RESUMO
The Permian mesosaurs are well known for being the earliest amniotes to exhibit adaptations for living in a marine environment (Irati-Whitehill Sea). In addition to their set of skeletal features associated with aquatic dwelling life, their dentition includes important characteristics related to feeding in this habitat, which is described in this work, based on the analysis of mesosaur specimens from the Lower Permian Irati Formation of Brazil. Mesosaurs have several slender, conical teeth bordered by enamel apicobasal ridges, a feature predominantly found in aquatic amniotes. Internally, the dentine walls are formed by the arrangement of layers of orthodentine and globular dentine. To prevent tooth loss, the basal area is equipped with plicidentine, a particular type of orthodentine, allied with cementum, alveolar bone trabeculae, and periodontal space that reinforces anchorage and provides some flexibility. The teeth are replaced in a labio-vertical path, and the dentition replaces alternately. This feature is regarded as plesiomorphic, and it ensures the oral cavity is supplied with enough teeth. However, these features do not the assessment of whether mesosaurs teeth were capable of piercing prey with resistant tegument. Instead, we interpret this adaptation as a mechanism for catching prey, at least in adults, and we endorse a possible ontogenetic dietary shift from small to large forms.
RESUMO
This paper describes the use of gamma ray spectrometry in the study of rock samples from the Irati Formation, Paraná sedimentary basin, São Paulo State, Brazil. This technique allowed to measure the natural radiation emitted by 40K, as well the radionuclides belonging to the decay series of 238U (eU = 226Ra = 214Bi) and 232Th (eTh = 228Th = 208Tl) which occur in the analyzed samples. Four gamma ray spectrometers have been utilized for comparing the results obtained: a portable sodium iodide [NaI(Tl)] scintillation detector (Digidart), a handheld bismuth germanate oxide (BGO) detector and two bench NaI(Tl) crystals, differing in their geometry (Planar and Well types). This study involved the calibration of the spectrometers, except in the case of the BGO that is factory calibrated. Afterwards, gamma ray analysis was done for 122 rock samples colleted at Partecal Quarry located at Assistência District, Rio Claro city, which have been of interest for the oil and gas sector. For comparison purposes, the obtained datasets were subjected to different statistical tests, including the analysis of variance (ANOVA) that proved to be of great value for checking the differences of the mean concentration values of eU, eTh and K. The results pointed out several factors that affect the gamma ray analysis for the natural radioelements uranium, thorium, and potassium such as the samples size, shape and geometry, detector type, shielding and counting time. These factors are of difficult control in order to get reliable radiometric measurements by this technique.
Assuntos
Monitoramento de Radiação , Urânio , Brasil , Raios gama , Monitoramento de Radiação/métodos , Espectrometria gama/métodos , Tório/análise , Urânio/análiseRESUMO
ABSTRACT The currently-known extinct Neuropterida fauna of Brazil comprises 18 families, 55 genera and 99 species (Neuroptera: 15 families, 49 genera, 89 species; Raphidioptera: 1 family, 2 genera, 5 species, + 1 genus incertae sedis with 2 species; Megaloptera: 1 family, 2 genera, 2 species; Order incertae sedis: 1 family, 1 genus, 1 species). All of these species have been described since 1980 and they collectively constitute the overwhelming majority of extinct Neuropterida presently known from South America. Other than one species of Permithonidae (Neuropterida incertae sedis) described from the Late Permian Irati Formation (Paraná Basin) of Rio Grande do Sul state, all extinct Brazilian Neuropterida taxa are known only from the Early Cretaceous Crato Formation (Araripe Basin) in Ceará and Pernambuco states. Of the 35 authors who have contributed to the descriptive literature of this fauna over the past 42 years, the work of Brazilian paleontologists Rafael Gioia Martins-Neto [1954-2010] and Maria Aparecida Vulcano-d'Andretta [1921-2018] - who together contributed to the description of 67 species - is especially notable. However, since their deaths, extinct Neuropterida have received little attention from Brazilian scientists and most later work on this fauna has been undertaken by workers outside Brazil. We provide this updated synthesis of the extinct Neuropterida of Brazil in order to centralize baseline knowledge for this fauna, to support efforts to document and conserve Brazilian fossil sites, and to encourage future work on the fauna, particularly by the next generation of Brazilian paleoentomologists.