Ascaridoidea (Nematoda) is a widespread superfamily of nematodes that comprises gastrointestinal parasites from all major groups of vertebrates. Although this taxon probably emerged in the Carboniferous, its Brazilian fossil record includes mostly eggs, found in ancient remains, collected in paleontological and archeological sites from the Mesozoic and Cenozoic Eras. The Tremembé Formation (Oligocene of the Taubaté Basin) has become an important source for paleoparasitological studies in avian coprolites during the third decade of the 21st century, with reports of eggs only at only a single cell stage, of embryonic development. Here we present the first egg of Ascaridoidea preserved containing morula, from a bird coprolite recovered from the shales of the Tremembé Formation. Three coprolites, from the outcrop of Aligra Comércio de Argila S/A, Taubaté municipality (State of São Paulo), were rehydrated and subjected to spontaneous sedimentation. Based on morphological and morphometric features and diet and zoopaleontological context, the trace fossils were assigned to piscivorous birds. The egg found showed morphological characteristics typical of Ascaridoidea: namely spherical form, ornamented, and somewhat thick shell. Moreover, this superfamily includes several taxa that infect piscivorous birds and fish in heteroxenous life cycles and produce eggs with similar features as the egg found in the present study. The paleoparasitological information associated with the paleofaunistic diversity of birds and fish from the Tremembé Formation, reveal that the ancient Brazilian paleoenvironments provided subsidies for the rise and success of nematodes infecting these animals during the Paleogene.
Keywords: Oligocene; Taubaté Basin; Tremembé Formation; helminth; nematoda; parasite.