Pedro S. R. Romano

ARE EXTANT PODOCNEMIDID TURTLES RELICTS OF A WIDESPREAD CRETACEOUS ANCESTOR

Abstract We re-analyzed the most recent morphological data matrix for Pleurodira with inclusion of the Upper Cretaceous Brazilian pleurodiran turtle, Bauruemys elegans (Suárez, 1969), as new Operational Taxonomic Unit. An exhaustive search based on 50 characters for 11 taxa was performed to asses the phylogenetic relationships within the Pelomedusoides and a single most parsimonious tree of 64 steps was found. This new phylogenetic hypothesis places B. elegans as a basal form of Podocnemididae and is used to found a new biogeographic model for the Pelomedusoides. The biogeographical approach was performed with direct analysis of vicariance, using historical sequence of vicariance and phylogenetic information to construct an event-based model. Thus, inspection of distributions maps of Pelomedusoides and the phylogenetic arrangement proposed here were used to correlate cladogenesis and vicariance events during Cretaceous. Current biogeographic hypotheses suggest that living Pelomedusoides distribution and relationships could be the result of large-scale extinctions with extant taxa being relicts of a widespread group. The examination of relationships within Pelomedusoides allows the association of vicariance events of Gondwana fragmentation during the Cretaceous with the isolation of pelomedusoid lineages. We identified three vicariant events: the separation of northern Pelomedusoides and southern Chelidae (node of divergence of Chelidae); the isolation of Africa from Gondwana (node of divergence of Hamadachelys); and the separation of South America and India/Madagascar (node of divergence of Podocnemididnae and Erymnochelyinae). Extant Podocnemidinae (restricted to north South America) would derivate from a south South American source. Its ancestor would have had an autochthons development in South America, expanding its distribution northwards. The presence of Erymnochelyinae in Madagascar would be explained by the migration of a South American ancestor via Antarctica.

Atolchelys lepida, a new side-necked turtle from the Early Cretaceous of Brazil and the age of crown Pleurodira

We report a new pleurodiran turtle from the Barremian Morro do Chaves Formation, Sergipe-Alagoas Basin, Brazil. We tested the phylogenetic position of Atolchelys lepida gen. et sp. nov. by including it in a comprehensive cladistic analysis of pleurodires. The new species is a basal member of Bothremydidae and simultaneously the oldest unambiguous crown Pleurodira. The biogeographic and chronostratigraphic significance of the finding has implications for the calibration of molecular clocks studies by pushing back the minimum age of crown Pleurodira by more than 12 Ma (ca 125 Ma). The reanalysis of Pelomedusoides relationships provides evidence that the early evolution and relationships among the main lineages of side-necked turtles can be explained, at least partially, by a sequence of vicariance events.

New Information about Pelomedusoides (Testudines: Pleurodira) from the Cretaceous of Brazil

Brazilian turtle remains date from the Cretaceous and have been recovered from in 11 different basins. Two of these are of particular importance because of the richness of species and specimens: Araripe (Early Cretaceous) and Bauru (Late Cretaceous). Here we present information based on new material that adds to our understanding of the diversity of turtles from Araripe Basin and provides a basis for discussion of the taxonomic status of some species from Bauru Basin. A new specimen from the Araripe Basin that is from the Crato Formation, although generically indeterminate is proposed to be the oldest representative of the clade Podocnemidera. This allocation would extend the stratigraphic range of the Podocnemidera to the Aptian/Albian, matching that of its sister group, the Pelomedusera. New specimens from the Bauru Basin allow a better understanding of the morphology of the shell in Roxochelys and an assessment and interpretation of diagnostic features used to distinguish Bauru Basin endemic forms. Our preliminary examination of this material leads us to conclude that the diversity described in this basin is overestimated. As consequence, we argue that Bauru Basin includes only two well diagnosed species of turtles: Roxochelys wanderleyi and Bauruemys elegans.

The oldest plesiosaur (Reptilia, Sauropterygia) from Antarctica

Antarctic plesiosaurs are known from the Upper Cretaceous López de Bertodano and Snow Hill Island formations (Campanian to upper Maastrichtian), which crop out within the James Ross Basin region of the Antarctic Peninsula. Here we describe the first plesiosaur fossils from the Lachman Crags Member of the Santa Marta Formation, north-western James Ross Island. This material constitutes the stratigraphically oldest plesiosaur occurrence presently known from Antarctica, extending the occurrence of plesiosaurians in this continent back to Santonian times (86.3–83.5 Mya). Furthermore, MN 7163-V represents the first plesiosaur from this region not referable to the Elasmosauridae nor Aristonectes, indicating a greater diversity of this group of aquatic reptiles in Antarctica than previously suspected.

Intra-specific variation and allometry of the skull of Late Cretaceous side-necked turtle Bauruemys elegans (Pleurodira, Podocnemididae) and how to deal with morphometric data in fossil vertebrates

Background Previous 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. Methods We 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. Results No 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. Discussion ImageJ 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.

Dental eruption sequence and hypsodonty index of a Pleistocene macraucheniid from the Brazilian Intertropical Region

Abstract. Litopterna is represented in the Pleistocene of the Brazilian Intertropical Region by a monospecific genus of Macraucheniidae, Xenorhinotherium. Although most of the knowledge about this family is derived from the dentition, some dental features still remain unknown. This study describes the eruption sequence of permanent dentition and classifies the hypsodonty status of X. bahiense. The specimens studied are from Toca dos Ossos, a limestone cave located in Bahia State. We perform qualitative macroscopic analysis to describe the eruption dental sequence. Additionally, we perform quantitative analysis to determine the hypsodonty index. The dental eruption sequence of the juvenile specimen is M1, M2, I1, I2, M3, I3, P1, P2, P3, and P4. In addition, the analysis of tooth wear in adult specimens provides similar results. The hypsodonty index assigns a mesodont tooth crown for X. bahiense. The dental eruption sequence is most similar to a rapid-growth extant mammal. Moreover, our results do not support afrotherian-like delayed dental eruption to Litopterna. The hypsodonty index can be related to data on vegetation of the Brazilian Intertropical Region and the shape of the premaxilla of X. bahiense, both of which suggest a browsing diet for this macraucheniid.

Comentários sobre o artigo modelagem 3D e suas aplicações na pesquisa paleontológica

Reconstrucoes virtuais tridimensionais sao uma ponderosa ferramenta para pesquisa paleontologica e para entretenimento em educacao. Os metodos e tecnologias disponiveis foram revisados por Dardon et al. (2010), fornecendo uma introducao as tecnicas de obtencao de imagens 3D. Entretanto, algumas informacoes apresentadas no referido trabalho apresentam inconsistencias que sao discutidas aqui. Palavras-chave: paleontologia, modelos 3D, Shape-from-silhouette, scanner 3D, divulgacao cientifica.