Notário em pterossauros e aves : aspectos evolutivos, ontogenéticos e morfo-funcionais

Abstract

Notarium in pterosaurs and birds: evolutionary, ontogenetic and morphofunctional aspects The notarium, also known as "Os Dorsale" is the structure formed from a group of fused vertebrae in the dorsal region that occurs independently in two groups of flying vertebrates: pterosaurs and birds. Its evolutionary development depends on mutations that alter the expression patterns of HOX and PAX genes and is a structure generally acquired in the stage of skeletal maturation (juvenile to adult). The fusion may involve two to six or seven different truncated vertebrae (dorsal in pterosaurs or thoracic in birds) and in much cases also the last cervical. The fusion can occur to different degrees, joining only the vertebral bodies, the neural spines, the transverse processes, the ventral processes, only some or even all this sites. In this study, our goal is the identify and characterize the evolutive, ontogenetic and morpho-functional patterns of the notarium. The published bibliography was consulted on the theme, available in Scopus, Elsevier, Springer and Scielo. and analyzed around of 200 skeletons of current and fossil birds deposited in the collections of ornithology from the Pontifícia Universidade Católica do Rio Grande do Sul (PUCRS), Fundação Zoobotânica do Rio Grande do Sul (FZB-RS), Museu de História Natural de Taubaté (MNHT-SP) and Museu Paraense Emílio Goeldi (MPEG-PA) and about 80 specimens of pterosaurs from paleontological collections of the Natural History Museum, London, UK (NHM), Staatliches Museum für Naturkunde, Stuttgart, De (SMNS), Bayerische Staatssammlung für Paläontologie und Geologie, München, De (BSP) and American Museum of Natural History, New York, USA (AMNH), to identify diagnostic structures, patterns of fusion, ossification, tendons. We measured the long bones of the anterior and posterior limbs of all the complete specimens, computed in a matrix and statistically analyzed in the Excel and PAST programs, using Principal Component Analysis (PCA) to identify distinct groups in the morphology of the notarium, combining with ecological, morphological, geological and biomechanical data. We divided the results into four chapters: In the first one, we identified the oldest record of the notarium in Pterosauria from the Upper Jurassic of Germany and analyzed the occurrence of this structure throughout the clade along the geological time, focusing its morphological and phylogenetic patterns; in the second, we describe the differences between the notarium of several groups of birds, updating the presence of the character in the fossil record and the new molecular phylogenetic analyzes of Neornithes, and discussing its origin, evolution and relation with the habit of life; and in the third chapter, we identify different stages in the sequence of fusion of the vertebrae that compose the notarium, starting from the first or second “true” dorsal, extending to the last notarial (usually fourth thoracic in birds and sixth dorsal in the pterosaurs), independently in the neural spines, strongly influenced by the ossified tendons at the apex. We can conclude that the notarium evolved in two distinct moments, separated by almost 100 million years between pterosaurs in the Jurassic and birds in the Paleocene; during the transition from ranforrinchoids to pterodactyloids, possibly due to changes in the center of mass; and in the Neornithes at the time of forest advance, possibly linked to abrupt takeoff conditions. In many specimens we can identify the different ontogenetic stages, which hold similarities and differences between the two groups. It is a complex structure, but through detailed morphological and morphometric analyzes, and of deeper studies involving combined biomechanics, embryology and genetics, it is possible to identify their real meaning.