Esqueletogênese dos ossos da coluna vertebral, costelas e esqueleto abdominal em embriões de Caiman Yacare (Daudin, 1802) (Crocodylia: Alligatoridae) / Skeletogenesis of the vertebral column bones, ribs and inscriptional ribs in embryos of Caiman yacare (Crocodylia: Alligaroridae)

Dentre os répteis, os lagartos e os testudines são o foco de inúmeras investigações que contemplam o estudo de sua ontogenia, contudo, descrições do desenvolvimento e da sequência de ossificação em crocodilianos são escassas. Assim, objetivou-se investigar o padrão de formação e a sequência de ossificação das vértebras e costelas em Caiman yacare (DAUDIN, 1802). Embriões foram coletados em intervalos regulares e submetidos ao protocolo de diafanização e coloração por Aliarina red S. O processo de ossificação da coluna vertebral ocorre no sentido crânio-caudal a partir dos 33 dias. As vértebras se formam a partir de centros de ossificação distintos para os centros, o arco e as apófises. O pró-atlas se forma a partir de dois centros de ossificação distintos que se fundem até o fim do período de incubação. A fusão dorsal dos processos transversos ocorre parcialmente aos 51 dias, dando origem ao diminuto esboço do processo espinhoso. No embrião de 57 dias a articulação entre as costelas, o sacral e o ílio não estava evidente. A morfologia e tamanho das vértebras caudais variam consideravelmente no sentido crânio-caudal. Todas apresentam os processos hemais e iniciam sua ossificação até os 48 dias. C. yacare apresenta um número variado de costelas abdominais, que se ossificam ainda durante o período embrionário. O padrão da esqueletogênese de C. yacare é congruente com de outros répteis, embora existam algumas variações, com particular ênfase na remodelação de estruturas, o que possivelmente reflete as variações do período de incubação entre os diversos répteis relatados.

Among reptiles, lizards and Testudines are the focus of numerous investigations that include the study of its ontogeny, however, descriptions of development and ossification sequence in crocodilians are scarce. Thus, it was aimed to investigate the pattern of training and sequence of ossification of the vertebrae and ribs in Caiman yacare (Daudin, 1802). Embryos were collected at regular intervals and submitted to the protocol of clearing and staining Aliarina red S. The process of ossification of the vertebral column occurs in the craniocaudal direction from the 33 days. The vertebrae are formed from separate ossification centers for the centers, the arch and the transverse processes. The proatlas is formed from two separate ossification centers that fuse to the end of the incubation period. The fusion of dorsal transverse process is partly to 51 days, giving rise to a small sketch of the spinous process. In the embryo of 57 days the link between the ribs, the sacrum and the ilium was not evident. The morphology and size of caudal vertebrae vary considerably in the craniocaudal direction. All have the hemal processes and initiate its ossification up to 48 days. C. yacare has a varied number of abdominal ribs, which ossify even during the embryonic period. The pattern of skeletogenesis C. yacare is consistent with other reptiles, although some variations, with particular emphasis on the remodeling of structures, which possibly reflects the variations in incubation period among the various reptiles reported.

Evolutionary origins of the reptilian brain: the question of putative homologues of dorsal ventricular ridge. An overview and proposal

The reptilian brain is characterized by a structure that bulges into the lateral ventricle, called dorsal ventricular ridge (DVR). The DVR was originally considered to be a part of the basal ganglia, although more recent studies indicate that it may correspond to the dorsal part of the hemisphere. The anterior portion of the DVR has several connectional and functional similarities with parts of the mammalian neocortex, for which reason it has been claimed that the two structures can be considered as homologues. In this article I review the evidence supporting and refuting homology of the DVR with different telencephalic structures of mammals, concluding that it is still early to unequivocally ascribe structural correspondences between the different components in the two vertebrate classes. However, a way out of the problem is suggested by comparing the embryonic position of DVR with that of lateral cortex in the reptilian hemisphere. The lateral cortex is considered to be quite comparable in reptiles and mammals, and hence may be a good marker for the original position of the DVR. If the DVR originates dorsal to lateral cortex, it may be considered comparable to parts of the mammalian neocortex, while if it develops in its same position or ventral to it, it may not correspond to the neocortex. Early embryological work indicated that the DVR develops in the same position as the lateral cortex, but arises as a late migration wave, after cells destined to lateral cortex are generated. In other words, instead of being interposed between dorsal and lateral cortices, the DVR may originate in a position overlapping with lateral cortex. If this alternative turns out to be the case, it may imply that the DVR arose de novo, through an extension of the ancestral period of neuroblast proliferation. As a consequence, there may be no structures comparable to it in other vertebrate classes. Finally, it is also proposed that, regardless of whether the DVR and the extrastriate neocortex can or cannot be considered phylogenetic homologues, some of the integrative functions performed by them might have a common evolutionary origin, that became localized in the reptilian DVR and in the mammalian extrastriate neocortex