Sergio Furtado Cabreira

New stem-sauropodomorph (Dinosauria, Saurischia) from the Triassic of Brazil

Post-Triassic theropod, sauropodomorph, and ornithischian dinosaurs are readily recognized based on the set of traits that typically characterize each of these groups. On the contrary, most of the early members of those lineages lack such specializations, but share a range of generalized traits also seen in more basal dinosauromorphs. Here, we report on a new Late Triassic dinosaur from the Santa Maria Formation of Rio Grande do Sul, southern Brazil. The specimen comprises the disarticulated partial skeleton of a single individual, including most of the skull bones. Based on four phylogenetic analyses, the new dinosaur fits consistently on the sauropodomorph stem, but lacks several typical features of sauropodomorphs, showing dinosaur plesiomorphies together with some neotheropod traits. This is not an exception among basal dinosaurs, the early radiation of which is characterized by a mosaic pattern of character acquisition, resulting in the uncertain phylogenetic placement of various early members of the group.

Tooth histology of the parareptile Soturnia caliodon from the Upper Triassic of Rio Grande do Sul, Brazil

A histological analysis of the dentition of the small procolo− phonid parareptile Soturnia caliodon reveals detailed infor− mation concerning tooth implantation and replacement for this taxon. The presence of acrodont tooth implantation is ver− ified, which contradicts current models for procolophonid dentition. A heterogeneous enamel layer, that reaches large thickness on the cusps, and a broad secondary dentine are also recorded. These structures provide a very stable occlusal mor− phology that extends the useful life of the teeth. During the process of replacement, old teeth were not pushed out but re− absorbed. The evidence indicates that Soturnia caliodon had a very low rate of tooth replacement which constitutes a valu− able adaptation for its high−fibre herbivorous niche.

Tooth Microstructure of the Early Permian Aquatic Predator Stereosternum tumidum

A histological investigation of the feeding apparatus of a Stereosternum specimen revealed a great number of adaptations in the structure and insertion of teeth, to deal with breakage risks. The tooth wall is composed of different layers of dentine, varying in orientation and composition. This mixed arrangement may have increased tooth resistance to lateral tension. The tooth insertion also involves more than one mechanism. The teeth are located inside shallow tooth sockets and are held in place by a tripartite periodontium (composed of alveolar bone, cementum and possibly soft periodontal tissue) and accessory structures, here termed anchorage trabeculae (mainly composed of cementum). Fully grown teeth are ankylosed to the bottom of the tooth socket. The recognition of alveolar bone and cementum (and the possible presence of a soft periodontal ligament) reinforces the idea that these tissues were widespread among Amniota, not being exclusive to mammals and archosaurs. The adaptations identified here reinforce the hypothesis that Stereosternum was an active aquatic predator.

Occurrence of giant stereospondyl remains in the Santa Maria Formation (Middle/Upper Triassic of southern Brazil)

The first occurrence of stereospondyl remains in the Santa Maria Formation (Middle/Upper Triassic) of the Paraná Basin is reported. The material is fragmentary but indicates the presence of large stereospondyls in the Carnian of this unit. The lack of informative characters is an obstacle, but the specimens probably belong to metoposaurids, trematosaurids or mastodonsauroids. Most South American reports of stereospondyls record fragmentary remains (except for the Argentinean chigutisaurids, and the Brazilian Australerpeton cosgriffi—a rhinesuchoid, and Sangaia lavinai—a rhytidosteid), and this situation constrains generalized attempts to understand their likely sequence of occupation in this part of Gondwana during the upper Palaeozoic and lower Mesozoic. Nevertheless, this new record is important, since it increases the representation of stereospondyls in southern Brazil. Moreover, it expands their biostratigraphic range in the Rosário do Sul Group.

The femoral anatomy of Pampadromaeus barberenai based on a new specimen from the Upper Triassic of Brazil

Femora of the holotype and only previously known specimen of the early sauropodomorph Pampadromaeus barberenai are incomplete and fractured. Here, we describe a new complete femur assigned to Pampadromaeus barberenai, quarried from the same outcrop of original type specimen: ‘Janner’ site, (Carnian of the Paraná Basin). It shares with the holotype of Pampadromaeus barberenai a unique combination of features: anteromedial tuber slightly posteromedially displaced; lesser trochanter proximodistally oriented with the proximal tip gently connected to the femoral shaft; fourth trochanter located on the medial margin along the mediolateral axis of the femur and with an assymetrical outline. In addition, we propose a femoral autapomorphy for Pampadromaeus barberenai: lateral condyle of the distal end of the femur extremely reduced lateromedially. Two distinct phylogenetic analyses place the new specimen as the sister-group of the Pampadromaeus barberenai type-specimen and, in one of them, they are nested within Sauropodomorpha, corroborating the original description and taxonomic assignation.