) than other podocnemidids and Bauruemys elegans resembles P. unifilis (PD=0.11). Also, other P. sextuberculata specimen (MZSP3217) is more alike to the Araripemys-Chelidae group. Discussion. Previous works have noticed the anatomical similarities between both longnecked chelids and A. barretoi, considering it as a convergence since they are from different clades. Our data showed the same pattern and, assuming the current phylogenetic relationships of Pleurodira, this might indicates similar feeding behavior between living Hydromedusa and Chelus and Araripemys. The Podocnemidoidea morphospace variation is consistent with the phylogeny, since C. placidoi is nested among Podocnemis spp., and this might indicate a more specialized CV5 for the former and a possible convergence with some Podocnemis species. Also, the resemblance of P. unifilis CV5 with B. elegans seems to indicate a morphotype similar to the podocnemidid ancestor for this living species. Despite our scanty sample, it shows a notable variation in Podocnemis spp. and at least two convergences among CV5 within Pleurodira. Further studies with additional sampling might shed light on a more complex evolution of CV specializations in side-necked turtles than previously assumed.
Background. Crown-Pleurodira (i.e.: Cheloides and Pelomedusoides) possess a side-necked retraction mode with specialized cervical vertebrae (CV) anatomy. Moreover, there are distinctive ecological features among its lineages, as the convergent long neck in species of Chelidae and in the extinct pelomedusoid Araripemydidae. Also, the CV5-CV6 articulation is the major point of flexure in neck retraction and reflects a key point for the evolution of Pleurodira. Here we evaluated CV5 shape variation within some Pleurodira groups with emphasis on some Brazilian fossil species. Methods. We analyzed the fifth CV of eight species and 14 specimens comprising four pleurodiran clades (Chelidae, Araripemydidae, Bothremydidae and Podocnemididae) in order to assess the shape variation via geometric morphometry. All specimens were photographed in caudal view under the same protocol, and eight landmarks (LM) were picked at the left side of each vertebrae using TPSDig2. Data were Procrustes superimposed and a Relative Warps Analysis (RWA) was performed using TPSRelw v1.49. Results. RW1 and RW2 summarized 68.63% of the shape variance. The scatter of the specimens revealed distinctiveness between Podocnemidoidea (Podocnemididae+Bothremydidae) and Araripemys+Chelidae paraphyletic group. Such variation is due to (1) a medial contraction of the surface of the postzygapophysis, (2) a taller neural spine and (3) a more rounded vertebral condile towards Podocnemidoidea. Podocnemididae showed greater variation: a Podocnemis sextuberculata specimen (MZSP3218) is more alike to Cearachelys placidoi (Procrustes Distances, PD=0.17) than other podocnemidids and Bauruemys elegans resembles P. unifilis (PD=0.11). Also, other P. sextuberculata specimen (MZSP3217) is more alike to the Araripemys-Chelidae group. Discussion. Previous works have noticed the anatomical similarities between both longnecked chelids and A. barretoi, considering it as a convergence since they are from different clades. Our data showed the same pattern and, assuming the current phylogenetic relationships of Pleurodira, this might indicates similar feeding behavior between living Hydromedusa and Chelus and Araripemys. The Podocnemidoidea morphospace variation is consistent with the phylogeny, since C. placidoi is nested among Podocnemis spp., and this might indicate a more specialized CV5 for the former and a possible convergence with some Podocnemis species. Also, the resemblance of P. unifilis CV5 with B. elegans seems to indicate a morphotype similar to the podocnemidid ancestor for this living species. Despite our scanty sample, it shows a notable variation in Podocnemis spp. and at least two convergences among CV5 within Pleurodira. Further studies with additional sampling might shed light on a more complex evolution of CV specializations in side-necked turtles than previously assumed.
