Diversity and distribution of the palaeoichthyofauna of the Aptian−Albian Romualdo formation of the Araripe Basin, in Northeastern Brazil

Abstract The objective of this study was to generate new data on the distribution of the Aptian−Albian palaeoichthyofauna of the Araripe Basin, examine its associations with other fossil groups, and reassess its palaeoecological characteristics and taxonomic distribution within the basin and globally. A total of 712 specimens from 27 localities across ten municipalities in the states of Pernambuco, Ceará, and Piauí were analysed, resulting in the identification of 14 families and 21 taxa. Two cluster analyses were performed using the Bray–Curtis index. The first analysis indicated that the assemblage with the greatest diversity and abundance is composed predominantly of marine species ( V. comptoni , R. buccalis , N. brama , C. gardneri , C. cylindricus , Brannerion sp., T. araripis , N. penalvai , S. diasii and P. cearensis ), although their relative abundances vary among different regions of the basin. In contrast, taxa typically associated with lacustrine and lagoonal environments ( Araripelepidotes temnurus , Mawsonia gigas , and Tribodus limae ) are comparatively rare. The second analysis demonstrated a general homogeneity in palaeoichthyofaunal diversity across the basin and enabled comparison of the distributional patterns of marine and euryhaline species among the sampled localities. The fossil assemblages indicate that the sedimentary strata of these ichthyolites were deposited in inner-shelf to proximal marine settings, supporting the predominance of marine taxa. During the Aptian−Albian, the similarity between the palaeoichthyofauna of the Araripe Basin and coeval faunas from the Parnaíba Basin, Colombia, Venezuela, Mexico, Italy, and Tunisia—sharing a total of 11 taxa—suggests that marine incursions into the Araripe Basin likely occurred along a NW−SE direction, through connections with the ancient Tethys Sea.