Melanossomos ou bactérias? uma análise de tecido mole encontrado em um fóssil de susisuchus anatoceps (crocodylomorpha, neosuchia)

Abstract

Crocodyliforms presented a series of distinct morphological changes and peculiar behavioral characteristics, occupying different niches. Although its evolutionary history dates back to the Late Triassic, its diversification and radiation date back to the Early Jurassic. Within the group of crocodyliforms, Susisuchus anatoceps is important for phylogenetic positioning, as it presents transitional characteristics between basal and derived groups. The specimen described here was found in the Araripe Basin in the state of Ceará, a place known for the excellent preservation of fossils, especially soft tissues. Thanks to this, it was possible to take images using scanning electron microscopy (SEM), where clusters of ovoid microbodies were identified with the aim of discriminating whether they could be melanosomes or fossilized bacteria. Morphological comparisons were made with other similar studies where these microstructures were found and interpreted as (mostly) melanosomes and others as bacteria. Melanosomes have two types of pigments that derive from melanin: pheomelanins, which are more spherical in shape and have colors between red and yellow, and eumelanins, which have shapes similar to rods and have dark colors between brown and black, shapes very similar to what is seen in the fossil described here, in addition, the sizes of the microbodies may be indicative of eumalanosomes. The location where the fossil was found, comparisons with archosaurs and marine reptiles, and the region of keratinized soft tissue in the fossil suggest that the microbodies are in fact melanosomes and not bacteria. Although morphology helps this interpretation, other lines of evidence are needed, such as the use of chemical analysis techniques, for a more parsimonious conclusion