Background. Previous quantitative studies about Bauruemys elegans (Suárez, 1969) shell variation, as well as the taphonomy interpretation of its type locality, have suggested that all specimens collected in this locality may have belonged to the same population. We rely on this hypothesis in a morphometric study of the skull. Also, we tried to assess the eating preference habits differentiation that might be explained as due to ontogenetic changes.Methods. We took 29 linear measurements from 21 skulls of B. elegans. First, a Principal Components Analysis (PCA) was performed using 27 measurements (excluding total length and width characters) in order to plot the overall individual dispersion in PCs to visualize patterns of scattering based on the form variance. Secondly, PCA was carried out using ratios of length and width of each original measurement to assess shape variation among individuals. Finally, original measurements were log-transformed to describe allometries along the ontogenetic development.Results. The first three PCs of the first analysis comprising 70.2% of the variance. PC1 was related to size variation and all others related to shape variation. MCZ4123 and MN7071-V have been plotted outside the 95% ellipse in PC1xPC2 axes. The first three PCs of the second analysis comprising 64% of the variance. When considering PC1xPC2 and PC2xPC3, all specimens have been plotted inside the 95% ellipse, which is in contrast to PC1xPC3 in which two individuals (MCT1753- R and MN6750-V) are outliers. In the third analysis, five measurements were positively allometric, 18 were negatively allometric and four represent truly negatively allometry. All bones of the posterior and the lateral emarginations, as well as the squamosal, lengthen due to size increasing, different from the jugal and the quadratojugal which decrease in width.Discussion. Some specimens show small differences in form (MCZ4123 and MN7071-V) and shape (MCT1753-R and MN6750-V). Form differences were already detected in a shell morphometry study, but interpreted as due to ontogeny, which might be the case of the present data. Moreover, all outlier specimens are crushed and/or distorted, thus the form/shape differences might be partially due to taphonomy. The allometric lengthen of parietal, quadrate, squamosal, maxilla, associated with the narrowing of jugal and quadratojugal may be related to changes in feeding habit between different stages of development. This change in shape might represent a progressive skull stretching and enlargement of posterior and lateral emargination during ontogeny, and consequently, the increment of the feeding-apparatus musculature. Smaller individuals may have fed of softer diet whereas bigger ones probably have had a harder diet, as seen in some living species of Podocnemis. We conclude that the skull variation is higher than expected and might be related to differences in feeding habits along the ontogeny of B. elegans.
Background. Previous quantitative studies about Bauruemys elegans (Suárez, 1969) shell variation, as well as the taphonomy interpretation of its type locality, have suggested that all specimens collected in this locality may have belonged to the same population. We rely on this hypothesis in a morphometric study of the skull. Also, we tried to assess the eating preference habits differentiation that might be explained as due to ontogenetic changes.Methods. We took 29 linear measurements from 21 skulls of B. elegans. First, a Principal Components Analysis (PCA) was performed using 27 measurements (excluding total length and width characters) in order to plot the overall individual dispersion in PCs to visualize patterns of scattering based on the form variance. Secondly, PCA was carried out using ratios of length and width of each original measurement to assess shape variation among individuals. Finally, original measurements were log-transformed to describe allometries along the ontogenetic development.Results. The first three PCs of the first analysis comprising 70.2% of the variance. PC1 was related to size variation and all others related to shape variation. MCZ4123 and MN7071-V have been plotted outside the 95% ellipse in PC1xPC2 axes. The first three PCs of the second analysis comprising 64% of the variance. When considering PC1xPC2 and PC2xPC3, all specimens have been plotted inside the 95% ellipse, which is in contrast to PC1xPC3 in which two individuals (MCT1753- R and MN6750-V) are outliers. In the third analysis, five measurements were positively allometric, 18 were negatively allometric and four represent truly negatively allometry. All bones of the posterior and the lateral emarginations, as well as the squamosal, lengthen due to size increasing, different from the jugal and the quadratojugal which decrease in width.Discussion. Some specimens show small differences in form (MCZ4123 and MN7071-V) and shape (MCT1753-R and MN6750-V). Form differences were already detected in a shell morphometry study, but interpreted as due to ontogeny, which might be the case of the present data. Moreover, all outlier specimens are crushed and/or distorted, thus the form/shape differences might be partially due to taphonomy. The allometric lengthen of parietal, quadrate, squamosal, maxilla, associated with the narrowing of jugal and quadratojugal may be related to changes in feeding habit between different stages of development. This change in shape might represent a progressive skull stretching and enlargement of posterior and lateral emargination during ontogeny, and consequently, the increment of the feeding-apparatus musculature. Smaller individuals may have fed of softer diet whereas bigger ones probably have had a harder diet, as seen in some living species of Podocnemis. We conclude that the skull variation is higher than expected and might be related to differences in feeding habits along the ontogeny of B. elegans.
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