Morphometric study of fossil and extant spores of the family anemiaceae from the lower cretaceous to the quaternary

Abstract

This study is based on the morphometry of 112 morphospecies of fossil spores of the Family Anemiaceae (Class Polypodiopsida, Order Schizaeales), collected from several strata of Brazilian basins, ranging from the Lower Cretaceous up to the Quaternary, as well as on the morphometry of spores of 129 living species of this family around the world. The objective of the study is to analyze the relationship among their morphometric characters, chronostratigraphy and climate/paleoclimate. The following parameters were established: D1 (larger diameter), D2 (smaller diameter), EM (width of the muri) and DM (distance between the muri). Measurements in micrometers were saved in an Excel spreadsheet in order to make regression analysis charts, which showed the following results: (1) perfect linear correlation between D1 and D2, regardless of geological age and climate, which was expected, as spores of Anemiaceae are equidimensional; (2) no perfect linear correlation between D1 and EM, and an increase in D1, caused by an increase in the denseness of their muri. The lack of linearity is noticeable in Lower Cretaceous species, in which thin muri predominate. In the Lower Cretaceous, the densest murus is no thicker than 4 µm, whereas, in the Upper Cretaceous, muri of up to 8 µm were observed. Regardless of the kind of climate, reasonable linearity was observed among extant species, which are devoid of very thin muri; (3) there is no correlation between EM and DM in species from the Cretaceous to the Tertiary, showing a wide range of DM values for each EM value. This result was expected, as the muri denseness and the distance between the muri are, a priori, independent parameters. In the Cretaceous, DM values are generally low, and values lower than 2 µm predominate. In the Tertiary, DM values vary from 0.5 µm to 6 µm. An inverse relationship between EM and DM is shown for living species, especially species of the semi-arid to semi-humid regions. Fossil species did not show this relationship due to the existence of species with thin and dense muri (e.g., Cicatricosisporites microstriatus, C. minutaestriatus and C. avnimelechi) and species with walls of median thickness and great distance between them (e.g., Cicatricosisporites hughesii and C. purbeckensis).