Taxonomical Review of †Ichthyodectiformes—Actinopterygii, Teleostei—from Cretaceous Period in Brazil 

Ichthyodectiformes are a fossil teleostean lineage originating from the Middle Jurassic to Early Cenozoic period, found in marine and freshwater sediments on every continent. The clade is supported by five synapomorphies and is currently known to exist in over 30 valid species. However, most fossils are poorly preserved or incomplete, and therefore, the synapomorphies for this group are hard to identify or are even homoplastic in many teleostean lineages. This identification problem is recognized, and many authors highlight a combination of characteristic anatomic aspects to identify this group, like the distinctive “bulldog-like” head shape. In Brazil, Ichthyodectiformes are represented by six valid nominal genera (Saurocephalus, Chiromystus, Itaparica, Ogunichthys, Cladocyclus, Cladocynodon) temporally distributed in the Cretaceous period, exclusively on the northeastern sedimentary basins (Araripe, Parnaíba, Recôncavo-Tucano-Jatobá, and Sergipe-Alagoas). Despite these known forms, to this day, there is no comparative anatomical work between the Brazilian species. This work aims to conduct a comparative anatomical and phylogenetic study of Cretaceous species from Brazil to better understand the their interrelationship based on the data available for the taxa in question. The specimens were reviewed by comparative anatomy and analyzed using the program PAUP* 4.0a169 based on the last data matrix to test the intrarelationships of Ichthyodectiformes. Based on the anatomical review, characteristics for the taxa were updated. Compared to the previous results, our analysis resulted in a large polytomy, with no clear affinities for Cladocynodon araripensis, and the relationship between Ichthyodectiformes from Brazil remains unclear. The available material in the collections was insufficient to elucidate the relationships of the Brazilian species. Only the synapomorphies of teeth in a single series and a ventrally enlarged coracoid could be verified in every taxon. A larger sampling effort is recommended to elucidate the phylogeny.