O pulmão dos celacantos (Sarcopterygii: Actinistia) e sua homologia com outros grupos de vertebrados: uma abordagem anatômica, ontogenética e paleontológica

Abstract

Lung is a gas exchange organ fundamental for the conquest of land by vertebrates. This organ is primitive in osteichthyans, as it is also present in the basal actinopterygians (polypteriforms) and in the major groups of sarcopterygians. Although anatomically well known, only recently a pulmonary system was formally described for fossil coelacanths (Brito et al., 2010). A vestigial lung apparatus was already mentioned by Millot et al. (1978) on the anatomical description of the first known living species of coelacanths (Latimeria chalumnae). However, the evolutionary history of this system in coelacanths still needs further anatomical, ontogenetic and palaeontological studies. This thesis has as main objective to understand the lung of coelacanths (extants and fossils) by comparing the different ontogenetic stages of this organ and associated structures; as well as to study the evolution of the pulmonary respiratory system and to test its homology in sarcopterygians and actinopterygians. Fossil coelacanths from various palaeontological collections have been examined for comparing the lung of numerous fossil genera and species. Concerning the extant coelacanth Latimeria chalumnae, three-dimensional reconstructions (from CT, MRI, and Synchrotron scans), histological analysis and dissections of the vestigial lung have been performed, and histological slides of air-breathing and buoyancy control organs of other osteichthyan taxa (actinopterygians and sarcopterygians) have been prepared for further comparison purpose. The results corroborate: the primitive state and the homology of the pulmonary complex in osteichthyans; the homology between the lung of fossil and extant coelacanths; the presence of a potentially functional lung in actinistians; the total loss of pulmonary respiration, the reduction of the lungs and the increase of the fatty organ in Latimeria as adaptations to deep waters; the buoyancy control function of the fatty organ of extant coelacanths.